Effects of Strain-Rate and Cobalt Content on the Deformation and Failure of WC–xCo under Compression

Author(s):

Tusit Weerasooriya, Paul Moy, and Weinong Chen

Abstract:

The quasi-static, intermediate, and dynamic compressive responses of tungsten-carbide cermets alloyed with approximately 12 wt% and 6 wt% cobalt (Co) have been determined as a function of loading rates. To determine the dynamic properties, a modified split-Hopkinson pressure bar is used with wave shaping and a spherical joint. A similar spherical joint also is used in the quasi-static and intermediate rate experiments to minimize stress concentrations in the specimen through precise alignment loading. The compressive stress–strain response of the cermets is slightly nonlinear for both approximately 12 wt% and 6 wt% Co materials, and nonlinearity increases with the increase in Co content. Compressive strength increases with the strain rate for 12 wt% Co (from 4.5 GPa at quasi-static to 4.9 GPa at dynamic rates). Failure stress initially increases with strain rate for 6 wt% Co material (from 4.8 GPa at quasi-static to 5.1 GPa for intermediate [1/s] rates), but then decreases to 4.6 GPa at higher rates. The rate dependency of the failure stress is described by two models. In addition, carefully designed recovery experiments were executed to evaluate the evolution of microstructural damage during high-rate loading. Micrographs indicate that the crack propagation process is predominately intergranular.