Customization of residual stress induced in cold spray printing

It is generally believed that because of deposition at a temperature lower than the melting point, and high impact velocity of particles in cold spray printing, beneficial compressive residual stresses are induced in the substrate and coating. We have examined this general belief by identifying four major factors influencing the formation of residual stresses: coating and impact-induced temperatures, thermal mismatch of coat and substrate, heat transfer rate, and impact peening effect. A series of experiments is developed to allow studying these effects separately and to investigate their interactions. It is concluded that the heat input and heat transfer rate are the key controlling factors in the sign of the residual stress. Furthermore, we show that one can control the formation of residual stress to a desirable pattern, i.e., compressive in both the coating and the substrate near the interface. Using such parameters, two distinct residual stresses, tensile and compressive, were produced in the Al7075 coated AZ31B sheet. Further, the quality of the two coatings is measured through computerized tomography, surface roughness, and hardness measurements. It is shown that the density and hardness of the compressive samples are higher, while the roughness is lower than the tensile sample.

Automated summary

This study examines the formation mechanism of residual stresses in cold spray printing by investigating four major factors. It is found that heat input and heat transfer rate are key factors in controlling the sign of the residual stress. Experimental results show that desirable patterns of residual stress can be achieved by controlling parameters, leading to higher density and hardness, and lower roughness in compressive samples compared to tensile ones.