Ti-Al-Ni-Cu-Si alloy exhibiting low flow stress, high ductility at high temperature and high strengthening at room temperature

The microstructure and mechanical properties of Ti-Al-Ni-Cu-Si alloys were evaluated, and the effects of the addition of Ni, Cu, and Si were investigated. Microstructural analysis revealed that the alloy consists of two phases: the α phase and the eutectoid phase, with the precipitation of Ti2 (Ni, Cu) as an intermetallic compound (which is identified by SEM and TEM analyses). Tensile tests tested at various temperatures ranging from room temperature to 700°C showed that the Ti-Al-Ni-Cu-Si alloys such as Ti-3Al-0.5Ni-0.5Cu and Ti-3Al-0.5Ni-0.5Cu-0.3Si alloys (in mass%) exhibit a higher strength at room and intermediate temperatures (～500°C), and a lower stress at high temperatures ( ≥ 600°C) compared to conventional Ti-Al-V alloys having similar β phase stability. The results obtained in this study successfully suggest a new type of V-free Ti alloy with high strength from room temperature to 500°C and improved hot working ability (a low flow stress and a high elongation).