The influence of high-pressure environment on the anisotropy in titanium alloy components fabricated by wire arc additive manufacturing

In this study, Ti64 titanium alloy samples were fabricated under environmental pressures of 0.1 MPa (ambient pressure) and 0.4 MPa (high pressure) using a self-developed high-voltage arc wire additive manufacturing system. The effects of pressure on the microstructural evolution and anisotropy of a titanium alloy were comparatively investigated using characterization techniques such as SEM, EBSD, and TEM. The results indicate that differences in the thermal history dominated by the deposition path lead to significant anisotropy in the Ti64 samples (XY plane > XZ plane > YZ plane). Under high pressure, the altered molten pool morphology and expanded remelting zone prolong the residence time in the medium-to-low temperature range, thus reducing the β-phase fraction in all directions to a lower level and thereby weakening the anisotropy. In terms of grain growth, β-phase grains tend to grow preferentially along the deposition direction (Z-direction) under ambient pressure. In a high-pressure environment, the synergistic effect of pressure and thermal deformation induced by the horizontal extension of the molten pool enhances the growth of β-phase grains within the horizontal plane and suppresses preferential orientation. At the microscopic level, thermal deformation promotes twin formation and leads to dislocation concentration at primary β-phase grain boundaries, consequently influencing the mechanical properties of the Ti64 samples.