Hierarchical microstructure induced by hydrostatic pressure in a metastable β-Ti alloy

Hydrostatic pressure is a crucial tool to regulate the structure and properties of materials. However, the influence of hydrostatic pressure on the microstructure of metastable β-Ti alloys remains unclear. In this work, the microstructure and hardness evolution of a metastable β-type Ti-30Zr-10Nb alloy under hydrostatic pressure (≤10 GPa) were investigated and compared with those under uniaxial pressure (≤1106 MPa). The results revealed that under hydrostatic pressure, Ti-30Zr-10Nb alloy formed a peculiar hierarchical microstructure composed of submicron-scaled α" plates with self-accommodating morphologies, nanoscale ω particles, and microscale shear bands containing nanoscale α" domains. The formation of a hierarchical microstructure effectively coordinates not only the isotropic macroscopic strains but also the local shear stresses under hydrostatic pressure. Compared to uniaxial pressure, the hydrostatic pressure facilitates the β to ω transformation, but hinders the β to α" transformation. The hardness of the Ti3010 alloy reaches approximately 319 HV at a hydrostatic pressure of 10 GPa, which is 28 % higher than the highest hardness obtained under uniaxial pressure. The current results highlight the promising potential of hydrostatic pressure in optimizing the mechanical properties of metastable β-Ti alloys.