Nano crystalline high energy milled 5083 Al powder deposited using cold spray

Abstract

• NC non-cryomilled Al alloy powder produced by high-energy milling technique. • Nanocrystalline structure of the powder is retained after cold spraying. • No change in nanohardness between the powder and the cold sprayed layer. • Little evidence of dislocations within the nanograins of the cold sprayed layer. Electron microscopy and nanoindentation are used to investigate the relationship between microstructure and nanohardness of a non-cryomilled, nanocrystalline 5083 Al alloy powder before and after being deposited by cold spray. Microstructural investigations observed the presence of nano grains in the powder microstructure, ranging from 20 to 80 nm and with a typical grain size of 40–50 nm. It was also revealed that the nanocrystalline structure of the powder is retained after cold spraying. As a result, almost no change in nanohardness was indicated between the powder and the particles interior in the cold sprayed layer. However, hardness was substantially higher in some regions in the cold sprayed layer, which was attributed to the particle–particle interfaces or other areas with very small nano grain size. The presence of some un-joined particle remnant lines was also found in the deposition and explained through Critical Velocity Ratio (CVR) of powder particles. Although cold spray is a high deformation process, there is little evidence of dislocations within the nanograins of the cold sprayed layer. The latter observation is rationalized through intragranular dislocation slip and recovery mechanisms.