Bonding Characteristics of Cold Sprayed Copper Coating on Alumina Coated Q235 Steel Substrate

Cold spraying metallic coatings on ceramics (Ceramics Metallizing) are widely concerned in electrical industry due to its high density, low oxidation and high electrical conductivity. However, the bonding reliability of cold spraying coating on ceramics is usually considered to be poor since the metal particles don’t experience melting. The present paper is to exam the bonding quality of a cold spraying copper coating on a thermal sprayed alumina layer influenced by ceramics roughness and copper particle hardness. Pure copper coatings were successfully deposited on Al2O3 coated Q235 steel substrate with different roughness by cold spraying at 260 ℃ and 1.6 MPa using different hardness pure copper powders. The bonding quality and characteristics were studied by analyzing the surface, the cross-sectional microstructure of the coating and its interface after pull-off test. The results indicate that the high bonding quality (ranging from 8.26 MPa to 11.35 MPa) between copper coating and Al2O3 layer attributes to both metallurgical and interlock effect, which is mainly influenced by the hardness of the copper powders instead of Al2O3 surface roughness. The soft character of the pure copper powder makes it ready for deformation, subsequently interlocks with Al2O3, fills into the pores more completely, which increases the bonding quality between the copper coating and the Al2O3 layer

Study on the Growth of Holes in Cold Spraying via Numerical Simulation and Experimental Methods

Cold spraying is a promising method for rapid prototyping due to its high deposition efficiency and high-quality bonding characteristic. However, many researchers have noticed that holes cannot be replenished and will grow larger and larger once formed, which will significantly decrease the deposition efficiency. No work has yet been done on this problem. In this paper, a computational simulation method was used to investigate the origins of these holes and the reasons for their growth. A thick copper coating was deposited around the pre-drilled, micro-size holes using a cold spraying method on copper substrate to verify the simulation results. The results indicate that the deposition efficiency inside the hole decreases as the hole become deeper and narrower. The repellant force between the particles perpendicular to the impaction direction will lead to porosity if the particles are too close. There is a much lower flattening ratio for successive particles if they are too close at the same location, because the momentum energy contributes to the former particle’s deformation. There is a high probability that the above two phenomena, resulting from high powder-feeding rate, will form the original hole, which will grow larger and larger once it is formed. It is very important to control the powder feeding rate, but the upper limit is yet to be determined by further simulation and experimental investigation