Evidence for mechanical softening-hardening dual anomaly in transition metals from shock compressed vanadium

Abstract

Solid usually becomes harder and tougher under compression, and turns softer at elevated temperature. Recently, compression-induced softening and heating-induced hardening (CISHIH) dual anomaly was predicted in group VB elements such as vanadium. Here, the evidence for this counterintuitive phenomenon is reported. By using accurate high-temperature high-pressure sound velocities measured at Hugoniot states generated by shock-waves, together with first-principles calculations, we observe not only the prominent compression-induced sound velocity reduction, but also strong heating-induced sound velocity enhancement, in shocked vanadium. The former corresponds to the softening in shear modulus by compression, whereas the latter reflects the reverse hardening by heat. These experiments also unveil another anomaly in Young's modulus that wasn't reported before. Based on the experimental and theoretical data, we infer that vanadium might transition from BCC into two different rhombohedral (RH1 and RH2) phases at about 79GPa and 116GPa along the Hugoniot, respectively, which implies a dramatic difference in static and dynamic loading, as well as the significance of deviatoric stress and rate-relevant effects in high-pressure phase transition dynamics.

43 pages, 16 figures, with Supplementary Material

References in corpus (3)

• Elastic constants and volume changes associated with two high-pressure rhombohedral phase transformations in vanadium
• Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations
• First-principles investigation of elastic anomalies in niobium at high pressure and temperature

Cited by in corpus (3)

• Pressure-induced structural phase transition of vanadium: A revisit from the perspective of ensemble theory
• Modified Steinberg-Guinan elasticity model to describe softening-hardening dual anomaly in vanadium
• High-pressure melting and elastic behavior of vanadium and niobium based on ab initio and machine learning molecular dynamics