Deformation behavior and microstructural evolution of Ti-6Al-4 V alloy under compression with confining pressure

Ti-6Al-4 V alloys have attracted increasing attention as candidates to meet targets for lightweight applications in the automotive, aerospace and other industries. To improve the plastic deformation capacity and mechanical properties of deformed parts, this paper proposes a forming process under superimposed hydrostatic pressure. Ti-6Al-4 V alloys were subjected to compression under liquid at a pressure of 175 MPa, which caused superimposed hydrostatic pressure during the compression process. This study revealed the deformation behavior and microstructural evolution of Ti-6Al-4 V alloys under such loading conditions for the first time through experimental, simulation and theoretical analyses. Multiscale characterization (SEM/XRD/TEM) reveals that hydrostatic pressure induces activation of {$10\overline{1}1$} and {$10\overline{1}2$} α-twins to accommodate deformation, the formation of coherent α/β interfaces and a nonrandom V distribution in the α phase. In comparison to the normal-pressure compression sample, the ultimate compressive strength, hardness, and compression ratio were only 1229.9 MPa, 294.1 HV, and 35%, respectively. The high-pressure compression sample exhibits a superior combination of strength, as evidenced by its ultimate compressive strength (2004.9 MPa), hardness (364.8 HV), and plasticity (42.5% compression ratio). The synergy is attributed to three coupled mechanisms under high pressure: twinning-induced plasticity, interface strengthening and short-range ordering strengthening. Furthermore, theoretical geometrical phase analysis and crystal plasticity simulations reveal that high pressure decreases the stress in the α phase. The resulting significant improvement in both tensile and compressive strains can lead to the formation of a high density of twins. Concurrently, it has been demonstrated to increase the resistance of the β phase to stress, thereby preventing the β phase cracking that is frequently observed in normal pressure compression. These results provide a promising pathway for overcoming the severe engineering challenges caused by the low room-temperature plasticity of Ti-6Al-4 V alloys.