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, 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.

Alumina splats were deposited on the polished single crystal alumina substrates with two different crystalline facet orientations of [001] and [110] by atmospheric plasma spraying (APS) at a substrate preheating temperature of 900°C to examine the epitaxy during splat cooling. The cross-sectional samples for high resolution transmission electron microscopy examination was prepared by focused ion beam assisted scanning electron microscopy (FIB-SEM). The results show that the whole splats with a thickness ranging from ~600 to ~1000nm exhibited the same crystalline structure as the substrate. Moreover, the splat deposited on the single crystalline alumina substrates exhibited exactly the same orientation as the substrate. The results evidently indicate that the epitaxial grain growth occurs after alumina droplets impact on single crystal alumina substrate. The present results suggest that the crystalline structure of alumina deposit formed by plasma spraying can be possibly controlled by the substrate preheating temperature.

cBN/NiCrAl nanocomposite coating was deposited by cold spraying using mechanically alloyed composite powders. To examine the thermal stability of coating microstructure, the nanocomposite coating was annealed at different temperatures from 750 to 1000°C. The microstructure of composite coatings was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the nanostructure was retained in the coating when the annealing temperature was lower than 825°C which is 0.7 times of the melting point of NiCrAl matrix. The dislocation density significantly reduced when annealing temperature was higher than 750°C. The cBN particle growth became significant when the annealing temperature was higher than 825°C. The effects of crystal grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as the function of annealing temperature. The effect of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.

C-BNp/NiCrAl composite coating was deposited by cold spraying using a mechanically alloyed composite powder. To modify coating microstructure, especially the bonding at the interfaces between c-BN particles and NiCrAl alloy matrix, and bonding at the sprayed particle/particle interface, annealing treatment at series of temperatures in Ar atmosphere was carried out. The results show that a zigzag interface layer is formed at the interface between c-BN particle and NiCrAl matrix after annealing at 825°C for 300 min through reaction of c-BN with NiCrAl. It is also observed that the thickness of the interface reaction layer increases with the increasing annealing temperature. Moreover, the interface between spray particles and the plastic deformation ability of the cermet coating can be improved through post-spray annealing. Vickers microhardness test shows that the hardness decreases with increasing annealing temperature due to the reduction of work hardening effect and grain growth of NiCrAl alloy matrix resulting from recovery and recrystallization during annealing treatment.