Phase transition and hardness evolution of a Ti-5Al-5Mo-1Fe-1Cr alloy subjected to isothermal aging.

In this paper, a Ti-5Al-5Mo-1Fe-1Cr alloy was isothermally aged at 500 °C for different periods. Phase transformation took place during the aging treatment. The phase transformation was studied by X-ray diffraction spectroscopy and transmission electron microscopy. The as-quenched sample was composed of matrix β (body-centered cubic structure) phase, ωath (hexagonal structure) phase and minor α (hexagonal close-packed structure) phase. The results showed that aging treatment promoted the β → ω → α phase transformations in the as-quenched alloys. Different isothermal aging time affected the contents and morphologies of the three phases inside the alloy and thus the hardness. It was found that the content of hard ω phase plays an important role in the hardness of the Ti-5Al-5Mo-1Fe-1Cr alloy. The hardness of alloy showed an overall decreasing trend as the aging time increased to 2 h, except for the temporary slight increase of the hardness at an aging time of 1 h.