Thermomechanical properties of cold-sprayed copper coatings from differently fabricated powders

Abstract

Cold spraying is a material coating deposition process that accelerates powders to high velocities, thereby causing them to undergo intensive plastic deformation upon impact in solid states at temperatures far below their melting point. The critical powder velocity is the most influential factor determining the bonding strength of cold spray coatings and strongly depends on the thermomechanical interactions between the sprayed powder and the substrate material. In this study, three commercially available Cu feedstocks fabricated through electrolysis (EP), gas-assisted water atomization (WA), and inert gas atomization (GA) were characterized and used to produce cold spray coatings. The kernel average misorientation (KAM) data from electron backscatter diffraction (EBSD) analysis were used to determine the plastic strain distribution of the Cu powders and coatings through local crystallographic misorientation. The percentages of the local misorientation within grains with angles higher than 1.5° in the EP (3.0%) and GA (2.8%) powders were similar, whereas that in the WA powder (0.6%) was the smallest. According to the EBSD data, more dynamic recrystallization and, in turn, more plastic strain release occurred in the as-sprayed EP and GA coatings than in the WA coating. The tendency of recrystallization of the twin grains in the as-sprayed GA coating and its influence on the ductility of the coating are discussed in relation to the GA powder's bonding mechanisms. The static recrystallization in the postannealing treatment (at 190 °C for 1 h) of the EP and GA coatings being more prominent than in that of the WA coating supports differences in dynamic recrystallization among the cold-sprayed coatings determined through EBSD analysis. The thermal conductivity of cold-sprayed Cu coatings is influenced by recrystallization and strain release.