In this work, single component 316L and Fe coatings, as well as mixed 316L/Fe coatings with a dual powder feeder to obtain various feedstock compositions, were deposited to measure the deposition efficiency (DE). Individual particle impact tests were performed on single component and composite coatings to understand the particle impact behaviors during deposition. Bond ratio (BR) were determined for the impact tests to correlate with the DE. Results show that the 316L powder has a better DE than Fe, whereas the DE of the mixed 316L/Fe powders increases with increasing feedstock Fe content. The BR results correspond well with the DE of single component powders and mixed powders. The BR of 316L impacts onto composite coatings decreases with increasing Fe content, while the BR of Fe impacts plateaus at a high value regardless of composite coating composition, which leads to the increase of overall mixture DE.

Residual stress and adhesive/cohesive strength in cold-sprayed coatings are extremely important factors, and the balance between them can be a determining factor in coating failure, such as by delamination or cracking. Dominated residual stress to bonding stress should lead to coating peel off from its substrate. Up to now, it is still difficult to measure the residual stress of cold-sprayed coating especially inside it. In the present study, a high-energy X-rayed beam was utilized to penetrate the cold-sprayed coatings and the change of its diffraction angle can be detected. This gave a way to measure the residual strain inside the cold-sprayed coatings. With the scanning of the X-rayed beam and the detector at different locations, the strain of cold-sprayed coating at 2 directions can be obtained. Moreover, the residual stress of cold-sprayed coating can be calculated with the measured strain.

Tungsten carbide (WC) is a well-known material used to increase the wear resistance of iron-based composite materials that exhibit a favorable wettability with iron alloy particles. In this work, two different additive manufacturing technologies, i.e., cold-spray additive-manufacturing (CSAM) and selective laser melting (SLM), were used to fabricate WC/maraging steel 300 (WC/MS300) composites. An investigation comparing the microstructure and tribological behaviors of the composites was carried out. In addition, the evolution of the reinforcement phase during these two processes was characterized by SEM and EDS methods.

Cold gas dynamic spray is increasingly used for dimensional repair in the aerospace sector as it is capable of producing dense, oxide-free deposits of significant thickness and with good levels of adhesion and inherent mechanical strength. There is significant interest in extending the application of cold spray deposits to include structural, load-bearing repairs. However, particularly for high strength aluminium alloys, cold spray deposits can exhibit high levels of porosity and micro-cracks, leading to mechanical properties that are inadequate for most load bearing applications. In this work, heat treatment was investigated as a potential means of improving the properties of a cold sprayed Al alloy C355 deposit. C355 alloy deposits were produced using two process gas temperatures (350°C and 500°C) and three gas pressures (40, 50 and 60 bar) using a commercially available HPCS system. Microstructural analysis of the coatings revealed that the optimal microstructure (ca. 1% porosity) was obtained at 500°C and 60 bar. Therefore, coatings produced with process conditions of 500°C and 60 bar were heat treated at 175, 200, 225, 250°C for 4h in air and the evolution of the microstructure and microhardness was analysed. The results show that heat treatment at 225°C can decrease porosity (<0.2%) and retain high hardness (105 HV0.05 vs 130 HV0.05 as-sprayed). Further investigation was performed on as-sprayed and 225°C heat treated deposits. The results show that this heat treatment can halve residual stress (-50 MPa vs -100 MPa as-sprayed), and improve tensile properties (UTS). Therefore, this work has demonstrated that the heat treatment of C355 cold sprayed deposits at 225°C can significantly improve their properties.

In the current work, Ni-20Cr coatings have been developed for potential use in harsh environments of power plant boilers. A pre-synthesized Ni-20Cr nanocrystalline powder was deposited on T22 boiler steel using cold-spray process. The high temperature oxidation behavior of the coating was investigated under cyclic conditions at 900° C for 50 cycles, so as to understand the kinetics of oxidation. Moreover, high temperature erosion-corrosion (E-C) behaviour of the coating was ascertained under cyclic conditions in an actual boiler at 740 ± 10°C for 1500 hours. The oxidized and eroded-corroded samples were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses. The microhardness, oxidation and E-C data for the developed coating was compared with an earlier reported cold-spray Ni-20Cr coating, which was developed by using a commercially available micron-sized Ni-20Cr powder. The results showed that the developed coating was found to have 33% high microhardness in comparison with the microstructured Ni-20Cr coating. The oxidation and E-C rates of the steel were found to decrease significantly after the application of the developed coating by 89% and 68% respectively. Moreover the nanostructured coating outperformed the corresponding micro-structured Ni- 20Cr coating with regard to high temperature oxidation and E-C resistance to boiler steel by a significant fraction. The investigated coating was found to have oxidation protective oxides such as Cr 2 O 3 and NiO in its oxide scale and was found to be spallation-free.

In this study, cold sprayed Cu approximately 40 to 60 μm in thickness is deposited on 6063 and LD10 aluminum plate to improve wettability for low temperature soldering and to serve as a barrier layer to protect the substrate from gallium diffusion originating in the solder paste. The effect of the coating on wettability, diffusion, solder joint interface microstructure, and shear strength is investigated in detail.

This study investigates the effect of nozzle material on cold sprayed aluminum coatings produced using a downstream lateral injection system. It is shown through experimentation that nozzle material has a significant impact on deposition efficiency and particle velocity. It is proposed that the effects are related to complex interactions between particles and internal nozzle walls. The results obtained lead to the conclusion that nozzles with higher thermal diffusivity transfer more heat to particles when they make contact with internal surfaces, which increases deposition efficiency even though particle velocities are reduced.

The goal of this work is to establish a design for a cold spray nozzle that produces a flatter spray pattern. To that end, experiments and CFD calculations are carried out to investigate the influence of nozzle geometry and expansion ratio on the behavior of copper particles and gas flows during high-pressure cold spraying. It is found that there is an optimal ratio for the lengths of the diverging and parallel sections in a rectangular nozzle in regard to particle velocity and deposition efficiency. The results are also compared with circular nozzle designs.

In this study, cold sprayed Ni is deposited on Al substrates using different gas pressures. Spherical Ni powder was sprayed on cylindrical substrates using argon as the powder carrier and compressed air as the propellant. Coating and splat surfaces and cross-sections were examined, adhesion strength was measured, and particle velocity and temperature were determined through CFD simulations. The results show that denser, more well adhered coatings were obtained under higher propellant pressure. Higher gas pressure increases particle velocity, which intensifies material deformation and the disruption of surface oxides in the impact area, resulting in greater metallurgical bonding between the splats and the substrate. The formation of Ni-Al intermetallic phase at the interface region due to heat treatment was confirmed and its effect on bonding strength is discussed.

This study demonstrates a novel method for improving the corrosion resistance of cold sprayed Al6061 coatings. Large stainless steel particles were added to a commercial Al6061 powder and the mixture was deposited on Mg alloy AZ31B substrates using nitrogen gas at low working pressure and temperature. It is shown that the stainless steel particles had a shot-peening effect, thus increasing the density as well as the corrosion resistance of Al6061 coatings. SEM examination showed that no stainless steel particles were incorporated in the coating.

Interparticle bonding is considered the most important factor in cold sprayed coatings, determining mechanical properties as well as physical and chemical behaviors. In this study, a Cu feedstock with low oxygen content is deposited with relatively high spray pressure and temperature in order to improve interparticle bonding and obtain a coating cohesive strength. Mechanical bonding between deposited particles is deduced from fracture morphology and the deformation behavior of Cu particles is simulated by finite element analysis.

In this study, stainless steel powder is mixed with commercially pure iron and cold sprayed on steel in order to produce a metal composite with controlled properties. For these composites, porosity is very low, and annealing at 600-1100°C for an hour reduces it further. Annealing also sinters interparticle interfaces, leading to vastly improved fracture properties. Fully annealed single-component stainless steel exhibits a much higher strength than annealed CP iron, but adding just 20% stainless steel to iron produces a composite with the same fully annealed strength as that of stainless steel.

Four powder blends of Al and Ti were cold sprayed on Ti-Al-Nb substrates at 300°C. Test samples were heat treated in Ar at 500 °C then exposed to 950 °C air for 100-500 h. It was found that oxidation rates were significantly reduced by the coatings, especially those with lower Ti content. However, four-point bending tests revealed that the deposition of the protective layer reduced the flexural strength of the coated substrate. The results indicate that oxidation is not the only factor influencing the mechanical properties of intermetallics at high temperatures.

Thick Fe-Al deposits were produced by low-pressure cold spraying using heated air as the working gas. The coatings were isothermally annealed for two hours in Ar at temperatures from 250 °C to 750 °C. Changes in fracture behavior and microhardness were evaluated along with the microstructure and composition of newly formed phases. The results show that the evolution of intermetallic phases was driven by diffusion at temperatures above 550 °C. The new phases formed a hard skeleton that preserved the general shape of the samples during treatment despite the growth of external dimensions and porosity.

To improve the mechanical properties of aluminum coatings, ceramic reinforcement may be added resulting in an aluminum matrix composite. Two processing routes were investigated to manufacture aluminum matrix composite powders for thermal spraying: ball milling and mixing. Three sizes of SiC reinforcement particles were used: 2, 15, and 25 µm. For the ball-milled powders, morphology and microstructure were investigated as a function of SiC grain size and milling time. It is shown that the hardness of the composite and the efficiency of the spray process depend on the size of the hard particles as well as the preparation method. Friction tests were also carried out and the results are shown to correlate with coating microstructure.

In this study, cold spraying is used to develop WC-Co coatings with a WC-10Co core as reinforcement and a Co-rich WC-Co matrix as the binder. Core-shell structured powders were prepared by mechanical milling and coating samples were deposited by cold spraying. Post-spray annealing was carried out to further modify the coating microstructure. WC-Co coating microstructure and mechanical properties were investigated along with various structure-property relationships. It was found that a WC-Co layer with a porosity of only 0.7 % was realized by cold spraying the mechanically milled powder and that annealing at 900 °C for 2 h resulted in a remarkable improvement in fracture toughness with no evident change in hardness.

This study demonstrates the feasibility of an in-situ heat treatment for cold spray coatings. By controlling heat flow, temperature gradients are maintained in the coatings, leading to the development of graded mechanical properties. Initial experimental results validate both the starting idea and the first results of numerical simulations.

In the present study, spherical Ti-6Al-4V powders were cold sprayed on titanium, aluminum, and magnesium alloy substrates to investigate influences over a wide range of damping conditions and respective deceleration of impacting particles. Single impacts were produced via wipe tests and bonding was evaluated by cavitation testing followed by SEM examination of impact and fracture morphologies. The results show that better bonding is achieved for material combinations with similar properties due to high adiabatic shear instabilities that result in microfusion at the particle-substrate interface. In the case of dissimilar materials, the conditions for bonding can be reached in an intermediate stage, but bonded areas may later separate due to particle movement around the interface.

In this work, Al and Al-Al 2 O 3 coatings up to 8 mm thick were cold sprayed on AZ91D magnesium alloy substrates. Microstructure, microhardness, bond strength, and corrosion and wear resistance were studied to assess the viability of using these coatings to restore dimensionally degraded parts and protect them from further corrosion and wear.

This work evaluates a new cold-spray technique for coating the inner surface of pipes. Rather than rotate the pipe as in previous methods, a radial supersonic nozzle is translated along the pipe axis, leaving behind a continuous coating. In a demonstration, the new method is used to apply aluminum, copper, and nickel coatings inside steel and aluminum pipes with inner diameters of 45-100 mm.