From the previous study related to Cu-Cr composites for thermal conductive materials accomplished via cold spray process,it was revealed that Cr surface quality and Cr particle size influence the deposition efficiency(DE)of Cu-Cr mixed feedstock powders.On the other hand,in some earlier studies,it has demonstrated that the Cu particle morphology influences the DE as well.In this study,the Cu-Cr composite coatings were fabricated using Cu-50mass%Cr mixed powders, and the influence of Cu particle morphology on the DE was investigated.The Cu-Cr mixed powders were prepared by using spherical and irregular Cu feedstock powders.The Cu-Cr coatings were fabricated onto OFC(Oxygen-Free Copper)substrate with N2 carrier gas.The irregular Cu particles adhered onto the substrate with remarkably flattened morphology,since the deformability of the irregular Cu powder was higher than that of the spherical Cu.By using the irregular Cu powder,the DE of the Cu-Cr mixed powder was improved more than 1.5 times compared with using the spherical Cu powder.However,the Cr content in the coatings was not increased.It was thought that the effect to prevent rebounding of the Cr particles by the irregular Cu particles is small,because of flattened and thinned Cu morphology on the Cr particles.In addition,it was considered that the local melting or softening did not occur in the irregular Cu particle/Cu substrate boundary,since the kinetic energy of the irregular Cu particle was absorbed in its remarkable deformation.Therefore,the irregular Cu particles were mechanically bonded on the substrate,and the adhesion strength of the coatings using irregular Cu powder was 1/10 or less compared with the case of using spherical Cu powder.After the heat treatment at 1093 K,the thermal conductivity of the coating using irregular Cu powder decreased by 2% as a result of the porosity increase of Cu matrix.
For long life-time durability of advanced gas turbines, protective coatings, which shield the underlying substrate superalloys from oxidation and corrosion attacks, are essential requirements for the hot section components. Conventionally, MCrAlY (where M indicates Co, Ni or their combinations) is deposited on the substrate as the protective coating, as well as the bond coat of thermal barrier coating system, by using low pressure plasma spray (LPPS) and high velocity oxygen fuel (HVOF) processes. Recently, Cold spray (CS) technique has been investigated as the coating process for those coating. These coatings induce additional thermal stress due to the mismatch of thermal expansion coefficient between the substrate and the coating, which impel the substrate to be exposed to more severe conditions. Thus, thermo-mechanical fatigue strength is one of critical issue to determine the life. In this work, the damage behaviors by thermo-mechanical fatigue loading were investigated in a CS protective coated Ni-base superalloy IN738LC. The high temperature fatigue strength of protective coatings was affected by the coating process due to the residual stress induced by coating process.