Cryogenic Processing of Biomaterials for Improved Surface Integrity and Product Sustainability

Abstract

Improved functional performance and longer service life of biomedical products offer great sustainability benefits. Surface integrity, which can be modified by severe plastic deformation (SPD) processes, affects the functional performance of materials. Two SPD processes – burnishing and machining – were studied under cryogenic conditions. Cryogenic burnishing of a Co-Cr-Mo biomedical alloy using a novel burnishing tool led to significant grain refinement and 80% greater surface microhardness relative to the bulk. Cryogenic burnishing of AZ31 Mg alloy led to a more than 2 mm thick SPD surface layer with remarkably refined microstructure (grains <300 nm), where hardness was increased 95%. The SPD layer formed on AZ31 Mg alloy after cryogenic machining was about 60% harder than the bulk material. Furthermore, this layer enhanced corrosion resistance during incubation in simulated body fluid. The present results demonstrate significant surface and subsurface property improvement due to cryogenic processes of both alloys, thus providing improved sustainability.