High-pressure Elasticity of Novel (vnbtati)c High-Entropy Carbides

Acoustic velocities and elasticity of high P-T synthesized new (VNbTaTi)C high-entropy carbides (HECs) are reported at high pressure using large volume press (LVP)-based ultrasonic interferometry technique. Using the finite-strain equation approach, the bulk modulus and shear rigidity, and their pressure dependences, are derived from the current experimental data, yielding B0 = 261.6(2) GPa, G0 = 191.4(3) GPa, ∂B/∂P = 4.34(18), and ∂G/∂P = 1.83(6). Interestingly, the (VNbTaTi)C HECs is more incompressible than the superhard γ-B (~213.9GPa), and almost as incompressible as superhard PcBN (~254GPa). Meanwhile, its shear rigidity (~191.4GPa) is comparable to the superhard B6O-B4C composite (G = 202GPa), and as stiff as the (TiZrNbTa)C (193 ~ 195GPa) HECs. More strikingly, the fracture toughness is enhanced up to ~4.6(3) MPa·m1/2, and the Vickers hardness of (VNbTaTi)C HECs is ~22.6(2) GPa, which are significantly stronger than other high-entropy carbides. These new findings and results may be very important for its applications in extreme environments.