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.

Cold Spray and Surface Coating Technology

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

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

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.

Combustion Technology

March 2020

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

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

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 2006

DOI: 10.1063/1.2263484

Article

David Frost, 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.

July 2011

DOI: 10.2514/6.2011-6137

Conference: 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit

David E. Kittell, Timothee Pourpoint, Lori Groven, Steven 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. All rights reserved.

Additive Manufacturing

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.

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

We look forward to serving you!