Cold spray deposition and microstructure characterization of CuNi, CuSn, and CuNiSiCr coatings

Cold spray is a coating deposition technique that enables to produce a large variety of metallic coatings using supersonic powder particles. Pure copper (Cu) has been used as a model material for cold spray due to its high deposition rate. Nevertheless, many Cu alloys that are broadly used in engineering applications, including Cu10wt%Ni (CuNi), Cu-10wt%Sn (CuSn) and Cu-7wt%Ni-2wt%Si-0.9wt%Cr (MoldMAX V (R) High Strength Cu), have not been fully investigated in the cold spray process. Thus, there is still a lack of understanding of their deposition process, microstructure evolution and mechanical properties in these Cu-alloy coatings made by cold spray. In this study, we study the deposition efficiencies, porosities, microstructures and hardness of the cold sprayed Cu alloys and elucidate their deformation mechanisms. Our results show that all the coatings have high densities above 99 % and deposition efficiencies ranging from 73 % (CuSn), 80 % (CuNi) to 99.9 % (HS Cu). The average Vickers hardness of the CuNi, CuSn, and HS Cu coating samples are about 130 HV, 160 HV, and 190 HV, respectively, with HS Cu showing the highest work hardening rate. We find that these Cu coatings, particularly CuNi, exhibit heterogeneous microstructures with relatively large grains in the particle interiors and fine grains at the particle-particle interfaces, which are due to serve plastic deformation at the interfacial regions. Nanoindentation maps also show that the local nanohardness distributions are correlated to the heterogeneous microstructure observed.