From the previous study related to Cu-Cr composites for thermal conductive materials accomplished via cold spray process,it was revealed that the degree of Cr particle surface oxidation might affect their deposition efficiency.In this study,the Cu-Cr composite coatings were fabricated using mixed Cu and Cr powders with ratio of 50 mass% Cr onto OFC substrate with N2 carrier gas,and the effect of particle surface oxidation was examined by using oxidized Cr powders.The Cr content in the coatings was decreased with increasing of the thickness of Cr particle surface oxide,owing to decreasing of the deposition efficiency of Cr powder.It could be seen that the Cr surface oxide film remained during impact,and it was considered the decreasing of the Cr content was due to existing of the oxide film and its higher hardness.Furthermore,in the case of thicker oxide film,brittle fractures and cracks were observed at the individual Cr particles on the Cu substrate.It was assumed that these cracking and fracturing were started from brittle oxide film,and it might be one of the factors of deposition efficiency decrease. Therefore, it was expected that control of the Cr particle surface oxidation might be effective means for the improvement of adhesion and deposition efficiency of the Cu-Cr mixed powders.
Ni-based alloy coatings for anti-corrosion were prepared by cold spray process. Their microstructures, adhesionmechanism of the coatings, and influence of post heat treatment on the mechanical properties of the coatings were evaluated. The Ni-based alloy coatings were fabricated using Inconel-625 powder with the size range of 11-45 μm onto two different hardness mild steel substrates. Several micrometers pores were observed in the cross-sections of the coatings. The pores showed the tendency that became larger when the substrate hardness was low. In case of the substrate hardness of 336 HV, gaps existed at boundaries between the individual sprayed particles and the substrate, and it could be inferred that the as-sprayed coatings mechanically adhered with the substrate. In case of the substrate hardness of 198 HV, the individual sprayed particles metallurgically adhered with the substrate, and it could be seen that the adhesion mechanism of the coating was both metallurgical and mechanical. Since the metallurgical bonding at the boundary was promoted, the heat treatment improves the adhesion strength of the coatings. The adhesion strength of the heat-treated coatings are to more than twice that of as-sprayed coatings.