Void formation driven by plastic strain partitioning during creep deformation of WC-Co

Abstract

Creep deformation of WC-Co composites at high temperature and stress is accommodated by either bulk WC creep or by Co-infiltrated grain boundary sliding. It has been proposed that certain grain boundaries are more susceptible than others to such sliding, and depending on the applied stress, the overall deformation rate can be limited by either mechanism. Here, we have used Electron Back-Scatter Diffraction to study the strain partitioning in each phase, the evolution in phase boundary and grain boundary misorientation, and void formation. Several WC-Co samples (Co contents ranging 7–13 % and grain sizes 0.5–1 μm) were deformed by unconstrained compression at 1000 °C under constant load in the range 0.5–1 GPa. The localised deformation state – as characterised by increases in pixel misorientation and inverse pole figure dispersion – increased significantly between 0.5 and 0.75 GPa for both phases, which may be associated with the onset of grain boundary sliding. The onset of the formation of creep voids occurred when the stress level was 0.75 GPa or more. Deformation was correlated with an increase in 60° Co_FCC /Co_FCC boundaries, and in 56° WC/Co_FCC boundaries. Boundaries with the latter misorientation angle may preferentially enable the Co infiltration process.