Cold Spray Deposition Process Research Articles

Combinatorial synthesis of AlNi alloys by low-pressure cold spray deposition and post-laser alloying process

Aluminum-Nickel (AlNi) alloys are of great interest due to their exceptional high-temperature wear and corrosion resistance, making them valuable in transport, energy, and materials processing applications. However, challenges in the production and shaping of these alloys, particularly as thick coatings, remain significant. This study introduces an innovative method for the high-throughput synthesis of AlNi coatings, utilizing a two-step process: low-pressure cold spray deposition followed by laser surface alloying. The combination of these two techniques not only improves the synthesis process but also opens avenues for exploring new material compositions with specific application requirements. This approach holds significant potential for accelerating the development and optimization of advanced coatings and multiphase compounds in applications such as repair and additive manufacturing.Aluminum and nickel powders were co-sprayed to create coatings with controlled compositions ranging from 50Al50Ni to 10Al90Ni (wt%). Subsequent laser treatment induced in-situ alloying and homogenization, resulting in dense, uniform AlNi coatings. The microstructure and chemical composition were characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), while X-ray Diffraction (XRD) identified the formation of various phases, including Al3Ni and AlNi3 phases. The process demonstrated effective alloying and microstructural homogeneity, with residual alumina present at the surface. Despite the presence of some microstructural defects, such as cracking, this method provides a robust foundation for further refinement and opens new possibilities for tailoring alloy properties through combinatorial cold spray and laser alloying techniques.

Multi-parameter coupled optimization of Al6061 coating porosity based on the response surface method

The objective of this study is to study the multi-particle deposition process of cold spray through numerical simulation methods and to use multi-factor coupling to optimize the porosity of Al6061 coating to more accurately characterize the real cold spray deposition process. This study aimed to predict and optimize the porosity of Al6061 coatings using numerical simulation methods. The tasks to be solved are: to nest the multi-particle model established by the Python script in the CEL deposition model to simulate the cold spray deposition process. A multi-parameter function with particle temperature, substrate temperature, and particle velocity as independent variables and Al6061 coating porosity as dependent variables was established. The response surface analysis method was used to predict the optimal spraying parameters and coating porosity of Al6061 coating. The methods used are as follows: optimize the porosity of the coating through multi-factor coupling through response surface analysis; use a multi-particle model established through a Python script to be nested in the CEL deposition model to simulate the deposition process of cold-sprayed Al6061 multi-particles. To characterize the coating porosity more accurately, the average value of multiple groups of samples was taken as the final coating porosity value. Conclusions. the porosity value of Al6061 coating obtained by the prediction model is 1.969%; Under the influence of multi-factor coupling, particle velocity has the greatest impact on the porosity of the Al6061 coating, and the substrate temperature has the least impact. Optimum spraying parameters: particle temperature 649.692K, substrate temperature 536.437K, and particle velocity 672.385m/s. Under the optimal spraying parameters, the porosity value of the Al6061 coating is 1.91875%; The error between the predicted value and the actual value obtained by numerical simulation is only 2.55%.

Preferential Corrosion in Cold Sprayed Cu Induced by Oxide Inclusions

Cold spray (CS) deposition is a solid-state deposition technique that finds applications in additive manufacturing, coating, and repairing damaged components. During the cold spray deposition process, feedstock particles are accelerated by compressed gas and impinged onto the substrate at high velocity. Bonding between particles and the surface being coated is established by the high kinetic energy released during collision rather than by added thermal energy. As the particles remain in the solid state during spraying, oxidation is minimized. Despite the partial removal of the native air-formed oxides by the jetting effect, residual oxide debris often remains along the particle boundaries within the sprayed objects as inclusions [1]. The oxide inclusions have attracted attention concerning their influence on the inter-particle bonding strength in the deposit [2]. However, little is known about whether they affect the material’s corrosion behavior.In this work, we report a preferential corrosion phenomenon observed in a CS Cu-diluted HNO3 system that is caused by the remaining oxide inclusions. A mechanism that integrates Cu-NO3 – catalytic corrosion cycles with confined geometry resulting from the dissolution of the oxide inclusions is proposed. Furthermore, we find that this corrosion phenomenon may be mitigated through microstructure engineering. Annealing the CS Cu at 600 °C consolidated the oxide inclusions with their distribution changed from continuous thin films to isolated spherical particles [3]. The propagation of the preferential corrosion is hence interrupted by the lack of interconnected pathways. Counterintuitively, Cl– can function as an inhibitor for this preferential corrosion. Preferential corrosion did not initiate when 1 mM Cl– was initially present in the solution and slowed down when Cl– was added after the preferential corrosion occurred. Reference [1] S. Yin, X. Wang, W. Li, H. Liao, H. Jie, Deformation behavior of the oxide film on the surface of cold sprayed powder particle, Applied Surface Science, 259 (2012) 294-300.[2] Y. Ichikawa, R. Tokoro, M. Tanno, K. Ogawa, Elucidation of cold-spray deposition mechanism by auger electron spectroscopic evaluation of bonding interface oxide film, Acta Materialia, 164 (2019) 39-49.[3] J. Tam, B. Yu, W. Li, D. Poirier, J.-G. Legoux, J.D. Giallonardo, J. Howe, U. Erb, The effect of annealing on trapped copper oxides in particle-particle interfaces of cold-sprayed Cu coatings, Scripta Materialia, 208 (2022) 114333.

A hybrid computational approach for modeling cold spray deposition

Cold spray (CS) is a cold-state technology that uses high-velocity supersonic gas flow to propel and deposit powder particles onto a substrate surface. The design and optimization of the cold spray deposition process were recently achieved via the experimental trial-and-error approach, which is laborious and costly. The present study presents a computationally efficient hybrid method for simulating cold spray coating deposition, applied explicitly to Ni coating used for wear applications. The model effectively synergizes meshless and meshed computational schemes in predicting the thermo-mechanical deformation of the impacting Ni particles and SS304 steel substrate. During the simulations, the point cloud (PC) of deformed particle domains is converted into a high-quality finite element (FE) mesh with novel PC processing algorithms. The simulations are carried out for various particle characteristics and spraying conditions. The numerical predictions are validated by comparing them with other numerical schemes and previous experimental studies. The main results indicate that the kinetic energy and morphology of the impacting Ni particles strongly influence plastic deformation and temperature rise in the substrate and predeposited coating particles. Plastic deformation is more prominent at the particle edges and mating material interfaces. At the same time, the temperature rise does not reach the melting point but can allow for recrystallization near highly localized regions of the coating microstructure, even at lower deposition rates. Compressive residual stresses are also observed across the coating and substrate layers, with a non-uniform and nonlinear residual stress field due to complex interactions among neighboring particles. The study aims to provide a robust numerical framework for designing and optimizing cold spray deposition parameters for industrial coatings, bridging the knowledge gap and enabling efficient and cost-effective simulations for process optimization.

Cold spray manufacturing of oxide-dispersion strengthened (ODS) steels using gas-atomized and ball-milled 14YWT powders

The cold spray deposition process has been investigated for the manufacture of 14YWT oxide-dispersion strengthened (ODS) steel, a nanostructured ferritic alloy (NFA), using gas-atomized and ball-milled feedstock powders. Cold spraying of the gas-atomized powder resulted in a thick dense deposit, but annealing them above 900 °C induced grain growth and heterogeneous precipitation of nanoparticles, thus resulting in lower hardness (∼ 170 HV) compared to 14YWT ODS steel manufactured by the conventional method. The ball-milled powder (Fe-14Cr-3W-0.4Ti-0.2Y-0.125O) was cryomilled in liquid N2 to achieve small particle sizes followed by annealing in a H2/Ar environment at 1000 °C and 1100 °C to reduce the hardness from ∼ 8 GPa to ∼ 5 GPa. Both smaller particle sizes and lower hardness of annealed powders made them amenable to the cold spray deposition process, resulting in thick and dense deposits, while retaining the favorable fully solutionized microstructure of the ball-milled powders. The microstructure of the as-deposited ODS exhibited very fine grain sizes (50–250 nm) with a uniform dispersion of Y-Ti-O nanoprecipitates in the ferritic steel matrix. The hardness values of the cold spray deposits using the powders annealed at 1000 °C and 1100 °C was 770 HV and 496 HV, respectively. Post-heat treatment of the as-deposited material up to 1100 °C showed a high-density microstructure with uniformly dispersed nanoscale oxide particles. The hardness of the annealed deposits up to 1000 °C had a notably higher hardness than bulk 14YWT ODS steel manufactured by conventional methods. The study demonstrates that cold spray deposition of the microstructurally-tailored feedstock powders can be used to successfully manufacture ODS steel with microstructure and properties comparable to those produced by the conventional methods, while providing for an attractive option for the more rapid and cost-effective manufacturing of ODS steel cladding tubes.

Additional hindrances to metallurgical bonding from impurities during microparticle impact

Successful cold spray processing requires the formation of metallurgical bonds at the interface between particle impact sites and the substrate. While surface contamination on either the particle or substrate can interfere with metallurgical bonding, the details of particle/substrate interface chemistry are usually obscured or lost during the nanoseconds-long particle impact process. To provide a direct, detailed account of particle-substrate interfacial chemistry, we perform post-mortem scanning transmission electron microscopy and spectroscopy of impact sites of single copper microparticles, launched with a laser-induced particle impact tester, on a copper substrate. In addition to native oxides, we find that amorphous carbon and spherical copper oxide dispersoids are also present near/at the interface. Further, these features are found to influence metallurgical bonding. These results offer additional considerations for optimizing the quality of the cold spray deposition process.

Cold sprayed Cr-coating on Optimized ZIRLO™ claddings: the Cr/Zr interface and its microstructural and chemical evolution after autoclave corrosion testing

Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray deposition process is studied. Microstructure and chemistry of this material are investigated before and after exposure to autoclave corrosion testing with scanning electron microscopy, energy dispersive spectroscopy analysis, electron backscattered diffraction, transmission electron microscopy and atom probe tomography. The results are used to assess what changes have occurred upon autoclave exposure. The formation of a compact, 80 – 100 nm thick Cr2O3 layer is observed on the surface of the exposed samples. Nucleation of ZrCr2 intermetallic phase is discovered at the Cr/Zr interface. This Laves phase nucleates inside the intermixed bonding layer that can be found in both pristine and exposed samples, and decorates the interface in the form of small particles (less than 50 nm in size). Using transmission electron microscopy and atom probe tomography the growth of a Zr-Cr-Fe phase was detected. This phase is found in the region of the Zr-substrate immediately adjacent to the coating, up to a few hundred nanometres distance from the Cr/Zr interface. A small degree of recrystallization occurs upon autoclave exposure in the 1-2 µm thick nanocrystalline layer produced on the Zr-substrate by the cold spray deposition method utilized for the fabrication of the Cr-coating.

Influence of the deposition parameters on the tribological behavior of cold gas sprayed FeMnCrSi alloy coatings

Cold Spray deposition process may be an alternative for the High-Velocity Oxy-Fuel (HVOF), providing high kinetic energy without particles oxidation. In this work, an FeMnCrSi alloy was deposited onto carbon steel substrate by Cold Gas Spray (CGS) process varying spraying parameters (working gas, its pressure and temperature). Cavitation resistance was evaluated by ultrasonic cavitation testing, and the sliding wear resistance was studied by ball on disk testing, with intent to understand the behavior of this coating when exposed to sliding wear condition. FeMnCrSi sprayed using N2 working gas at 1000 °C showed higher hardness, elastic modulus, cavitation resistance, and sliding wear resistance than FeMnCrSi deposited with 900 and 1100 °C. The samples deposited with N2 at 1000 °C and He at 600 °C showed higher compressive residual stress and flatenning ratio also. The tests were performed for CGS sprayed 316 L stainless steel, which is used as a benchmark material.

On the Influence of Manufacturing Strategy of 3D-Printed Polymer Substrates on Cold Spray Deposition

PMCs are anisotropic and heterogeneous structures with excellent performances in terms of mechanical strength and stiffness, coupled with reduced weight, widely used in engineering sectors. The use of PMCs can be further extended by improving their surface properties such as electrical conductivity, erosion, radiation and lightning protection. In this context, the surface metallization seems to be best solution. In particular, the cold spray (CS) technique candidates as a potential method for the manufacturing of a metal coating on PMCs’ surface. However, the design and the manufacturing methods of PMCs can play a crucial role for an effective metallization through CS. The additive manufacturing technologies for composite materials can be used to manufacture customized reinforced polymer-based panels, like PMCs; the most common method for printing them is the Fused Filament Fabrication (FFF) technique which relies on the thermal extrusion of a thermoplastic feedstock from a mobile heated nozzle. Therefore, this research activity aims to manufacture customized PMCs panels by using FFF technology for the substrate and the cold spray technique for the metallization in order to study the influence of the substrate manufacturing strategy on CS deposition process. For this purpose, three kind of 3D-printed PMCs were manufactured through the FFF technology by varying the percentage fill of the Onyx polymeric matrix and aluminum powders were sprayed on the substrates with a low-pressure cold spray (LPCS) system; both FFF and CS process parameters were varied to study the process in its wholeness. Microscope analyses were carried out to analyze the influence of the manufacturing strategy on the coating quality.

Characterization of as-deposited cold sprayed Cr-coating on Optimized ZIRLO™ claddings

As-produced Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray (CS) deposition process is studied. Cross-sectional electron microscopy, nano-hardness profiling, transmission electron microscopy, transmission Kikuchi diffraction, and atom probe tomography (APT) were performed to investigate the nature of the CS Cr-coating/Optimized ZIRLO™ interface, the microstructure of the coating, and the effects of the deposition on the Zr-substrate microstructure. The former surface of the Zr-substrate was found to have a highly deformed nano-crystalline microstructure, the formation of which was attributed to dynamic recrystallization occurring during coating deposition. This microstructural change, evaluated with electron backscattered diffraction and nano-hardness profiling, appeared to be confined to a depth of a few microns. Through APT analysis, a 10–20 nm thick intermixed bonding region was observed at the interface between coating and substrate. The chemical composition of this region suggests that this layer originated from a highly localized shearing and heating of a thin volume of the outermost former surface of the substrate. The study of the intermixed bonding region's crystalline structure was performed with high resolution transmission electron microscopy and revealed a distorted hexagonal close-packed structure.

Particle–Substrate Transient Thermal Evolution During Cold Spray Deposition Process: A Hybrid Heat Conduction Analysis

A hybrid analytical heat conduction model was developed to predict the transient thermal evolution at the particle–substrate interface during the deposition of cold spray process. First, three-dimensional heat conduction model based on classical diffusion approach was developed to predict the transient surface temperature of the substrate. To that end, the traveling wave solution technique was utilized in order to take into account the effect of the movement of the cold spray nozzle. The results of the analytical model were validated with the experimentally measured surface temperature which was obtained by employing a low-pressure cold spray unit to generate the impingement of a compressed air jet on a flat substrate. The analytical model was further utilized to investigate the effect of the non-dimensional characteristic velocity of the traveling heat source on the surface temperature profile of the substrate. It was found that both the maximum surface temperature and the spatial variation of surface temperature profile of the substrate decreased as the non-dimensional characteristic velocity increased. The mathematical model was further extended by developing a one-dimensional hyperbolic (non-Fourier) heat conduction model to predict the temperature rise at the particle–substrate interface during the cold spray deposition process. In order to validate the results of the hybrid model, a three-dimensional finite element model was developed in ABAQUS to simulate the thermal and dynamic behavior of a single particle upon impact. The results of the hybrid analytical model for the temperature at the particle–substrate interface were compared to the results of the numerical model, and good agreement was found. It was concluded that by coupling the classical diffusion theory and hyperbolic heat conduction approach, the proposed hybrid analytical model can be utilized to predict the transient temperature of the particle–substrate interface during the cold spray deposition process a priori before experimentation.

Cold spray deposition of 304L stainless steel to mitigate chloride-induced stress corrosion cracking in canisters for used nuclear fuel storage

A feasibility study of the cold spray deposition process of 304L stainless steel on 304 stainless steel substrates as a mitigation method for chloride-induced stress corrosion cracking (CISCC) has been investigated under various substrate conditions. The study is aimed at the application of this technology to mitigate CISCC that may potentially occur in or near the fusion welded regions of stainless steel canisters in Dry Cask Storage System (DCSS) for used nuclear fuels. Spherical gas-atomized 304L stainless steel powder, in the size range of 25 μm–44 μm, was used as feedstock powder for the cold spray process. The powder was deposited on 304 substrates with various surface conditions: as-polished, oxidized, cold-rolled, and plates with prototypical CISCC. The effects of cold spray parameters on quality of cold spray coatings were investigated. Thickness, porosity, and phases in the as-deposited materials were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and correlated with microhardness and adhesion strength measured via micro-indentation and ASTM C633 pulling test, respectively. XRD analysis of the coatings was also conducted to examine the effects of cold spray condition on residual stress state in the coating. Detailed cross-sectional examination of coating/substrate interfaces was performed with transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS). Dense and continuous coatings with good adhesion strength, high hardness, and high degree of compressive stress were produced for the various substrate conditions by adjusting cold spray parameters. The results demonstrate that a cold sprayed stainless steel coating is a viable option to provide a physical barrier against CISCC in fusion weld regions of stainless steel in corrosive chloride salt-bearing environments.

Metallization of Fiber Reinforced Composite by Surface Functionalization and Cold Spray Deposition

The cold spray deposition process has gained interest as a promising technique for producing metallic coatings on polymers and composite materials thank to its low working temperatures. However, poor adhesion of metallic particles on polymeric substrates and the brittle nature of these materials lead to generation of cracks under the impact of the sprayed particles, limiting its application to polymeric matrix composite. The interposition of an intermediate metallic layer over the thermoset composite to be coated has been claimed to improve the adhesion of the sprayed particles and the formation of a stable link between the metal coating and the underlying polymer panel. The present work discusses a methodology that integrates the manufacturing of glass reinforced epoxy panels having functionalized surface and the subsequent production of a dense metallic layer by cold spray. Pure copper and titanium metallic powders, having spherical and irregular shape respectively, were placed on the top of the stack of dry glass fiber fabrics. Resin infusion process was then applied to impregnate the glass fabrics providing the simultaneous functionalization of the composite panel. In order to assess the effectiveness of the produced substrate, and of the proposed procedure, metallic coatings have been finally deposited on manufactured composite panels by means of a low-pressure cold spray facility. Regardless the spraying condition (namely gas temperature, stand-off distance, sprayed particles), copper samples showed a remarkable erosion of functionalized layer after cold spray process with pronounced damages of the composite substrate. On the other hand, effective depositions have been observed on titanium samples under specific combination of process parameters.

Particle deformation and microstructure evolution during cold spray of individual Al-Cu alloy powder particles

This paper examines the single particle impact process for a series of Al-Cu alloy powder particles with 2–5 wt% copper, performed using a low-pressure cold spray system with helium as the carrier gas. The cold spray deposition process is fundamentally controlled by the deformation processes, which occur during single particle impacts. Single particle depositions on steel substrates were produced for each composition over a range of gas temperatures (225–325 °C). Cross sections from single, impacted particles were produced using focused ion beam methods. The deformation microstructure in individual cold sprayed particles was studied using precession electron diffraction (PED) and transmission Kikuchi diffraction (TKD) techniques. For Al-Cu alloy particles, the amount of deformation estimated using a compression ratio did not show a significant difference with varying copper alloy additions. The single particles experienced large deformation upon impact, and ultrafine grains were formed at the particle/substrate interface via dynamic recrystallization. The particles were bonded to the steel substrate via a thin amorphous layer at the interface.

Improving deposition efficiency in cold spraying chromium coatings by powder annealing

Annealing of attrition-milled, electrolytically produced chromium powder has been investigated to improve cold spray coating deposition efficiency of pure chromium on Zr-alloy substrate for light water reactors with the goal of enhancing high-temperature oxidation resistance. The annealing heat treatment at 800 °C for 5 h induced microstructural transitions in the powder such as the development of equiaxed grains and strain relaxation, both associated with a measured decrease in nano-hardness. Deposition efficiency of the annealed powder was about three times more than the as-received electrolytic Cr powder. In addition, the utilization of the annealed powder reduced substrate deformation effects. A qualitative explanation of the effects powder microstructure on the cold spray deposition process in terms of the resulting coating microstructures and deposition efficiencies has been introduced. Finally, high-temperature exposure tests indicated that oxidation resistance of these Cr coatings was comparable to that previously reported for those produced using gas-atomized Cr powder. This study suggests that annealing of electrolytic Cr powder is a practical and economically favorable pathway to produce oxidation-resistant cold spray Cr coatings. More generally, use of the widely available electrolytic and mechanically milled powder vastly opens scope of cold spray deposition process, where atomized powders may not be either available or challenging to produce.

A comparison of cold spray technique to single particle micro-ballistic impacts for the deposition of polymer particles on polymer substrates

A laboratory-scale cold spray system with the capability of accelerating 10–100 μm polymer particles up to Mach 2 was used to deposit polystyrene and polyamide particles on a variety of different substrates for both cases of like-on-like deposition and deposition onto a melt-cast low-density polyethylene (LDPE) substrate. By systematically varying the particle temperature and impact velocity, the deposition window was developed for each particle and substrate combination in order to understand the cold spray processing conditions necessary to form coatings. The results were compared to those of the micro-ballistic single particle impact experiments. In the latter technique, an ablation laser pulse was used to accelerate a single polymer particle to over 400 m/s while being tracked during flight and rebound from the substrate using ultrafast laser photography. Single particle impact studies provide information about the particle impact dynamics including the plastic deformation of a successfully deposited particles and the coefficient of restitution of a rebounding particle that cannot be monitored during cold spray. Particles of both polyamide and polystyrene were found to deposit on a soft LDPE substrate at similar impact velocities using both deposition techniques. A number of differences between the two techniques were also observed. Like-on-like deposition was only found to be successful in cold spray. Additionally, when single particle impacts successfully deposited, the efficiency of deposition was close to 100%, while for the cold spray processes the deposition was <5%. These results suggest multiple particle impacts and/or surface roughness can play a major role in the effectiveness and efficiency of the cold spray deposition process for polymers.

Microstructure and mechanical properties of cold sprayed 6061 Al in As-sprayed and heat treated condition

Microstructural and mechanical properties of cold sprayed 6061 aluminum deposits on 6061-T6 aluminum alloy substrates are investigated under various heat treatment conditions, i.e. as-deposited, stress relieved and T6. The local mechanical property variation in the as-deposited material are explored using nanoindentation technique, and correlated with microstructural characterization conducted via electron back-scattered diffraction. It is found that the prior particle boundaries have ~0.4GPa higher hardness than particle interiors, which is attributed to grain refinement in these regions promoted by local dynamic recrystallization. Also, the bulk-scale mechanical properties of the deposits are evaluated by microtensile testing in various post-heat treatment conditions and compared to those of conventionally processed 6061-T6 aluminum. The as-deposited material showed markedly higher ultimate strength (~460MPa) and lower ductility (~3%) compared to conventionally processed material and this is attributed to significant cold working during the cold spray deposition process and associated grain boundary strengthening and dislocation strengthening mechanisms. Heat treated specimens showed a slight improvement in both ultimate strength and ductility compared to the as-deposited condition. These improvements are attributed to an improvement in metallurgical bonding at prior particle boundaries and a modest increase in the density of strengthening precipitates. Fractography of the specimens revealed that the heat treatment also changes the fracture characteristics of the cold sprayed 6061 aluminum deposit. The residual stress profiles and bond strength of the deposits are also studied using x-ray diffraction, tensile pull-off and three lug shear testing, respectively.

Simulation of the Cold Spray Particle Deposition Process

Cold spray is a rapidly developing coating technology for depositing materials in the solid state. In this work, the cold spray particle deposition process was simulated by modeling high-velocity impacts of spherical particles onto a flat substrate under various conditions. For the first time, we proposed the coupled Eulerian–Lagrangian (CEL) numerical approach as a means of solving the high-strain rate deformation problem. Using this approach, we observed a compressive stress region at the interface between the particles and the substrate induced by large plastic strains in the materials. Due to the high contact pressure (about 1 GPa) and the short contact time (about 40 ns), the high-strain rate (106 s-1) plastic deformation region was only a few micrometers deep and was localized mainly at the bottom of the particle and substrate surface. The ability of the CEL method to model the cold spray deposition process was assessed through a systematic parametric study including impact velocity, initial particle temperature, friction coefficient, and materials combination. The higher the impact velocity, the higher the initial kinetic energy, leading to more substantial plastic deformations and significant temperature increases in the substrate. The initial particle temperature has a greater influence on the equivalent plastic strain than on the temperature increase in the substrate. Friction has a limited effect on the temperature distribution and increase in the substrate, and the equivalent plastic strain increases only slightly as the friction coefficient rises. Four combinations of particle/substrate materials (Cu/Cu, Al/Al, Cu/Al, and Al/Cu) were considered in our study. Obviously, the particle's material had a greater influence on the deposition process and on the deformation than the substrate material. Concerning the particle's material, a higher-density material, such as Cu, has a higher initial kinetic energy, which has the advantage of increasing the contact area and contact time, resulting in better bonding between particles and substrate. Compared to other numerical methods (Lagrangian, arbitrary Lagrangian–Eulerian (ALE), and smooth particle hydrodynamics (SPH)), the CEL approach is globally more accurate and more robust in high-strain rate deformation regimes.

Development of CoNiCrAlY oxidation resistant hard coatings using high velocity oxy fuel and cold spray techniques

High velocity oxy fuel (HVOF) and cold spray techniques have been used to form oxidation resistant hard coatings for bond coat application for gas turbine blades. Though both techniques accelerate powder particles with high kinetic energy, the coatings formed differ considerably in their microstructures. In the former, high pressure is created by burning gases such as acetylene, propane or kerosene at high pressure and generating high temperature (3500 to 4500°C) in the gun. This gives high acceleration to powder particles which melt and deposit on substrate layer by layer with splat cool mechanism. On the other hand, large kinetic energy (KE) is generated in cold spray by passing carrier gases such as He or N2 through a converging–diverging nozzle, with a lower gun temperature of around 500°C. Here the particles are not liquid droplets because of lower temperature and the deposition mechanism is not a splat cooling, but a high impact of solid particles, which results in plastic deformation, making a very adherent coating.In this work, CoNiCrAlY powder was used. Presence of Al creates suitable deformation properties on impact. The powder was deposited on 316L SS substrate using HVOF and also by cold gas dynamic spray (CGDS) deposition process. In the latter, there are two processes, which give two different kinetic energies, depending upon the gas used, nitrogen or helium. The latter gives much higher KE. The deposited coatings were characterized and subjected to wear and oxidation studies. One of the interesting results was that the oxidation resistance of CGDS coating was much superior to that HVOF coated stainless steel with low wear rate and better friction behavior.

Mechanical Property Mapping of Cold Sprayed Ti Splats and Coatings

Profile nanoindentation and nanoindentation mapping were used to investigate the mechanical properties of commercially pure cold spray Ti splats and coatings deposited at increasing deposition velocities. Three regions in the cold spray Ti splats have been indentified: the impact region, the jetting region, and the upper splat region. The mechanical properties measured in these regions were tied to the cold spray deposition process with help of optical and scanning electron microscopes. The jetting region was observed to contribute to a metallurgical bonding of cold spray splats to cold spray splats and was measured to have low hardness in comparison to the splat impact site and similar to the hardness in the upper splat region. No increase in the profile coatings hardness with increase in the particle in-flight velocity and coating thickness was found. A correlation between the mechanical properties and the presently known deposition temperature, stress and dislocation density models was made.