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.
Works co-authored by VALIMET Technology Manager Ian McCarthy
High Frame Rate Analysis Of The Spray Cone Geometry During Close-Coupled Gas Atomization
(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
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
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
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.
Rapid prototyping of close-coupled atomiser components using an analogue atomiser and high frame-rate analysis
Rapid prototyping of close-coupled atomiser components using an analogue atomiser and high frame-rate analysis | Request PDF (researchgate.net)
I.N. McCarthy, N.J.E. Adkins, R.F. Cochrane, A.M. Mullis
High speed imaging and Fourier analysis of the melt plume during close coupled gas atomisation
(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
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
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
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.
Log-Normal Melt Pulsation in Close-Coupled Gas Atomization
(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
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
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
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.
Combustion of explosively dispersed Al-Mg-Zr composite particles
Journal: Combustion and Flame 217(18):93-102
Demitrios Stamatis, Elliot Wainwright, Shashank Vummidi Lakshman, Michael S Kessler, Tim Weihs
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.
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
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.
Critical Conditions for Ignition of Aluminum Particles in Cylindrical Explosive Charges
David Frost, Fan Zhang
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.
Further Development of an Aluminum and Water Solid Rocket Propellant
Conference: 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit
David E. Kittell, Timothee Pourpoint, Lori Groven, Steven Son
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. All rights reserved.
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
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.
Evolution of Fe-Rich Phases in Thermally Processed Aluminum 6061 Powders for AM Applications
Kyle Tsaknopoulos, Caitlin Walde, Derek Tsaknopoulos and Danielle L. Cote
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.
Characterization of Thermally Treated Gas-Atomized Al 5056 Powder
Kyle Tsaknopoulos, Caitlin Walde, Derek Tsaknopoulos, Victor Champagne and Danielle Cote
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.
Gas-Atomized Al 6061 Powder: Phase Identification and Evolution During Thermal Treatment
Kyle Tsaknopoulos, Caitlin Walde, Victor Champagne, and Danielle Cote
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.
Phase Transformations in Thermally Treated Gas Atomized Al 7075 Powder
Caitlin Walde, Kyle Tsaknopoulos, Victor Champagne, Danielle Cote
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.
Laser Metal Deposition of Aluminum 7075 Alloy
International Journal of Material Science and Research 1 (2018) 50-55
A. Bhagavatam, A. Ramakrishnan, V.S.K. Adapa, G.P. Dinda, et al.
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.
Fabrication of Al-11.2Si Components by Direct Laser Metal Deposition for Automotive Applications
Journal of Welding and Joining 35(4)(2017) 67-77.
Singh, A. Ramakrishnan, G.P. Dinda
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.
Characterization of Laser Deposited Al 4047 Alloy
Microstructural, Metallurgical and Materials Transactions A 44 (2013) 2233-2242.
G.P. Dinda, A.K. Dasgupta, S. Bhattacharya, H. Natu, B. Dutta, J. Mazumder,
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.
Evolution of microstructure in laser deposited Al–11.28%Si alloy
Surface and Coatings Technology 206 (2012), 2152-2160.
G.P. Dinda, A.K. Dasgupta, J. Mazumder
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.
On the Morphology Changes of Al and Al-Cu Powder After Laser Melting
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
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
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
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.
Mechanical Properties of Cold Sprayed Aluminium 2024 and 7075 Coatings for Repairs
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
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.
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
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.
Mechanisms Resulting in Improved Ductility of Cold Spray Coatings after Annealing
A.C. Hall, R.L. Williamson, D.A. Hirschfeld, T.J. Roemer
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.
The Effect of a Simple Annealing Heat Treatment on the Mechanical Properties of Cold-Sprayed Aluminum
Journal: Journal of Thermal Spray Technology 15(2):233-238 Follow journal
A. C. Hall, D. J. Cook, R. A. Neiser, T. J. Roemer, D. A. Hirschfeld
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.
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 and mechanical properties Aluminium powders
Project: Cold spray coating and technology
Rech, Silvano & Trentin, A. & Vezzù, Simone & Pozza, S. & Magalini, D. & Tecchio, L.
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.
Comparative reactivity of industrial metal powders with water for hydrogen production
Yinon Yavor*, Sam Goroshin, Jeffrey M. Bergthorson, David L. Frost
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.