An investigation into microstructure and mechanical properties of cold sprayed 7075 Al deposition

Abstract

Cold spray deposition is well known to produce a highly deformed microstructure with large strain gradients across the individual particles composing the deposited layer. This study investigates the relationship between the as-deposited cold spray microstructure and the resulting local and coating-scale mechanical properties of 7075 aluminum powder deposited onto wrought 7075 aluminum substrates via high pressure cold spray. Local mechanical property variations were probed using nanoindentation and correlated with microstructural characterization conducted via various microscopy techniques. 7075 Aluminum powder particles experienced high deformation rates during impact, resulting in local microstructural variations, specifically grain size and dislocation densities, between particle interfaces and their interiors. Consequently, an average 0.5 GPa increase in nanohardness was observed in particle interface regions. This increase in hardness was concluded to be primarily the result of grain refinement promoted by local dynamic recrystallization, rather than from an increase in local dislocation density causing strain hardening behavior. Examination of the coating revealed a decrease in hardness and an increase in local grain size with increasing distance from the substrate. The effects of these microstructural variations on the quality of the deposition were also evaluated by tensile pull-off and three lug shear testing.