Deformation mechanism of WC single crystals under nanoindentation: Effects of surface defects and orientation on pop-in and hysteresis

TL;DR

This study investigates how surface defects and crystal orientation influence deformation mechanisms, pop-in events, and hysteresis during nanoindentation of tungsten carbide single crystals, revealing the role of dislocation activity and surface preparation.

Contribution

It provides new insights into the effects of surface defect density and crystallographic orientation on deformation behavior and pop-in phenomena in WC single crystals during nanoindentation.

Findings

Dislocation density affects elastic-plastic transition thresholds.

Dislocation motion causes staircase deformation and slip bands.

Pop-in events are linked to dislocation nucleation at shear strength.

Abstract

Nanoindentation was carried out on pure tungsten carbide (WC) on the basal (0001) and prismatic (1010) planes, using Berkovich and spherical indenters, in both single load and multi-load testing. The work focuses on correlating the load-displacement curves, including elastic to plastic deformation, size effect and hysteresis with the deformation behaviour of WC. With different specimen preparation processes, the elastic to plastic deformation started at different threshold loads: This observation was found to be due to the variation in surface dislocation density. Staircase deformation was observed thought to be caused by dislocation motion and the formation of slip bands; sudden displacement discontinuities in the load-displacement response - associated with dislocation loop nucleation - occurred at, or near the theoretical shear strength. Furthermore, discontinuities in load-displacement curves were also used to confirm that hysteresis loops were a result of plastic deformation, as they when the loading was purely elastic.