Disruption of oxide films during spark plasma sintering of micrometric-sized Al powders and its effect on microstructure and tensile properties of the consolidated Al

Abstract

We describe an investigation on spark plasma sintering (SPS) of micrometric-sized (1–10 μm) Al powders and the associated microstructures and tensile properties of the consolidated Al. Our results show the presence of disrupted nanoscale oxide particles at grain boundaries (GBs) and micrometric-sized grains and a combination of high strength and acceptable ductility in the Al SPS-ed above 580 °C. Our research was motivated by the fact that the mechanisms underlying the disruption of oxide films and the formation of a metallurgical bond between Al powders during SPS, and the effects of the disrupted nanoscale oxide particles on grain size and mechanical properties in the consolidated Al, hitherto remain poorly understood. By investigating the densification mechanisms underlying SPS of Al powders and microstructure of the consolidated Al, we suggest that the disruption of oxide films can be primarily attributed to the action of a spark discharge; correspondingly, the metallurgical bond between Al powders results from the fusion of molten Al in the vicinity of neighboring Al powder surfaces. Based on calculations using a previously developed model, grain growth was impeded as a result of negative net driving forces for GB migration and grain rotation due to the presence of the nanoscale oxide particles at GBs. On the basis of a Hall-Petch mechanism, the high strength was rationalized by the micrometric-sized grains and the enhanced Hall-Petch slope. Based on microstructure of the consolidated Al, the acceptable ductility was attributed to a minimization in stress concentration due to the nanometric sizes of the oxide particles and the presence of ductile grain interiors.