Literature

We at VALIMET are proud and excited to collaborate with Universities and Research Institutes from various countries.
See below a list of selected publications reporting studies made with our powders.

Search All Topics

Article Topics

Atomization Technology

Works co-authored by VALIMET Technology Manager Ian McCarthy

(PDF) High Frame Rate Analysis Of The Spray Cone Geometry During Close-Coupled Gas Atomization (researchgate.net)

A.M.Mullis, N.J.E. Adkins, Z. Aslam, I.N. McCarthy and R.F. Cochrane

Abstract

The geometry of the spray cone during the atomization of Ni31.5Al68.5 alloy within a close-coupled gas atomizer operating with a generic die and nozzle design has been studied using high speed digital video techniques. A Kodak Ektapro 4540mx high speed motion analyser fitted with high magnification optics has been used to record details of a region extending 5 cm from the spray nozzle at frame rates of up to 18,000 frames per second. The material was sprayed at a temperature of a1830 K (corresponding to a superheat of around 200 K), wherein sufficient thermal radiation was emitted for filming to take place without any additional lighting source. In order to quantitatively analyse the large number of still frames that result (up to 65536), image processing routines capable of automating this process have been developed. These have been used to measure the optical brightness and the position of the optical intensity maximum of the material passing though a narrow window at a fixed distance from the nozzle tip. The results of this analysis show that spray cone consists of a jet that precesses around the centre axis of the atomizer in a very regular manner at a frequency around 360 Hz. In order to understand the origins of this motion further experiments have been conducted with a laboratory scale analogue atomizer which atomizes a water jet. We have found that the frequency of precession is essentially independent of the atomizing gas pressure used but does depend upon the geometry of both the die and nozzle used during atomization.

Close-coupled gas atomization: High-frame-rate analysis of spray-cone geometry | Request PDF (researchgate.net)

A.M. Mullis, N.J.E. Adkins, Z. Aslam, I.N. McCarthy and R.F. Cochrane

Abstract

The geometry of the spray cone during atomization of Ni 31.5Al68.5 in a close-coupled gas atomizer operating with a generic die and nozzle design has been studied utilizing high-speed digital video techniques. Details of the region extending 5 cm from the spray nozzle at frame rates of up to 18,000 frames/s were recorded. The material was sprayed at a temperature ∼ 1,830 K (corresponding to a superheat ∼200 K), wherein sufficient thermal radiation was emitted for images to be recorded without any additional lighting, In order to quantitatively analyze the large number of still frames that result (up to 65,536), image processing routines capable of automating this process have been developed and used to measure the optical brightness and the position of the optical-intensity maximum of the material passing though a narrow window at a fixed distance from the nozzle tip. The results of this analysis show that the spray cone consists of a jet that precesses around the center axis of the atomizer in a regular manner at a frequency ∼360 Hz. In order to understand the origin of this motion, further experiments were conducted with a laboratory-scale analogue atomizer which atomizes a water jet It was found that the frequency of precession is essentially independent of the atomizing-gas pressure, but does depend upon the geometry of both the die and nozzle.

(PDF) High speed imaging and Fourier analysis of the melt plume during close coupled gas atomisation (researchgate.net)

I.N. McCarthy, N.J.E. Adkins, Z. Aslam, A.M. Mullis, R.F. Cochrane

Abstract

A high speed digital analysis technique has been used to study the atomisation plume of a superheated sample of Ni–Al in a close coupled gas atomiser. The atomisation, incorporating a generic melt nozzle and die design was captured using a Kodak high speed digital analyser at a frame rate of 18 k frames per second. The resulting 65 536 frames were then analysed using a specially designed routine, which calculates values of optical brightness and position of the intensity maximum for all frames and performs Fourier analysis on the sequence. The data produced from this analysis show that the plume, pulses at low frequencies (<25 Hz) and precesses at higher frequencies (∼360 Hz) around the atomiser’s centreline. To aid investigation into the origins of this precession and other phenomena it was decided to conduct further experiments using an analogue system. The analogue atomiser reproduces the important features of the full atomiser but instead of atomising molten metal, the analogue system atomises water, providing a quick and easy way of testing the effects of changing parameters. Using this system it was found that the precession of the melt plume is independent of the atomiser’s gas inlet pressure but strongly dependent on both the die and melt nozzle’s geometry

Investigation of the pulsation phenomenon in close-coupled gas atomization | Request PDF (researchgate.net)

A.M. Mullis, I.N. McCarthy, R.F. Cochrane, N.J.E. Adkins

Abstract

High speed photography coupled with sophisticated image analysis has been used to study the low frequency pulsation in the volume of melt being instantaneously delivered to the melt nozzle during close-coupled gas atomization. We find that at low gas pressures the distribution of material at the melt tip can be described by a log-normal distribution. At high gas pressure the distribution is better described by two superimposed log-normal distributions, one with a high standard deviation when there is little melt at the atomizer tip and a second with a lower standard deviation when there is more melt at the atomizer tip. We associate this behavior with the transition between open- and closed-wake conditions in the gas. We suggest that the methodology proposed represents a simple, non-invasive technique for characterising the performance of gas atomizers.

(PDF) Log-Normal Melt Pulsation in Close-Coupled Gas Atomization (researchgate.net)

A.M. Mullis, R.F. Cochrane, I.N. McCarthy, N.J.E. Adkins

Abstract

High speed photography coupled with sophisticated image analysis has been used to study low-frequency pulsation during close-coupled gas atomization. At high gas pressure the instantaneous melt delivery is described by two superimposed log-normal distributions, one with a high standard deviation but little melt at the atomizer tip, the second with low standard deviation but more melt at the atomizer tip. At low gas pressures the distribution is better described by a single log-normal distribution.

Numerical and experimental modelling of back stream flow during close-coupled gas atomization | Request PDF (researchgate.net)

S. Motaman, A.M. Mullis, R.F. Cochrane, I.N. McCarthy, D.Borman

Abstract

This paper reports the numerical and experimental investigation into the effects of different gas jet mis-match angles (for an external melt nozzle wall) on the back-stream flow in close coupled gas atomization. The Pulse Laser Imaging (PLI) technique was applied for visualising the back-stream melt flow phenomena with an analogue water atomizer and the associated PLI images compared with numerical results. In the investigation a Convergent–Divergent (C–D) discrete gas jet die at five different atomization gas pressures of 1–5 MPa, with different gas exit jet distances of 1.65, 1.6, 1.55, 1.5, 1.45 and 1.40 mm from the melt nozzle external wall, was combined with four melt nozzles of varying gas jet mis-match angles of 0°, 3°, 5°, and 7° relative to the melt nozzle external wall (referred to as nozzle types 1–4). The results show that nozzle type 1 with the smallest mis-match angle of zero degrees has highest back-stream flow at an atomization gas pressure of 1 MPa and a gas die exit jet located between 1.65 mm and 1.5 mm from the external melt nozzle wall. This phenomenon decreased with increasing mis-match angle and at higher atomization gas pressure. For nozzle type 2, with a mis-match angle of 3 degrees, a weak back-stream flow occurred with a gas exit jet distance of 1.65 mm from the melt nozzle external wall. For a gas pressure of 1 MPa with a decrease in the gas jet exit distance from the external wall of the melt nozzle this phenomenon was eliminated. This phenomenon was not seen for nozzle types 3 and 4 at any gas pressure and C–D gas exit jet distances.

Energetic Materials Technology

Purdue University

May 2022

DOI: https://www.researchgate.net/publication/360862668_On_the_Use_of_Fluorine-Containing_Nano-Aluminum_Composite_Particles_to_Tailor_Composite_Solid_Rocket_Propellants

Kyle Uhlenhake, Omar R. Yehia, Andrew Noel, Brandon C. Terry

Abstract

The burning rate of solid propellants is an important factor for optimizing rocket motors and improving performance. The enhanced burning rate can increase thrust and reduce a propulsion system‘s overall size and weight. In this study, a novel nano‐aluminum/THV composite additive was prepared and introduced into a solid ammonium perchlorate/polybutadiene composite solid rocket propellant to enhance its burning rate. The morphology of the composite particle additive and its effects on combustion were characterized. The use of small quantities (<15 wt.%) of the additive resulted in a burning rate enhancement of up to 2.1 times that of the conventional coarse aluminized propellant with a specific impulse loss of only 3 seconds, and as much as 4.7 times enhancement with a predicted loss of 22 seconds in theoretical specific impulse. Some of this loss may be recovered by the improved combustion efficiency in smaller rocket motors because the additive was shown to significantly reduce the aluminum agglomeration at the propellant burning surface and reduce the size of reaction products which may reduce two‐phase flow losses. The additive also provides wide burning rate tailorability, favorable for motor, grain, and thrust curve design. The burning rate enhancement mechanism is thought to be a physical cratering mechanism governed by the burning rate disparity between the binder/oxidizer system and the nano‐aluminum/fluoropolymer additive and not a chemical catalytic effect.

December 2016

DOI: https://docs.lib.purdue.edu/open_access_dissertations/975/

Hatem Mohamed Belal

Abstract

Agglomeration reduction techniques are important field in solid propellant industry, Large agglomeration results in excessive two phase losses. Tailored composite particles has been applied to tailor aluminum particle ignition and combustion. In this research, mechanical activated aluminum magnesium powders are synthesized, tested in both laser ignition using CO2 and propellant. Prepared powders categorized into particle size that suitable for propellant application. Laser ignition tests showed that the prepared powder are more reactive than magnalium which has the same Al:Mg weight ratio. Agglomeration capturing showed that the prepared powder produce much less than neat aluminum or even similar physical mixture of aluminum and magnesium. The burning rate of propellant using the prepared powder is increased.

MA Al/Mg powders as long as with comparable physical mixture are applied in propellant formulation with AP/HTPB. In order to quantify the effect of changing Mg percent. Burning rate is measured from videos captured for strand burning in windowed pressure vessel, also the agglomeration was capturing using special setup. The results showed that MA powder increase burning rate and this increase reach maximum at 50% Mg, while propellant using physical mixture of Al/Mg show constant or little decrease in burning rate. In addition, the MA powder show lower agglomeration size in comparison to neat aluminum propellant or physical mixture with the same Mg percent. The lowest agglomeration sizes were for MA50. However, equilibrium calculation showed 4 sec losses in specific impulse, so MA 70 was chosen as a compromise between low agglomeration size at the minimum loss in specific impulse.

Magnalium is an alloy of aluminum and magnesium and it is known for its ease of ignition and high oxidation energy content. It has been used as a metal fuel to increase burning rates of composite modified double base (CMDB) and ammonium perchlorate (AP) composite propellants. However, the ignition temperature is larger than the comparable mechanically activated (MA) Al-Mg powder.
Mechanical milling was performed on magnalium powders and modifications of structure and morphology of the alloy during milling were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The prepared magnalium powder was used in a solid propellant, which showed higher burning rates than those containing as-received magnalium. Furthermore, milled magnalium showed higher agglomeration reduction than both as received magnalium as well as MA Al-Mg powders.

Extend the application of mechanical alloying of aluminum to other metals with extreme difference in melting/ boiling temperature, the first is Zirconium which is a long time candidate in solid propellant community. The ease of zirconium ignition and the micro-explosive behavior shown by neat zirconium particles promote its usage in agglomeration reduction effort. the other metal is Indium, which has very low melting point compared to other metal, this may open the possibility of earlier reaction of aluminum particles at or near propellant surface resulting in less pre ignition time which reduce agglomeration tendency.

MA of 90% Aluminum and 10% of Zirconium or 10% Indium using High energy ball milling, particle characterization using SEM/FIB, XRD and DSC/TGA are performed, burning rate and agglomeration size analyses of solid propellant using sieved MA-powder are done. The results showed that the both MA Al-ZR and MA Al-In ignite in laser beam which verify change in reactivity from neat aluminum with its protective alumina coating. However, burning rate results show no change in burning rate from neat aluminum, also the prepared material shows no reduction in agglomeration sizes.

DOI: doi.org/10.1002/prep.202200204

Kyle E. Uhlenhake, Diane N. Collard, Alexander C. Hoganson, Alex D. Brown, Sara Fox, Metin Örnek, Jeffrey F. Rhoads and Steven F. Son

Abstract

Aluminum (Al) and polyvinylidene fluoride (PVDF) composites can be used in many unique applications in the field of energetic materials. Due to their low melting point, many PVDF composites can be additively manufactured. However, more research is needed to better understand the ignition and combustion of these materials. Manipulating the size of aluminum (Al) particles in Al/PVDF composites can drastically alter the burning rate, ignition characteristics, and possibly flame temperatures. This study characterizes the ignition of additively manufactured microand nano- Al/PVDF composites through hotwire ignition tests. Both nAl and μAl particles were mixed in PVDF at 20 wt.% and additively manufactured into disks via fused filament fabrication. The nAl/PVDF printed disks ignited at a minimum ignition power (MIP) of 4.1 W compared to the 9.5 W required for ignition of μAl/PVDF disks. At identical powers, ignition delays were significantly shorter for nAl/PVDF disks. Additionally, while the nAl/PVDF disks reacted instantaneously at any power above their MIP, the μAl/PVDF disks exhibited smaller, localized flames before complete combustion, if the power was below 17.5 W. Flame temperatures were estimated through three-color pyrometry and compared to thermochemical equilibrium calculations. While theoretical flame temperatures for nAl/PVDF and μAl/PVDF are 2023 K and 2314 K respectively, both samples burned near 2000 K when measured using pyrometry.

October 2022

DOI: https://www.sciencedirect.com/science/article/abs/pii/S001021802200267X?via%3Dihub

Diane N. Collard, Kyle E. Uhlenhake, Metin Örnek, Jeffrey F. Rhoads and Steven F. Son

Abstract

Solid propellants are employed in a range of applications from the inflation of airbags to propulsion systems for rockets. The ignition of solid propellants must be carefully controlled and modified on a per-use basis due the specific ignition requirements of each application. Using tailored photoreactive materials as a source of ignition for solid propellants, or other energetic materials, could reduce the added weight and risk of traditional initiators and result in safer, more effective solid rocket motor ignition systems. This study demonstrates the tunability of the ignition delay and propagation properties of optically-sensitive, nearly full density reactive aluminum/polyvinylidene fluoride (Al/PVDF) films and additively manufactured igniters. A single printed layer of pure nano-aluminum (nAl) at ideal stoichiometry in PVDF was found to flash ignite, but frequently yielded delayed transitions in steady propagation from the igniter to the propellant. To improve the continuity and steadiness of the transition, fuel particle size, igniter thickness, and a combination of layers of nAl and micron-sized aluminum (μAl) were investigated. In printed igniters with layers of μAl, only a single layer of nAl was needed to flash ignite the material and propagate to the layers of μAl without delay. For igniters cast onto strands of ammonium perchlorate composite propellant, continuous ignition was achieved with a single layer of nAl printed atop a triple layer of μAl for the flash-activated igniters and a single layer of nAl printed atop a single and triple layer of μAl for laser-driven igniters. The nAl/PVDF layer enabled good flash or laser ignition sensitivity, while the μAl/PVDF produced more sustained heat transfer to produce a reliable ignition process.

October 2020

DOI: https://arc.aiaa.org/doi/10.2514/1.B37848

Gabriel A. Diez, Timothy D. Manship, Brandon C. Terry, Ibrahim E. Gunduz and Steven F. Son

Abstract

Aluminum (Al)/lithium (Li)-alloy-based fuels can potentially improve composite propellant performance and reduce hydrochloric acid formation. Shattering microexplosions have been observed in Al–Li-based composite propellants at 0.1 MPa; however, combustion characterization of Al–Li-based propellant as a function of pressure has not been performed previously. Measurement of the burning rate of an Al–Li composite propellant and quantification of agglomerate production near the propellant surface at various pressures are presented in this work. Al–Li particle agglomeration, determined to be unconsumed Al–Li, increased with increasing pressure, suggesting that microexplosions were inhibited at higher pressures. Burning rate experiments demonstrated a plateau burning rate effect that occurred in propellant with fine grade (mean diameter: 17  μm) Al–Li particles, whereas the as-received Al–Li-containing (mean diameter: 53  μm) propellant maintained a constant pressure exponent of about 0.39 over all pressures tested. The finer Al–Li propellant had a pressure exponent of 0.59 at pressures below about 4 MPa and a pressure exponent of 0.11 above 4 MPa. Surface imaging of the Al–Li propellant showed a distinctive condensed phase reaction on the surface, which became more prominent with the finer Al–Li particles and at higher pressures: a potential source of the plateau burning rate effect.

2021

DOI: https://www.sciencedirect.com/science/article/abs/pii/S1540748920302492?via%3Dihub

Morgan D. Ruesch, Austin J. McDonald, Garrett C. Mathews, Steven F. Son, Christopher S. Goldenstein

Abstract

Understanding the temperature of aluminized, composite-propellant flames is critical to achieving robust rocket motor designs and developing accurate, predictive models for propellant combustion. This work presents measurements of (1) the temperature of CO (within the flame bath gas) and (2) the temperature of AlO (located primarily within regions surrounding the burning aluminum particles) within aluminized, composite-propellant flames as a function of height above the burning propellant surface. Three aluminized, ammonium-perchlorate (AP), hydroxyl-terminated polybutadiene (HTPB) composite propellants with varying aluminum particle size (nominally 31 �m, 4.5 �m, or 80 nm) and one non-aluminized AP-HTPB propellant were studied while burning in air at 1 atm. A wavelength-modulation-spectroscopy technique was utilized to measure CO temperature and mole fraction via mid-infrared wavelengths and a conventional AlO emission-spectroscopy technique was utilized to measure the temperature of AlO. The bath-gas temperature varied significantly between propellants, particularly within 2 cm of the burning surface. The propellant with the smallest particles (nano-scale aluminum) had the highest average temperatures and far less variation with measurement location. At all measurement locations, the average bath-gas temperature increased as the initial particle size of aluminum in the propellant decreased, likely due to increased aluminum combustion. The results support arguments that larger aluminum particles can act as a heat sink near the propellant surface and require more time and space to ignite and burn completely. On a time-averaged basis, the temperatures measured from AlO and CO agreed within uncertainty at near 2650 K in the nano-aluminum propellant flame, however, AlO temperatures often exceeded CO temperatures by  ≈ 250 to 800 K in the micron-aluminum propellant flames. This result suggests that in the flames studied here, and on a time-averaged basis, the micron-aluminum particles burn in the diffusion-controlled combustion regime, whereas the nano-aluminum particles burn within or very close to the kinetically controlled combustion regime.

April 2018

DOI: https://doi.org/10.2514/1.B36859

Michael S. Powell, Ibrahim W. Gunduz, Weixiao Shang, Jun Chen, Steven F. Son, Yi Chen and Daniel R. Guildenbecher

Abstract

Aluminized ammonium perchlorate composite propellants can form large molten agglomerated particles that may result in poor combustion performance, slag accumulation, and increased two-phase flow losses. Quantifying agglomerate size distributions are needed to gain an understanding of agglomeration dynamics and ultimately design new propellants for improved performance. Due to complexities of the reacting multiphase environment, agglomerate size diagnostics are difficult and measurement accuracies are poorly understood. To address this, the current work compares three agglomerate sizing techniques applied to two propellant formulations. Particle collection on a quench plate and backlit videography are two relatively common techniques, whereas digital inline holography is an emerging alternative for three-dimensional measurements. Atmospheric pressure combustion results show that all three techniques are able to capture the qualitative trends; however, significant differences exist in the quantitative size distributions and mean diameters. For digital inline holography, methods are proposed that combine temporally resolved high-speed recording with lower-speed but higher spatial resolution measurements to correct for size–velocity correlation biases while extending the measurable size dynamic range. The results from this work provide new guidance for improved agglomerate size measurements along with statistically resolved datasets for validation of agglomerate models.

February 2017

DOI: https://www.sciencedirect.com/science/article/abs/pii/S0010218016303078?via%3Dihub

Mario A. Rubio, I. Emre Gunduz, Lori J. Groven, Travis R. Sippel, Chang Wan Han, Raymond R. Unocic, Volkan Ortalan, Steven F. Son

Abstract

Aluminum particles are widely used as a metal fuel in solid propellants. However, poor combustion efficiencies and two-phase flow losses result due in part to particle agglomeration. Recently, engineered composite particles of aluminum (Al) with inclusions of polytetrafluoroethylene (PTFE) or low-density polyethylene (LDPE) have been shown to improve ignition and yield smaller agglomerates in solid propellants. Reductions in agglomeration were attributed to internal pressurization and fragmentation (microexplosions) of the composite particles at the propellant surface. Here, we explore the mechanisms responsible for microexplosions in order to better understand the combustion characteristics of composite fuel particles. Single composite particles of Al/PTFE and Al/LDPE with diameters between 100 and 1200 µm are ignited on a substrate to mimic a burning propellant surface in a controlled environment using a CO2 laser in the irradiance range of 78–7700 W/cm2. The effects of particle size, milling time, and inclusion content on the resulting ignition delay, product particle size distributions, and microexplosion tendencies are reported. For example particles with higher PTFE content (30 wt%) had laser flux ignition thresholds as low as 77 W/cm2, exhibiting more burning particle dispersion due to microexplosions compared to the other materials considered. Composite Al/LDPE particles exhibit relatively high ignition thresholds compared to Al/PTFE particles, and microexplosions were observed only with laser fluxes above 5500 W/cm2 due to low LDPE reactivity with Al resulting in negligible particle self-heating. However, results show that microexplosions can occur for Al containing both low and high reactivity inclusions (LDPE and PTFE, respectively) and that polymer inclusions can be used to tailor the ignition threshold. This class of modified metal particles shows significant promise for application in many different energetic materials that use metal fuels.

January 2012

DOI: https://www.researchgate.net/publication/269621306_Combustion_of_bimodal_aluminum_particles_and_ice_mixtures

Terrence L. Connell, Jr., Grant A. Risha, Richard A. Yetter, Vigor Yang, & Steven F. Son

Abstract

The combustion of aluminum with ice is studied using various mixtures of nano- and micrometersized aluminum particles as a means to generate high-temperature hydrogen at fast rates for propulsion and power applications. Bimodal distributions are of interest in order to vary mixture packing densities and nascent alumina concentrations in the initial reactant mixture. In addition, the burning rate can be tailored by introducing various particle sizes. The effects of the bimodal distributions and equivalence ratio on ignition, combustion rates, and combustion efficiency are investigated in strand experiments at constant pressure and in small lab-scale [1.91 cm (0.75 in.) diameter] static firedrocket-motor combustion chambers with center-perforated propellant grains. The aluminum particles consisted of nanometer-sized particles with a nominal diameter of 80 nm and micron-sized particles with nominal diameters of 2 and 5 μm. The micron particle addition ranged from 0% to 80% by active mass in the mixture. Burning rates from 1.1 (160 psia) to 14.2 MPa (2060 psia) were determined. From the small scale motor experiments, thrust, C*, Isp, and C* and Isp efficiencies are provided. From these results, mechanistic issues of the combustion process are discussed. In particular, overall lean equivalence ratios that produce flame temperatures near the melting point of alumina resulted in considerably lower experimental C* and Isp efficiencies than equivalence ratios closer to stoichiometric. The infstitution of micron aluminum for nanometer aluminum had little effect on the linear burning rates of Al/ice mixtures for low-mass infstitutions. However, as the mass addition of micron aluminum increased (e.g., beyond 40% 2-μm aluminum in place of 80-nm aluminum), the burning rates decreased. The effects of bimodal aluminum compositions on motor performance were minor, although the experimental results suggest longer combustion times are necessary for complete combustion.

September 2013

DOI: https://www.researchgate.net/publication/269567051_CuOAl_Thermites_for_Solid_Rocket_Motor_Ignition

David A. Reese; Darren M. Wright; Steven Son

Abstract

A safe, fast, repeatable means of ignition is required for lab-scale solid rocket motor test experiments. To prevent early burn data from being obscured, an energetic compound with a high reaction rate is needed. A thermite mixture based on micron copper (II) oxide and micron aluminum was chosen for this purpose. This work investigates the efficacy of CuO/Al thermites for lab-scale rocket motor ignition, including experiments on safety testing, packaging, initiation, igniter size determination, and hot fire testing. The end result is a safe, inexpensive, efficient, and readily available method of igniting lab-scale solid rocket combustors.

July 2011

DOI: https://www.researchgate.net/publication/268479247_Further_Development_of_an_Aluminum_and_Water_Solid_Rocket_Propellant

David E. Kittell, Timothée L. Pourpoint, Lori J. Groven, and Steven F. Son

Abstract

Nanoscale aluminum and water has been used as a stepping stone towards in-situ rocket propellants and as a testbed for nanoenergetic composite propellants. A baseline formulation of nanoscale aluminum and water was developed and demonstrated with a sounding rocket flight in 2009. Performance of the propellant was not optimized, hence a reformulation was sought with an emphasis on improved safety and more efficient combustion. The chosen reformulation is a bimodal powder distribution of 70 wt.% Novacentrix 80 nm Al and 30 wt.% Valimet 2 μm Al at an equivalence ratio of 0.813 (optimized for sea level Isp). The mixture also includes 3 wt.% ammonium dihydrogen phosphate, to inhibit the slow reaction of nanoaluminum with water, and 1 wt.% polyacrylamide to improve material suspension. Ammonium dihydrogen phosphate can protect nanoaluminum in solution for several hours, but degradation can occur while mixing, and pH increases from slightly acidic to basic with increased mixing time and temperature. The stress of mixing might be removing the coating and exposing nanoaluminum to water. It is also shown that nanoaluminum reacts faster in basic aqueous solutions than in solutions with neutral pH. Static motor tests reveal that propellant formulations with neutral pH provide better performance. Implementations of shorter mixing times and reduced temperatures are used to control the pH of the propellant, resulting in increased Isp values of as much as 30%. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Other Universities

October 2020

DOI: https://www.tandfonline.com/doi/abs/10.1080/00102202.2020.1820496?journalCode=gcst20

Frederic Blais, Philippe Julien, Jan Palecka, Samuel Goroshin, Jeffrey M. Bergthorson

Abstract

Measurements of how the flame speed in suspensions of metal fuels depends on the initial temperature of the unburned mixture are important for understanding the role of mixture preheat by radiation heat transfer. This preheat can be an important stabilization mechanism for metal dust flames in energetic devices. A newly constructed counter-flow flat-flame metal dust burner allows for the measurement of burning velocities in aluminum-air suspensions preheated to temperatures up to 524 K using Particle Image Velocimetry (PIV). The experimental method was verified by measuring and comparing burning velocities in preheated methane-air mixtures at different fuel-oxygen equivalence ratios with previous experimental data and theoretical predictions. Whereas the flame speed in methane-air mixtures increases by 2.75 times with an increase in temperature to about 524 K, the flame speed in aluminum-air mixtures increases by less than 2 times over the same temperature interval. The independence of the adiabatic flame temperature of aluminum-air flames on the initial temperature of the mixture suggests practically constant reaction rates either for kinetically- or diffusion-controlled aluminum combustion. Thus, the observed moderate dependence of the aluminum-air flame speed on mixture initial temperature can be explained by a cumulative effect of the increased heat diffusivity, decrease in the amount of heat required to reach the particle ignition temperature, and increased flame sensitivity to preheat due to discrete source effects discussed in recent flame models.

2009

DOI: https://doi.org/10.1016/j.proci.2008.06.205

Patrick Lynch, Herman Krier, Nick Glumac

Abstract

A study of the combustion times for aluminum particles in the size range of 3–11 lm with oxygen, car[1]bon dioxide, and water vapor oxidizers at high temperatures (>2400 K), high pressures (4–25 atm), and oxidizer composition (15–70% by volume in inert diluent) in a heterogeneous shock tube has generated a correlation valid in the transition regime. The deviation from diffusion limited behavior and burn times that could otherwise be accurately predicted by the widely accepted Beckstead correlation is seen, for example, in particles below 20 lm, and is evidenced by the lowering of the diameter dependence on the burn time, a dependence on pressure, and a reversal of the relative oxidizer strengths of carbon dioxide and water vapor. The strong dependence on temperature of burn time that is seen in nano-Al is not observed in these micron-sized particles. The burning rates of aluminum in these oxidizers can be added to predict an overall mixture burnout time adequately. This correlation should extend the ability of mod[1]elers to predict combustion rates of particles in solid rocket motor environments down to particle diameters of a few microns.

June 2017

DOI: https://doi.org/10.1016/j.combustflame.2017.03.006

Michael Soo, Samuel Goroshin, Nick Glumac, Keishi Kumashiro, James Vickery, David L. Frost, Jeffrey M. Bergthorson

Abstract

Imaging emission spectroscopy, spatially resolved laser-absorption spectroscopy, and particle image velocimetry (PIV) are applied to a flat flame stabilized in a suspension of micron-sized aluminum. The results from the combination of diagnostics are used to infer the combustion regime of the particles and to estimate the characteristic combustion time of the suspension. It is observed that the reaction zone of the flame in stoichiometric aluminumair suspensions exhibits strong self-reversal of the atomic aluminum emission lines. These lines also exhibit high optical depths in both emission and absorption spectroscopy. The strong self-reversal and high optical depths indicate high concentrations of aluminum vapor within the reaction zone of the flame at multiple temperatures. These features provide evidence of the formation of vapor-phase micro-diffusion flames around the individual particles in the suspension. In aluminum-methane-air flames, the lack of self-reversal and lower optical depths of the aluminum atomic lines indicate the absence of vapor-phase micro-diffusion flames, and point to a more heterogeneous, and likely kinetically-controlled, particle combustion regime. The reaction zone thickness is estimated from the spatially resolved profiles of aluminum resonance lines in both absorption and emission through the flame. The emission measurements yield a reaction zone thickness on the order of 1.7±0.3 mm in aluminum-air flames, and the absorption measurements yield a thickness on the order of 2.3±0.5. It is demonstrated that the combination of the combustion zone thickness measurement, flame temperatures determined from molecular AlO emission spectra, and particle velocity measurements from the PIV diagnostic permits an estimation of the burning time in the suspension. The burning time in stoichiometric aluminum-air suspensions using the suite of diagnostics is estimated to be on the order of 0.7 milliseconds.

2021

DOI: 10.1016/j.proci.2020.09.017

Jan Palečka, Judy Park, Samuel Goroshin, Jeffrey M Bergthorson

Abstract

This paper introduces a novel Hele-Shaw cell apparatus to be used for the study of propagation and stability phenomena in heterogeneous flames. In particular, the apparatus is used to experimentally examine the coupling/decoupling of dual-front flames propagating in suspensions of micron-size aluminum particles in propane-air gas mixtures at varying gas equivalence ratios and aluminum concentrations. The results show that the thermal coupling that exists between the primary propane-air flame front and the secondary aluminum flame front is a strong function of the rate of reaction, and of the temperature, of the secondary front and much less dependent on the reaction rate or temperature of the primary front. It is also shown that flame instabilities in hybrid aluminum-propane-air flames significantly increase the flame surface area, enhance the propagation rate, and can also exhibit complex interactions with front coupling.

2021

DOI: https://doi.org/10.1016/j.pecs.2022.100994

Samuel Goroshin, Jan Palečka, Jeffrey M. Bergthorson

Abstract

This paper critically reviews the theoretical and experimental literature regarding the fundamental aspects of flames in nonvolatile solid fuel suspensions. Unlike volatile fuels that form continuous premixed gaseous flame sheets, flame fronts in nonvolatile suspensions are driven by heterogeneous reactions localized on the surface, or near the surface, of individual particles. Practically all peculiarities of heterogeneous flames can be linked to this “flame-inside-the-flame” combustion front structure. These localized reactions enable particles to self-heat and transition from kinetically to diffusion-limited heterogeneous reaction during the process of particle ignition. After ignition, burning particles behave as individual diffusion micro-reactors that are insensitive to the bulk gas temperature and overall heat loss from the system. Relatively small quenching distances of the flame in suspensions, long plateaus in the dependence of burning velocity on fuel concentration stretching to very fuel-rich mixtures, and the discrete flame propagation regime, where burning velocity is insensitive to particle combustion time and the flame-front structure is rough and nonuniform, are all manifestations of particle ignition and combustion in the diffusion-limited regime. This review summarizes the key experimental evidence of laminar flame structure and flame speed from a variety of experimental apparatus both in the laboratory and under microgravity conditions, and interprets these results in terms of relatively simple theoretical models. Heterogeneous flames are observed to exhibit many of the thermodiffusive and hydrodynamic instabilities of homogeneous flames, as well as several new instabilities that arise from the multiphase nature of the fuel and particle ignition and extinction. Flames of binary mixtures of heterogeneous fuels, or gaseous and solid fuel mixtures, are also reviewed and it is shown that a simple model based on matching the flame speed between thermally interacting fronts can capture the key physics. Finally, the last chapter of the review discusses why the important or even crucial role of radiation heat transfer predicted by theoretical models for flames in suspensions is not supported by the available experimental evidence. It is argued that large spatial scales of radiation heat transfer do not permit separation of the radiation transfer problem from boundary conditions and flow configuration, making one-dimensional flame models that include radiation inadequate for the description of flames in the laboratory and even in relatively large unconfined dust clouds.

2021

Link: https://escholarship.mcgill.ca/concern/theses/9w032781h

Geoffrey Chase, David Frost

Abstract

The detonation of suspensions of nanometric and flake aluminum powders mixed with aqueous solutions of dilute hydrogen peroxide (H2O2) was experimentally investigated. The nano-Al powder was coated with 8–10 wt% Viton and had a nominal diameter of 91 ± 27 nm. The flake-Al powder was coated with 10 wt% trimethylolpropane trimethacrylate and had a surface area of 5.09 m2/g. Detonation velocity and cylinder wall expansion tests were conducted in aluminum- and PVC-encased charges measured with shock pins and photonic Doppler velocimetry. Mixtures containing aqueous solutions of 10–20 wt% H2O2 detonated at 2.9–3.5 km/s, with variations in the detonation velocity attributed to variations in time-dependent density. Mixtures containing 10 wt% H2O2 solutions did not consistently detonate, indicating that porosity from hydrogen peroxide decomposition has a sensitizing effect. Mixtures containing only distilled water, 5 or 7.5 wt% H2O2 solutions, dilute ammonium nitrate solutions, glass microballoons, or micron-scale spherical aluminum powder failed to sustain detonation, but could potentially sustain detonation with optimization of the shot processing.

April 2022

https://doi.org/10.1364/OL.456342

K. A. Daniel, C. M. Murzyn, D. J. Allen, K. P. Lynch, C. R. Downing, and J. L. Wagner

Abstract

This work advances laser absorption spectroscopy with measurements of aluminum monoxide (AlO) temperature and column density in extreme pressure (P > 60 bar) and temperature (T > 4000 K) environments. Measurements of the AlO A 2Πi–X 2Σ + transition are made using a micro[1]electromechanical system, tunable vertical cavity surface emitting laser (MEMS-VCSEL). Simultaneous emission measurements of the AlO B 2Σ +–X 2Σ + transition are made along a line of sight that is coaxial with the laser absorption. Absorption temperature fits agree with emission spectra for a T =3200 K, P=9 bar case. In cases with T > 4000 K, P > 60 bar, absorption fits match the ambient temperature while emission fits over-estimate it, owing to high optical depths. These data juxtapose passive and active spectro[1]scopic methods and demonstrate the versatility of AlO laser absorption in high-pressure and high-temperature environments where experimental data remain scarce, and engineering models will benefit from refined measurements.

February 2023

DOI: https://doi.org/10.1016/j.combustflame.2022.112532

G. Foster, N.J. Kempema, J.E. Boyer, J.R. Harris, R.A. Yetter

Abstract

Aluminum is an energy-dense metal that reacts exothermically with a range of oxidizers, making it a potentially useful fuel for certain thermal energy and power applications (e.g., boilers, swirl-stabilized burners, rockets, etc.). In addition to its reactive properties, aluminum is naturally abundant and commercially available in fine powders that are relatively inexpensive and chemically stable. Fine aluminum dusts, with particle diameters on the order of micrometers, can be aerosolized and mixed with a gaseous oxidizer such as air to create stable dust flames and heat for a thermodynamic cycle. In order to realize the potential utility of aluminum-air dust flames, the fundamental combustion behavior, such as the burning velocity, must be understood. In this work, an experimental system was developed that allows metal dust flames to be observed within an optically-accessible pressurized chamber. Using a high-speed camera, fuel-rich premixed aluminum-air jet flames were imaged through narrowband interference filters, and the data were used to calculate burning velocity. A single polydisperse size distribution of particles was tested at pressures ranging from 1 to 7.2 bar. Burning velocity was found to decrease with increased pressure (P), with an approximate proportionality to P−0.6 over the range of pressures tested (∼P−0.3 for only the laminar flow conditions). This reduction in burning velocity with increased pressure is hypothesized to occur due to increased oxidizer density along with a decrease in interparticle spacing, which may result in asymmetric particle heating and increased competition for oxidizer.

December 2010

DOI: https://www.sciencedirect.com/science/article/abs/pii/S0032591010003645

Laila J. Jallo, Mirko Schoenitz, Edward L. Dreizin, Rajesh N. Dave, Curtis E. Johnson

Abstract

Surface modification of aluminum powders for the purpose of flow improvement was performed and several samples were prepared. Correlations between the flowability and reactivity for these powders as well as for the initial untreated aluminum powder were established. The powders were characterized using Scanning Electron Microscope (SEM), particle size distribution, angle of repose flowability test, Constant Volume Explosion (CVE) combustion test, and Thermo-Gravimetric Analysis (TGA). The surface modification of micron-sized aluminum powders was done by: (1) dry coating nano-particles of silica, titania and carbon black onto the surface of spherical aluminum powders and (2) chemically and physically altering the surface properties of the same powders with methyltrichlorosilane. All surface modifications improved flowability of the powders. CVE measurements indicate that powders with an improved flowability exhibit improved combustion characteristics if the powder treatment does not add an inert component to aluminum. The TGA results do not show significant differences in the reactivity of various powders. Based on combined flowability and CVE characteristics, the silane modified material gave the best results followed by the powders dry coated with carbon, titania and silica, respectively.

March 2020

DOI: https://doi.org/10.1016/j.combustflame.2020.03.012

Journal: Combustion and Flame 217(18):93-102

Demitrios Stamatis, Elliot Wainwright, Shashank Vummidi Lakshman, Michael S Kessler, Tim Weihs

Abstract

Micron-sized composite particles consisting of an Al-Mg alloy and Zr were produced via mechanical milling. Three different particle chemistries were prepared with varying ratios of the Al-Mg alloy to Zr. In addition, the prepared powders were size selected using mechanical sieves. Explosively launched combustion properties of these powders were independently measured as a function of the particle stoichiometry and particle size. Ignition temperatures were measured utilizing a heated filament experiment while combustion efficiency was characterized by measuring the dynamic pressure produced in a closed bomb in which the powder was explosively dispersed under fixed enthalpy conditions. Commercial Al powder, Valimet H-2, was also tested alongside these materials as a benchmark. High-speed video and thermocouple measurements were also obtained for the closed bomb experiments. We observed an increase in combustion efficiency from 30% to 80-90% in the composite materials compared to the pure Al. Furthermore , reaction products were collected and analyzed by powder x-ray diffraction to gain further insight into combustion efficiency and reaction pathways. We observed significant improvement of combustion under these experimental conditions, including higher quasi-static pressures and higher rates of pressure rise, with composite fuels compared to pure Al, even without a secondary oxidizer additive.

January 2019

DOI: https://www.researchgate.net/publication/330975798_Effects_of_aluminum_composites_on_the_regression_rates_of_solid_fuels

Christian Paravan, Marco Stocco, Simone Penazzo, Juxhin Myzyri, Luigi T. DeLuca and Luciano Galfetti

Abstract

Innovative, mechanically activated Al–polytetrafluoroethylene (PTFE) composites and ammonium perchlorate (AP) coated nano-sized aluminum (C-ALEX) were produced, characterized, and tested as solid fuel additives. The ballistics of fuel formulations based on hydroxylterminated polybutadiene (HTPB) was investigated in a microburner by a time-resolved technique for regression rate ( r f ) data reduction. Both Al-composites show promising results in terms of r f and mass burning rate enhancement. In particular, the C-ALEX showed a percent r f increase over the baseline (HTPB) of 27% at an oxidizer mass flux of 350 kg/(m ² s), without requiring dedicated dispersion procedures. This performance enhancement was nearly constant over the whole investigated range.

January 2006

DOI: 10.1063/1.2263484

Article

David L. Frost, Samuel Goroshin, Jeff Levine, Robert Ripley, and Fan Zhang

Abstract

The critical conditions for the ignition of spherical aluminum particles dispersed during the detonation of long cylindrical explosive charges have been investigated experimentally. The charges consist of packed beds of aluminum particles (Valimet, CA), ranging in size from 3 -115 mum in diameter, and saturated with sensitized liquid nitromethane. The ignition conditions depend on both the charge and particle diameters, which govern the thermal history of the particles as they are dispersed within the conically expanding products. For a given charge diameter, the most reactive particles correspond to an intermediate size (˜55 mum dia). For this particle size, with increasing charge diameter the particle reaction behavior progresses through several distinct regimes: i) no particle reaction, ii) reaction at isolated spots, iii) reaction in distinct radial bands, and iv) continuous reaction of the particle cloud. In each case, a separation between the detonation front and the onset of aluminum reaction is always observed. To determine the point of particle ignition, visible radiation from the charge is recorded, through a slit, with a 3-color pyrometer and with a line spectrometer, with the wavelengths chosen to overlap the AlO emission lines.

Additive Manufacturing

February 2018

Link: https://escholarship.mcgill.ca/concern/theses/1j92g957r

Andrew Walker

Abstract

This work presents the foundation and results of a study of the pulse laser powder bed fusion process (P-LPBF). It focuses on the unique opportunity offered for the additive manufacturing (AM) industry to control the microstructure and mechanical properties of high strength aluminum alloys.

A literature review has been presented covering the topics; additive manufacturing, high strength aluminum alloys, solidification physics, and evaporation phenomena. The work goes on to present results of a P-LPBF processing study of Al-Zn-Mg-Cu and Al-Mg-Si alloys. It was found that as built specimens of 98.0±0.5 Vol% density were achievable for the Al-Zn-Mg-Cu alloy, whereas samples with 99.3±0.4 Vol% density were produced from the Al-Mg-Si alloy.

Solidification microstructures were examined and found to present highly refined second phases with
coarse melt pool regions for both alloys. Quantitative analysis of the solidification behaviour of the Al[1]Zn-Mg-Cu alloy was conducted with the CGM and KGT microstructure development models. It was concluded that neither alloy exhibited significant departure from equilibrium solidification behaviour. The bulk chemical analyses of P-LPBF specimens of each alloy indicated that significant solute loss had occurred. Standard T6 heat treatment procedures were applied to the samples, yielding the expected microstructure and hardness results. The observed hardness of the Al-Zn-Mg-Cu alloy samples were found to fall below the wrought material while Al-Mg-Si alloy samples were able to slightly exceed the wrought properties. Solute loss was identified as the main variable driving this phenomenon. The AA7175 composition was more sensitive to solute loss as it depended more heavily on precipitation strengthening, while AA6061 made significant use of the Hall-Petch hardening mechanism, allowing it to tolerate substantial solute loss while maintaining the desired mechanical properties.

In summary, this work has investigated the microstructural, mechanical, and chemical properties of two solidification crack susceptible aluminum alloys. The findings clearly demonstrate promising results for the feasibility of P-LPBF AM processing of high strength aluminium alloys.

August 2023

DOI: https://doi.org/10.1016/j.msea.2023.145397

Erfan Maleki, Sara Bagherifard, Asghar Heydari Astaraee, Simone Sgarbazzini, Michele Bandini, Mario Guagliano

Abstract

Post-processing methods can be crucial in addressing the associated anomalies of the as-built state of additively manufactured materials. In this study, for the first time, the effects of gradient severe shot peening as a novel mechanical surface treatment, along with other types of shot peening treatments, including conventional, severe, and over shot peening processes were investigated individually and combined with heat treatment on fatigue behavior of hourglass AlSi10Mg samples fabricated by laser powder bed fusion. Detailed experimental characterizations in terms of microstructure, porosity, surface texture, hardness and residual stresses as well as rotating bending fatigue behavior were conducted. The experimental results revealed a significant fatigue behavior improvement after applying gradient severe shot peening treatments due to their remarkable capacity to modulate surface texture, known as a side effect of peening, besides surface layer nanocrystallization, enhanced hardness, and high compressive residual stresses.

July 2023

DOI: https://www.sciencedirect.com/science/article/pii/S0264127523004240?via%3Dihub

S. Nam, E. Simsek, N. Argibay, O. Rios, H.B. Henderson, D. Weiss, E.E. Moore, A.P. Perron, S.K. McCall, R.T. Ott.

Abstract

Al-Ce-based alloys are promising candidates for additive manufacturing (AM) due to their hot-cracking resistance and because they do not require heat treatment to obtain precipitation strengthening. Rapid solidification rates enabled by AM methods can lead to enhanced mechanical properties; however, the strengthening mechanisms over large composition ranges were unclear. Here, combinatorial synthesis by directed-energy deposition (DED) and hardness measurements were used to rapidly map the composition-dependent strength of the ternary Al-Ce-Mg system. Tensile testing and microstructure characterization of selected compositions were performed to elucidate the compositional dependence of the strengthening mechanisms. Al11Ce3 precipitates were present in all cases, and the maximum hardness (1.25 GPa) was measured for the Al-8Ce-10Mg composition. A combination of (i) Hall-Petch strengthening, based on the FCC-matrix-phase cell size; (ii) particle strengthening, based on Al11Ce3 volume fraction and size; and (iii) solid-solution strengthening, based on Mg composition of the matrix phase, were used to account for the measured strengths. Vickers hardness is shown to correlate well with ultimate tensile strength in these alloys, highlighting the value of surface-based techniques for rapid screening.

October 2021

DOI: https://www.researchgate.net/publication/355372952_Short_Heat_Treatments_for_the_F357_Aluminum_Alloy_Processed_by_Laser_Powder_Bed_Fusion

Matteo Vanzetti , Enrico Virgillito, Alberta Aversa, Diego Manfredi, Federica Bondioli, Mariangela Lombardi and Paolo Fino

Abstract

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 ◦C followed by water quenching and subsequently by an artificial aging at 170 ◦C for 2–8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 ◦C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 ◦C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry.

August 2022

Kyle Tsaknopoulos, Caitlin Walde, Derek Tsaknopoulos and Danielle L. Cote

Abstract

Gas-atomized powders are frequently used in metal additive manufacturing (MAM) processes. During consolidation, certain properties and microstructural features of the feedstock can be retained. Such features include porosity, secondary phases, and oxides. Of particular importance to alloys such as Al 6061, secondary phases found in the feedstock powder can be directly related to those of the final consolidated form, especially for solid-state additive manufacturing. Al 6061 is a heattreatable alloy that is commonly available in powder form. While heat treatments of 6061 have been widely studied in wrought form, little work has been performed to study the process in powders. This work investigates the evolution of the Fe-containing precipitates in gas-atomized Al 6061 powder through the use of scanning and transmission electron microscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS). The use of coupled EDS and thermodynamic modeling suggests that the as-atomized powders contain Al13Fe4 at the microstructure boundaries in addition to Mg2Si. After one hour of thermal treatment at 530 ◦C, it appears that the dissolution of Mg2Si and Al13Fe4 occurs concurrently with the formation of Al15Si2M4 , as suggested by thermodynamic models.

September 2020

DOI:  https://www.mdpi.com/1996-1944/13/18/4051

Kyle Tsaknopoulos, Caitlin Walde, Derek Tsaknopoulos, Victor Champagne and Danielle Cote

Abstract

Aluminum 5056 is a work-hardenable alloy known for its corrosion resistance with new applications in additive manufacturing. A good understanding of the secondary phases in Al 5056 powders is important for understanding the properties of the final parts. In this study, the effects of different thermal treatments on the microstructure of Al 5056 powder were studied. Thermodynamic models were used to guide the interpretation of the microstructure as a function of thermal treatment, providing insight into the stability of different possible phases present in the alloy. Through the use of transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), combined with thermodynamic modeling, a greater understanding of the internal microstructure of Al 5056 powder has been achieved in both the as-atomized and thermally treated conditions. Evidence of natural aging within these powders was observed, which speaks to the shelf-life of these powders and the importance of proper treatment and storage to maintain consistent results.

October 2018

DOI: https://www.researchgate.net/publication/328241021_Gas-Atomized_Al_6061_Powder_Phase_Identification_and_Evolution_During_Thermal_Treatment

Kyle Tsaknopoulos, Caitlin Walde, Victor Champagne, and Danielle Cote

Abstract

Metal additive manufacturing processes often use gas-atomized powder as feedstock, but these processes use different methods for consolidation. Depending on the consolidation temperature, secondary phases may be retained during processing, making it important to understand powder microstructure prior to consolidation. Commercial alloy compositions are typically used for these powders because they have been widely studied and qualified; however, the microstructure of the powder form of these compositions has not been studied. This paper aims to understand the commercial Al 6061 powder: how the internal microstructure of the powder differs from wrought both in the as-manufactured and thermally-treated conditions. A specific focus is put on the Mg-rich phases and their morphologies. This was accomplished through transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. Both the size and morphology of the phases in the powder differ greatly from those in the wrought form.

April 2020

DOI: https://link.springer.com/article/10.1007/s13632-020-00641-6

Caitlin Walde, Kyle Tsaknopoulos, Victor Champagne, Danielle Cote

Abstract

Al 7075 is a heat-treatable Al–Mg–Zn alloy widely used in the aerospace industry. Recently, it has found application as feedstock for metal additive manufacturing (MAM). It has been shown that wrought alloy compositions in powder form differ in microstructure and properties from their conventional form. Given this, it is important to understand the microstructure of the powders prior to use in MAM processes. This work studies as-atomized gas-atomized Al 7075 powders and the effect of thermal treatments on microstructure. Extensive electron microscopy revealed the presence of T-phase, Al7Cu2Fe, and Mg2Si in the as-atomized condition. Thermal treatments were performed at 465 °C and 480 °C to homogenize the microstructure; however, S-phase was unexpectedly present in the samples treated at 465 °C. In both 465 °C and 480 °C treatments, T-phase was not fully dissolved after the 60-min treatment. Guided by thermodynamic modeling, these results indicate a shift in local equilibria in these powders.

October 2018

DOI: 10.18689/ijmsr-1000108

International Journal of Material Science and Research 1 (2018) 50-55

A. Bhagavatam, A. Ramakrishnan, V.S.K. Adapa, G.P. Dinda, et al.

Abstract

Additive manufacturing (AM) has become one of the most important research topics with its ability to manufacture a wide range of alloys like steel, nickel-based super alloys, titanium alloys, aluminum alloys, etc. Al 7075 is not a friendly alloy for laser metal deposition (LMD). This paper reports the successful development of LMD process for deposition of defect-free Al 7075 alloy. By preheating the substrate to 260°C the residual stress decreased and eliminated the hot/solidification cracks in the deposit. LMD is a rapid cooling process due to which the gas bubbles of Mg and Zn are trapped in the deposit. These are identified as gas porosity because of the partial evaporation of low boiling point elements like magnesium and zinc present in this alloy. The least porosity observed was 0.08% at 29 J/mm2 of energy input. The SEM and EDS investigation of as-deposited Al 7075 revealed the segregation of Cu, Mg, and Zn rich phases along the inter dendritic regions and grain boundaries. Cu, Mg, and Zn rich phases at the inter dendritic regions dissolved into the α-Almatrix after heat treatment. The XRD scan of laser deposited Al 7075 revealed the presence of Al2CuMg and MgZn2 precipitation hardening phases.

May 2017

DOI: 10.5781/JWJ.2017.35.4.10

Journal of Welding and Joining 35(4)(2017) 67-77.

Singh, A. Ramakrishnan, G.P. Dinda

Abstract

Recently, Al-Si alloys samples have been manufactured at lab scale using various additive manufacturing processes, but so far there is no literature available to investigate the feasibility of fabricating Al-Si alloy component for automotive component applications using Direct Laser Metal Deposition (LMD) technique. This paper deals with the practical challenges of building single wall and block deposition (cuboid shapes) of eutectic Al-Si alloy using direct laser metal deposition process for developing automotive applications. Two scanning pattern, hatch pattern and single wall pattern were chosen to study the effect of scanning direction on mechanical properties as well as microstructural evolution. Microstructural investigation of single wall and block deposition using optical and scanning electron microscopy revealed a 99.9% dense component with very fine hypoeutectic microstructure. Tensile test sample extracted from block deposition showed an impressive elongation of 9% with an ultimate tensile strength of 225 MPa and tensile test sample of single wall showed an average elongation of 9.4% with an ultimate tensile strength of 225 MPa. This investigation revealed that direct laser metal deposition could successfully print the eutectic Al-Si alloy bracket on shock tower hood without any distortion or bending.

May 2012

DOI: 10.1007/s11661-012-1560-3

Microstructural, Metallurgical and Materials Transactions A 44 (2013) 2233-2242.

G.P. Dinda, A.K. Dasgupta, S. Bhattacharya, H. Natu, B. Dutta, J. Mazumder,

Abstract

Direct metal deposition (DMD) technology is a laser-aided rapid prototyping method that can be used to fabricate near net shape components from their CAD files. In the present study, a series of Al-Si samples have been deposited by DMD in order to optimize the laser deposition parameters to produce high quality deposit with minimum porosity and maximum deposition rate. This paper presents the microstructural evolution of the as-deposited Al 4047 sample produced with optimized process parameters. Optical, scanning, and transmission electron microscopes have been employed to characterize the microstructure of the deposit. The electron backscattered diffraction method was used to investigate the grain size distribution, grain boundary misorientation, and texture of the deposits. Metallographic investigation revealed that the microstructural morphology strongly varies with the location of the deposit. The layer boundaries consist of equiaxed Si particles distributed in the Al matrix. However, a systematic transition from columnar Al dendrites to equiaxed dendrites has been observed in each layer. The observed variation of the microstructure was correlated with the thermal history and local cooling rate of the melt pool.

January 2012

DOI: 10.1007/s11661-012-1560-3

Surface and Coatings Technology 206 (2012), 2152-2160.

G.P. Dinda, A.K. Dasgupta, J. Mazumder

Abstract

Laser melting of Al–Si alloys has been investigated extensively, however, little work on the microstructural evolution of laser deposited Al–Si alloys has been reported to date. This paper presents a detailed microstructural investigation of laser deposited Al–11.28Si alloy. Laser aided direct metal deposition (DMD) process has been used to build up solid thin wall samples using Al 4047 prealloyed powder. The evolution of macro- and microstructures of laser deposited Al–Si samples was investigated using X-ray diffraction, optical microscopy, scanning electron microscopy and electron backscattered diffraction techniques. Microstructural observation revealed that the morphology and the length scale of the microstructures are different at different locations of the sample. A periodic transition of microstructural morphology from columnar dendrite to microcellular structure was observed in each layer. The observed difference in the microstructure was correlated with the thermal history of the deposit.

July 2020

DOI: 10.1007/s11663-020-01902-z

Metallurgical and Materials Transactions B volume 51, pages2230–2239 (2020)

M. Skelton, C. V. Headley, E. J. Sullivan, J. M. Fitz-Gerald & J. A. Floro

Abstract

Gas-atomized powders are commonly used in additive manufacturing, specifically laser powder bed fusion, due to their high flowability during recoating. Morphological changes can occur in particles that are irradiated by the laser during additive manufacturing, but are not incorporated into the melt pool. These irradiated particles will affect the rheology of the recycled powder in subsequent builds, potentially leading to failures due to uneven powder flow or spatial distribution. Thus, a better understanding of mechanisms that degrade the sphericity of powder after being laser irradiated is needed. This research examines morphological changes in Al and Al-Cu eutectic powders after laser melting. Two complementary approaches were taken. First, particles found along the edges of line scans following high-power (300 W) laser irradiation were characterized. The collected particles displayed morphological anomalies not observed in the as-received powder. Then, to gain a more quantitative and controlled perspective on morphological evolution, the same base powders were dispersed onto glass substrates and irradiated with a low-power (6.5 W) CW laser diode. This approach, which permits characterization of specific particles before and after laser irradiation, clearly shows laser-induced changes in the surface morphology of particles in the form of dents and rifts. These results suggest that isolated melting and resolidification of particles contained within their respective oxide shells can occur at the relatively low laser energy densities present at the edges of laser melt tracks. Thermal stresses developing in the oxide shell during cooling can account for the observed morphological changes in the context of shell-buckling theory.

Cold Spray and Surface Coating Technology

May 2016

Link: https://escholarship.mcgill.ca/concern/theses/p5547v08p

Hanqing Che, Stephen Yue

Abstract

Carbon fibre reinforced polymer (CFRP) is a very competitive alternative to aluminum for aircraft structures for lightweighting purposes, but this leaves vulnerability against lightning strike. Cold spray is one coating approach to make the polymers lightning strike proof. The aim of this work is to use cold spray on aircraft quality CFRPs to produce a metal coating with sound mechanical properties and good electrical conductivity for lightning strike protection. Copper, aluminum and tin were used as the coating materials and cold sprayed with both a high-pressure and a low-pressure cold spray system. A number of different combinations of the gas pressure and gas preheating temperature were used for the cold spray process. Erosion was found to be the key obstacle to developing continuous coatings on the CFRP substrates with the high-pressure system. On the other hand, continuous tin coatings were successfully obtained on the CFRP with the low-pressure system, due to the very soft tin coating the substrate through a “crack filling” mechanism; a process map was generated to define appropriate cold spray conditions. The tin/CFRP adhesion, which was assessed by pull-off tests, revealed the bonding was mainly mechanical since the adhesion strength was at a low level. Copper, aluminum and zinc powders were mixed with tin with the aim of increasing conductivity, and the addition of copper and zinc led to much higher deposition efficiencies compared to the pure tin coating. To understand, more generally, the cold sprayability of metal powders on polymeric substrates, powders of various compositions and characteristics were sprayed on different polymer substrates. Thermoplastic polymers generally showed positive results; in particular, thick copper coatings were successfully deposited on two thermoplastics. The electrical conductivity of the cold sprayed coatings was measured by the four-point conductivity measurement method. The conductivity in the as-sprayed tin coating was approximately half of that of bulk tin, and increased to 73 per cent as conductive as bulk tin after annealed at 80°C for 72 hours. The addition of copper generally did not increase the overall conductivity due to the growth of the more resistive intermetallics. Last but not least, continuing current injection tests, which duplicated component C of a lightning waveform, were performed on the tin coatings. The results showed that the cold sprayed tin coatings can provide effective protection to the CFRP underneath when subjected to a 100A current.

September 2018

DOI: https://www.sciencedirect.com/science/article/abs/pii/S0257897218307035?via%3Dihub

Tian Liu, Jeremy D. Leazer, Sarath K. Menon, Luke N. Brewer.

Abstract

This work describes the micro- and nanostructures of inert gas atomized Al-Cu alloy powder particles over a range of compositions. For cold spray deposition, the microstructure and elemental distribution within the feedstock powder play a critical role in determining the final microstructure and properties of the fabricated material. A series of Al-Cu binary alloy powders, ranging from 2 to 5 wt% Cu, were produced by inert gas atomization and were then thoroughly characterized using electron microscopy and X-ray diffraction. The gas atomized powder particles, nominally 20 μm in diameter, presented a cellular structure with θ (Al2Cu) phase forming along the cell boundaries. The continuity and phase fraction of the θ phase increased systematically with copper content. No Guinier-Preston zones were observed in the powders, but small, incoherent θ phase particles were observed in the matrix near the cell boundaries. The as-atomized particles were observed to be in a non-equilibrium state with a reduced amount of θ phase and altered lattice parameters for the α and θ phases. A mild, post-atomization annealing returned the θ phase fraction and lattice parameters to their equilibrium values.

July 2018

DOI: Fatigue behavior of freestanding AA2024 and AA7075 cold spray deposits – ScienceDirect

B.C. White, W.A. Story, L.N. Brewer, J.B. Jordon.

Abstract

This paper examines the fatigue properties of freestanding AA7075 and AA2024 Cold Spray (CS) deposits. In this study, high pressure cold spray was used to make deposits large enough to machine mechanical test specimens free from the substrate. To quantify the mechanical performance, monotonic tensile and stress-controlled fatigue experiments were carried out on the freestanding CS and wrought AA7075 and AA2024 specimens. The experimental fatigue results revealed a reduction in the stress-life behavior of the CS deposits compared to the corresponding wrought material. However, when normalized by their ultimate tensile strengths, the CS specimens compared very well with the wrought materials, especially for the CS AA7075. Post-mortem analysis of the CS specimens revealed that fatigue cracks typically initiated from layer interface defects and subsequent crack propagation was influenced by the CS prior-particle boundaries. The results from this study indicate that refining the layer interface bonding may increase the fatigue resistance of freestanding aluminum alloy CS deposits.

October 2010

DOI:10.1016/j.ijfatigue.2020.105744

Sara Bagherifard, Mario Guagliano

Abstract

Cold spray technology has recently gained much attention for applications beyond its primary cause of protective coating deposition. It has found its way for depositing thin films for surface functionalization, thick coatings for geometrical restoration, and has exhibited a high potential for additive manufacturing. As cold spray paves its way towards more structural applications, evaluating its performance under cyclic loading is of significant importance. Herein, the current state of the art on the contribution of various forms of cold spray deposits to fatigue strength is reviewed. Future perspectives for enhancing their structural integrity and promising trends are discussed.

September 2017

DOI:10.1007/s11666-017-0643-5

Klara Petráčková, Jan Kondás, Mario Guagliano

Abstract

Cold-sprayed coatings made of A357 aluminum alloy, a casting alloy widely used in aerospace, underwent set of standard tests as well as newly developed fatigue test to gain an information about potential of cold spray for repair and additive manufacturing of loaded parts. With optimal spray parameters, coating deposition on substrate with smooth surface resulted in relatively good bonding, which can be further improved by application of grit blasting on substrate’s surface. However, no enhancement of adhesion was obtained for shot-peened surface. Process temperature, which was set either to 450 or 550 °C, was shown to have an effect on adhesion and cohesion strength, but it does not influence residual stress in the coating. To assess cold spray perspectives for additive manufacturing, flat tensile specimens were machined from coating and tested in as-sprayed and heat-treated (solution treatment and aging) condition. Tensile properties of the coating after the treatment correspond to properties of the cast A357-T61 aluminum alloy. Finally, fatigue specimen was proposed to test overall performance of the coating and coating’s fatigue limit is compared to the results obtained on cast A357-T61 aluminum alloy.

October 2018

DOI:10.1007/s11661-018-4929-0

Anastasios G. Gavras, Diana A. Lados, Victor K. Champagne, Robert J. Warren, Dileep Singh

Abstract

Cold-spray-processed aluminum alloys have static mechanical properties superior to those of aerospace cast alloys, and similar to those of their wrought counterparts, making them good candidates for structural applications. However, their broad and confident use relies upon systematic fatigue crack growth studies to investigate and demonstrate the materials’ performance in critical high-integrity components. In this work, the fatigue crack growth behavior in early stages (small crack growth regime) was investigated for cold-spray processed 6061 aluminum alloys and coatings, at stress ratio R = 0.1, in room temperature laboratory air. The effects of the characteristic microstructure and initial flaw size on the fatigue crack growth response were systematically examined, and the crack growth mechanisms at the microstructural scale were established and compared to those of long cracks. The mechanical interfacial stability of coatings was examined in cold-spray 6061–rolled 6061-T6 couples. An original method of quantifying the deposition–substrate interfacial strength, and correlating it to the response under cyclic loading via crack-interface stability maps, was developed. The proposed methodology is based on combined scratch testing and fracture mechanics formulations, and failure at the coating–substrate interface can be predicted for any crack growth scenario under cyclic loading. The method can be broadly used for the design and optimization of cold-spray and other coatings, as well as in structural repair.

December 2020

DOI: https://doi.org/10.1016/j.apsusc.2020.147643

Alexis T. Ernst, Peter Kerns, Aaron Nardi, Harold D. Brody, Avinash M. Dongare, Seok-Woo Lee, Victor K. Champagne, Steven L. Suib, Mark Aindow

Abstract

Surface oxides formed on powder feedstocks used for cold spray deposition can play an important role in the bonding of the particles and in the development of defects in the deposit. A combination of scanning transmission electron microscopy and x-ray photoelectron spectroscopy was used to investigate the oxides formed on gas-atomized Al 6061 alloy feedstock powders. The powders were studied in the as-atomized condition and after two different thermal exposures that correspond to typical feedstock pre-treatment conditions. The surface features and internal microstructures are consistent with those reported previously for these powders. The as-atomized powders have 5.2 nm thick amorphous oxide layers, with an outer Mg-rich sub-layer and an inner Mg-lean sub-layer. Powders heat-treated at 230 °C in air exhibit slightly thicker oxide layers with a crystalline MgAl2O4 spinel outer sub-layer and an amorphous aluminum oxide inner sub-layer. Powders homogenized under Ar at 400 and 530 °C have significantly thicker (8.9 nm) oxide layers with evidence for a defect inverse spinel Al(Mg,Al)2O4 inner sub-layer between the MgAl2O4 spinel outer sub-layer and the alloy. Differences between these observations and those reported previously for oxidation of bulk alloys are explained on the basis of Mg surface segregation during the gas atomization process.

October 2020

DOI: https://www.researchgate.net/publication/344900138_Rapidly_Solidified_Gas-Atomized_Aluminum_Alloys_Compared_with_Conventionally_Cast_Counterparts_Implications_for_Cold_Spray_Materials_Consolidation

Bryer C. Sousa, Caitlin Walde, Victor K. Champagne, Aaron T. Nardi, Richard D. Sisson and Danielle L. Cote

Abstract

In this work, three commercially available aluminum alloy systems (Al 2024, Al 6061, and Al 7075) were considered to explicitly capture the differences in material properties associated with a rapidly solidified, gas-atomized particulate feedstock as compared with their conventionally cast counterparts. Differences between the microstructural, thermodynamic, mechanical, and kinetic behaviors associated with gas-atomized and conventionally bulk counterparts have been tacitly assumed by the cold spray community. However, many researchers continue to utilize legacy properties from bulk materials when simulating particle impact phenomena in silico, for example. By way of recognizing the fact that bulk material properties may not serve as substitutes for gas-atomized powder property input parameters for cold spray process simulation and computation in silico, enhanced cold spray research and development will be more easily achieved. Therefore, understanding the feedstock powder characteristics for use in cold spray can lead to fine-tuning the properties of cold spray consolidations. Optical microscopy, scanning electron microscopy, nanoindentation, microhardness, differential scanning calorimetry, elemental analysis, and cooling rate calculations were utilized. This work confirms preliminary findings that powder alloys may not be treated the same way as their bulk counterparts in so far as the enactment of heat treatment processing parameters are concerned. Specifically, vast discrepancies were found in the grain size, secondary phases, and mechanical behavior between the powder and cast versions of each alloy.

January 2020

DOI: Aerospace | Free Full-Text | Mechanical Properties of Cold Sprayed Aluminium 2024 and 7075 Coatings for Repairs (mdpi.com)

Jiawei Kelvin Bi, Zhi Cheng Kelvin Loke, Chi Keong Reuben Lim, Kok Hoon Tony Teng and Pak Keng Koh

Abstract

This study investigates the mechanical properties of aluminium 2024 (Al-2024) and aluminium 7075 (Al-7075) cold-sprayed materials and coatings for repairs. It aims to determine the acceptable data needed to meet regulatory requirement when substantiating cold spray repairs. The study focuses on repairs of non-principal structural element (PSE) structures such as skin and panels that are prone to corrosion and wear. For cold spray repair of such components, the microstructure, tensile, peel, bearing, and bending strength from the repair process and powder materials of Al-2024 and Al-7075, were identified and investigated in accordance with MIL-STD-3021. Results show an average coating porosity of <1.2% for both materials. Average tensile strength was 247.1 MPa (with elongation of 0.76%) for Al-2024 and 264.0 MPa (with elongation of 0.87%) for Al-7075. Al-2024 has an average peel strength of 71.9 MPa, while Al-7075 is at 48.9 MPa. The Al-2024 bearing test specimens gave a maximum load strength before failure of 633.6 MPa, while the Al-7075 gave 762.7 MPa. The bending tests show good flexibility for coating thickness ranges of typical skin and panel parts. The results show that cold spray can be used to restore thickness and oversized hole diameters for Al-2024 and Al-7075 skin and panels. The bearing test conducted in this study has also demonstrated a new test method to determine the bearing load and yield strength of a cold spray-repaired hole in a plate.

November 2017

DOI: https://www.researchgate.net/publication/321118076_Microstructural_Evolution_in_Solution_Heat_Treatment_of_Gas-Atomized_Al_Alloy_7075_Powder_for_Cold_Spray

A.Sabard, H. L. de Villiers Lovelock, T. Hussain

Abstract

Cold gas dynamic spray is being explored as a repair technique for high-value metallic components, given its potential to produce pore and oxide-free deposits of between several micrometers and several millimeters thick with good levels of adhesion and mechanical strength. However, feedstock powders for cold spray experience rapid solidification if manufactured by gas atomization and hence can exhibit non-equilibrium microstructures and localized segregation of alloying elements. Here, we used sealed quartz tube solution heat treatment of a precipitation hardenable 7075 aluminum alloy feedstock to yield a consistent and homogeneous powder phase composition and microstructure prior to cold spraying, aiming for a more controllable heat treatment response of the cold spray deposits. It was shown that the dendritic microstructure and solute segregation in the gas-atomized powders were altered, such that the heat-treated powder exhibits a homogeneous distribution of solute atoms. Micro-indentation testing revealed that the heat-treated powder exhibited a mean hardness decrease of nearly 25% compared to the as-received powder. Deformation of the powder particles was enhanced by heat treatment, resulting in an improved coating with higher thickness (* 300 lm compared to * 40 lm for untreated feedstock). Improved particle– substrate bonding was evidenced by formation of jets at the particle boundaries.

May 2006

DOI: 10.31399/asm.cp.itsc2006p0277

Conference: ITSC2006

A.C. Hall, R.L. Williamson, D.A. Hirschfeld, T.J. Roemer

Abstract

An earlier study reported an investigation of the mechanical properties of cold sprayed aluminum and the effect of annealing on those properties. In that study, cold spray coatings approximately one centimeter thick were prepared using three different feedstock powders: Valimet H-10, Valimet H-20, and Brodmann Flomaster. ASTM E8 tensile specimens were machined from these coatings. Each material was tested in two conditions: as-sprayed and after a 300°C, 22 hour air anneal. The as-sprayed material showed a high ultimate strength and low ductility, < 1% elongation. The annealed samples showed a reduction in the ultimate strength but a dramatic increase in ductility, up to 10% elongation. Microstructural examinations and fractography clearly showed a change in the fracture mechanism between the as-sprayed and annealed material, but insufficient data was available to conclusively explain the ductility increase at that time. Since then, Kikuchi mapping of the Valimet H-10 material in the as-sprayed and annealed conditions has been conducted. Kikuchi mapping allows indexing of grains, identification of grain boundaries, and phase identification using backscattered diffraction patterns in an SEM. The data shows that significant recrystallization within the splats upon annealing has occurred. No significant crystal growth across splat boundaries is observed. The data demonstrate that the mechanism of ductility increase in annealed cold spray deposits is recrystallization of the base aluminum material.

January 2006

Journal: Journal of Thermal Spray Technology 15(2):233-238 Follow journal

DOI: 10.1361/105996306X108138

A. C. Hall, D. J. Cook, R. A. Neiser, T. J. Roemer, D. A. Hirschfeld

Abstract

Cold spray, a new member of the thermal spray process family, can be used to prepare dense, thick metal coatings. It has tremendous potential as a spray-forming process. However, it is well known that significant cold work occurs during the cold spray deposition process. This cold work results in hard coatings but relatively brittle bulk deposits. This work investigates the mechanical properties of cold-sprayed aluminum and the effect of annealing on those properties. Cold spray coatings approximately 1 cm thick were prepared using three different feedstock powders: Valimet H-10: Valimet H-20: and Brodmann Flomaster. ASTM E8 tensile specimens were machined from these coatings and tested using standard tensile testing procedures. Each material was tested in two conditions: as-sprayed; and after a 300°C, 22h air anneal. The as-sprayed material showed high ultimate strength and low ductility, with <1% elongation. The annealed samples showed a reduction in ultimate strength but a dramatic increase in ductility, with up to 10% elongation. The annealed samples exhibited mechanical properties that were similar to those of wrought 1100 H14 aluminum. Microstructural examination and fractography clearly showed a change in fracture mechanism between the as-sprayed and annealed materials. These results indicate good potential for cold spray as a bulk forming process.

November 2010

Link:  https://www.researchgate.net/publication/330873533_Residual_Stress_and_Corrosion_Resistance_of_Aluminium_Coatings_Deposited_by_Cold_Spray_Magnesium_Alloy_AZ_91_Steel_Fe37_0_h_Spray-Salt_Test_300_h_Spray-Salt_Test_1000_h_Spray-Salt_Test_Microstructure_

Project: Cold spray coating and technology

Silvano Rech, A. Trentin, Simone Vezzù, S. Pozza, D. Magalini, L. Tecchio

Abstract

Residual stress by curvature method. Square aluminium alloy (AA6061) substrates were coated in order to perform MLRM and XRD stress characterizations. The coatings were characterized in terms of microstructure, microhardness an porosity. Finally standard spray-salt test has been performed in order to study the corrosion protection of the aluminium Al104-3 coating on two different substrates: carbon structural steel Fe37 and magnesium alloy AZ91. The cold spray deposition process Cold Gas Dynamic Spray or simply Cold spray, is gaining more interest than conventional thermal spray techniques primarily because of the lower deposition temperature required to deposit metallic and composite coatings. Cold spray does not use a heat source, such as the conventional thermal spray processes, but instead uses a high-pressure gas jet to accelerate particles to supersonic speed through a convergent-divergent de Laval nozzle so that the particles achieve sufficient kinetic energy to undergo plastic deformation on impact. The main part of the gas flows through a heating system while a minor part of the gas goes through the powder feeder and drags the particles to the nozzle. The two flows come together at the entrance of the nozzle and they are accelerated to supersonic speed thanks to the geometry of the nozzle. The gas temperature ranges typically between 200 and 800 °C but the particle temperature is highly slower because of the very short time in which they get in contact with the gas so the cold spray process does not involve bulk melting and the material is mostly produced entirely in the solid state. Conclusions 1. High particles deformation and low porosity content indicate a good cohesion in coating 2. Hardening of deposited particles; there are no difference between the three powders 3. Stresses inside coating are compressive 4. Aluminium coating exhibit after 1000h of spray-salt test a good protection of Mg alloy (AZ91) and carbon steel (Fe37) substrates; passivate coating surfaces show no evident defect and no exhibit delaminations Experimental procedure For this study three different aluminium commercial (Praxial Al 104-3, Sultzer-Metco 54NS, Valimet H15) powders were used. The depositions were carried out by means of CGT-Kinetics 3000 Cold Spray system provided with the special polymeric nozzle designed for aluminium powder spraying. The distance between nozzle and substrate was 20 mm; the powder flow and carrier gas flow rates were kept constant for all depositions. The cold spray gas parameters were kept constant: the nitrogen stagnation temperature was 350 °C and the stagnation pressure was 2.5 MPa. The coatings were deposited on aluminium alloy (AA6061) Almen strips in order to evaluate the Residual stress analysis Almen Almen XRD XRD XRD MLRM MLRM 0 10 20 30 40 50 60 70 80 90 100 Al 104-3 54NS H15 compressive stress intensity [MPa] Stress values are independent of different powders Depth profile on Multipass coating Two of the three stress measurement techniques are comparable except MLRM method that shows higher values due to different layer removing methods Two tensile peeks are exactly on the interface between subsequent cold spray passes Almen strip Curvature XRD MLRM Measurement techniques Cold spray technique induces compressive stresses Magnesium alloy AZ 91 substrate Steel Fe37 substrate polished as dep polished as dep 0 h Spray-Salt Test Corrosion protection In all the samples tested the aluminium coatings passivate and the surface coatings appear similar to that of bulk aluminium. Corrosion resistance is sensible to surface roughness; two different coating finishing are tested: as deposited (R=14.65±3.63mm) and polished (Ra<0.31±0.02mm) Al 104-3 powders 54NS powders H15 powders q Gas atomized powders q Spherical particles with some satellites q Dendritic microstructure with sub-micrometric porosity Cold Spray deposition Average velocity of particles 700 m/s Temperature of powders < 200°C q Good interlocking coating-substrate and very low interface porosity q Particle microstructure was preserved due to low temperature deposition q Higher deformation for the larger mean diameter particles q Low oxygen content (< 0.1%vol) Al 104-3 coating, etched 54NS coating, etched H15 coating, etched Aluminium coatings 0 0,5 1 1,5 2 2,5 3 3,5 Al 104-3 54NS H15 areal porosity[%] Coating Porosity Lower porosity due to high deformation ratio and absence of smaller particles powder powder powder coating coating coating 0 10 20 30 40 50 60 70 80 Al 104-3 54NS H15 hardness [Vickers 5g] Coating Vickers Microhardness q Constant along coating thickness q Coating hardness is about twice higher than particles hardness q Hardening due to high particle deformation q Microhardness independent of powder type Hardness [HV0.005] Advantages: fast, Cheap Disadvantages: accuracy, need model to quantify Advantages: relatively fast, depth profile Disadvantages: need to know coating mechanical properties Advantages: non-destructive, depth profile, local investigation area Disadvantages: need coating mechanical properties, local investigation area and little penetration Cold spray coatings (Al 104-3 powder) Cold Spray gun With de Laval nozzle Porosity is equal to about 2-3% for Al104-3 and H15 coating Porosity is lower than 1% for 54NS coating.

Hydrogen production

July 2022

Link: https://escholarship.mcgill.ca/concern/papers/z603r355s?locale=en

Jenny Kim, Jeffrey Bergthorson

Abstract

An analytical investigation of a novel alternative fuel source, aluminum powder, for its reactive properties upon reaction with water. Extensive research has been performed over the years studying metal-water reactions for their heat generation and in-situ hydrogen production. Both theoretical and experimental studies have focused on determining the effect of parameters such as the type of metal, metal-to-water ratio, activation method, particle size, and temperature of the reaction. However, few have explored the implementation of such fuel in a power generation device. This work explores the use of aluminum-water reactions to power three different Siemens engines of varying power outputs: two industrial engines- RB211 (33 MW) and Trent 60 (66 MW) and one heavy duty gas turbine- SGT5-4000F (329 MW). The thermodynamics cycle is proposed, and analysis is performed to determine the required reactor size. Then, a life cycle carbon emission of aluminum-water fuel is analyzed and evaluated against that of natural gas – the fuel currently used in the three engines.

April 2022

DOI: https://pubs.rsc.org/en/content/articlelanding/2022/RA/D2RA01231F

Keena Trowell, Sam Goroshin, David Frost, Jeffrey Bergthorson

Abstract

Aluminum particles, spanning in size from 10 μm to 3 mm, were reacted with varying densities of water at 655 K. The density of the water is varied from 50 g L−1 to 450 g L−1 in order to understand the effect of density on both reaction rates and yields. Low-density supercritical water is associated with properties that make it an efficient oxidizer: low viscosity, high diffusion, and low relative permittivity. Despite this, it was found that the high-density (450 g L−1) supercritical water was the most efficient oxidizer both in terms of reaction rate and hydrogen yield. The 10 μm powder had a peak reaction rate of approximately 675 cmH23 min−1 gAl−1 in the high-density water, and a peak reaction rate below 250 cmH23 min−1 gAl−1 in the low- and vapour-density water. A decline in peak reaction rate with decreasing water density was also observed for the 120 μm powder and the 3 mm slugs. These findings imply that the increased collision frequency, a property of the high-density water, outpaces reduction in the reaction enhancing properties associated with low-density supercritical water. Hydrogen yield was minimally affected by decreasing the oxidizer density from 450 g L−1 to 200 g L−1, but did drop off significantly in the vapour-density (50 g L−1) water.

December 2014

DOI: https://www.researchgate.net/publication/269576985_Comparative_reactivity_of_industrial_metal_powders_with_water_for_hydrogen_production

Yinon Yavor, Sam Goroshin, Jeffrey M. Bergthorson, David L. Frost

Abstract

The in-situ production of hydrogen from a metal-water reaction resolves some of the main obstacles related to the use of hydrogen as an alternative fuel, namely storage and safety. In this study, experiments are conducted in a batch reactor with sixteen different commercially-available industrial metal powders, with water temperatures ranging from 80 to 200 _C. The hydrogen production rate, total yield, and reaction completeness are determined for each metal-powder fuel and reaction temperature. Aluminum powder produces the largest amount of hydrogen per unit mass throughout the temperature range, followed by the magnesium powder. Manganese powder, which produces the largest amount of hydrogen per unit volume at high temperatures, exhibits a sharp increase in yield between 120 and 150 _C, suggesting the existence of a critical energetic threshold. The aluminum and magnesium powders exhibit high reaction rates, and together with the manganese powder, appear to be the most attractive candidates to serve as fuels for in-situ hydrogen production.

Red woods and other trees on the South-East corner of the VALIMET Orchard.

There are similarities between growing trees and growing a library: the value of the collection grows in time; a wise selection of items is essential. As Aby Warburg used to say, “the key criterion to order books in a library is that of good neighbors”. Any garden designer would agree with that mindset, which is the same we try to follow in this Literature page.

We look forward to serving you!