The cold gas-dynamic spray and characterization of microcrystalline and nanocrystalline copper alloys

Abstract

This thesis presents research on the cold gas-dynamic spray processa relatively new technology that may be utilized to create metal coatings in the solid state. While the thermodynamics and fluid mechanics of the cold gas-dynamic spray process are well understood, the effects of feedstock powder microstructure and composition on the deposition process remain largely unknown. In particular, this thesis aims to shed light on these effects as they pertain to common face-centered cubic metals and their alloysnotably copper and brass. Deposition efficiency, coating thickness per pass, hardness, porosity and compositional variance were all characterized as functions of spraying pressure, spraying temperature and feedstock particle composition in each of the materials. This thesis presents evidence that while brass can be deposited using cold gas-dynamic spray, the resulting material does not possess a dense, uniform microstructure. In fact, deposits made with Cu-90/10 wt.% Zn brass have more than 400% more porosity than standard copper coatings, possess extensive microstructural cracking and wide compositional variance from grain to grain.