Multi-dimensional Effect of Heat Treatment on Microstructure and Property of Ti₆Al₄V Alloy Fabricated by Selective Electron Beam Melting

The as-built Ti₆Al₄V component was subjected to a heat treatment of solid solution at 1020 °C for 2 hours and followed by aging at 500 °C for 8 hours. The pores in different positions of Ti₆Al₄V components before and after heat treatment were analyzed by X-ray computed tomography (XRCT). The results show that the porosity in the center of the component decreased, while the porosity in the periphery increased, which eventually resulted in the overall porosity of the component decreasing from 0.232 to 0.147 pct after heat treatment. The changes of porosity in different positions are related to the differences in scanning strategy, cooling condition, and thermal stress. The optical microscope (OM) and X-ray diffraction (XRD) observations reveal that the columnar grains in as-built Ti₆Al₄V are transformed into equiaxed grains with an average grain size of 342.02 μm, the α phase thickness increases from 0.90 to 1.21 μm, and the content of β phase decreases from 12.3 to 5.5 pct after heat treatment. The density of the as-built component increases from 4.418 to 4.423 g cm⁻³ after heat treatment. The changes of micro-hardness in as-built and heat-treated samples are determined by specific microstructure and porosity.