Shock compression of cemented tungsten carbides to 100 GPa: Structure of shock waves, Hugoniot relations, and strength

Abstract

Plate impact experiments are conducted on cemented tungsten carbides (WC) with a 3.7 and 6.0 wt. % cobalt binder to better understand their dynamic, high-pressure response to 100 GPa. The measured wave profiles show propagation of steady structured waves. Standard impedance matching procedures are used to determine the Hugoniot relations in the shock velocity-particle velocity ( U s − v p ) and Hugoniot stress-specific volume ( P − V / V o ) planes. The Hugoniot elastic limit of the samples is controlled by ductility of the Co binder and is determined to be 4.45 ± 0.29 GPa for cemented WC with 3.7 wt. % cobalt and 3.72 ± 0.24 GPa for a 6.0 wt. % cobalt binder. Both grades show a non-linear U s - v p relationship depending on whether the particle velocity is in the strength dominated or hydrodynamic regime. In the strength dominated regime, a non-linear decrease in U s is observed as v p increases from ambient to the material’s hydrodynamic limit. In the hydrodynamic regime, the U s - v p Hugoniot is linear and is determined to be U s = 4.97 ( ± 0.006 ) + 1.446 ( ± 0.018 ) v p km/s for WC with 3.7 wt. % Co and U s = 4.93 ( ± 0.006 ) + 1.463 ( ± 0.017 ) v p km/s for 6 wt. % Co. Both WC grades indicate shear-stress hardening with mean stress immediately after yield, followed by pressure softening, and then a sharp fall in stress carrying capacity as the mean stress is increased to ≈ 70 GPa (hydrodynamic limit) and beyond. This behavior is in contrast to pure WC ceramics, which show continued shear-stress hardening with mean stress to ≈ 80 GPa.