Nanomechanical response of tungsten carbide single crystals in extreme conditions: Temperature and strain rate dependence

Abstract

The mechanical response of tungsten carbide (WC) single crystals under extreme conditions was investigated by means of pendulum-based nano-impact testing, from ambient to high temperatures. Dynamic hardness measurements and damage accumulation observations were conducted by single and multiple impact tests, respectively, at high strain rates (∼ 103-104 s-1). Large WC single crystals with different orientations, namely, (0001) basal and (101¯0) prismatic crystals, were studied. The results obtained from impact testing were compared to results acquired by high temperature nanoindentation in the quasi-static regime (10−2 s−1), at a similar length scale, up to 600 °C. Whilst basal WC crystals were shown to exhibit a higher dynamic hardness at high strain rates across the entire range of temperatures, the hardness of prismatic WC crystals at high strain rates were only found higher at temperatures below 200 °C and comparable at elevated temperatures. Post-mortem topographical scans revealed the generation of substantial plastic deformation during impact and large pile up formation in the vicinity of the impact imprints in prismatic crystals. Electron Channelling Contrast Imaging (ECCI) of the repetitive impacts suggested preferential planes for the accommodation of stress through plastic flow at high strain rates, as previously reported in the quasi-static regime. The results shed light on the mechanical behaviour of WC in extreme conditions, evidencing anisotropic mechanical behaviours.