Elasticity, mechanical and thermal properties of polycrystalline hafnium carbide and tantalum carbide at high pressure

Hafnium carbide (HfC) and tantalum carbide (TaC), as potential ultra-high temperature ceramics (UHTCs), have attracted widespread attention due to their unique physical and chemical properties. Here, dense HfC and TaC ceramics are synthesized under high pressure and high temperature 15 GPa and 1700 °C, respectively. The sound velocities and elasticity behavior of sintered HfC and TaC under high pressure have been experimentally investigated by using ultrasonic interferometry and validated by first-principles study. The bulk and shear moduli with their pressure dependence have been determined as B0 = 272.6(2.7) GPa, G0 = 215.8(2.2) GPa, ∂B/∂P=3.44(5), and ∂G/∂P=1.74(3) for HfC, B0 = 355.9(3.6) GPa, G0 = 236.6(2.4) GPa, ∂B/∂P=3.98(5), and ∂G/∂P=1.65(2) for TaC. The Vickers hardness and fracture toughness of HfC and TaC are generated from empirical models. The present work provides deep insights into the engineering application of UHTCs HfC and TaC under high-pressure extreme conditions.