β-Ti(M) solid solution formation and its thermal stability in a NiAl–Cr(Mo)–(Hf,Ti) near eutectic alloy

The effects of combined additions of Ti and Hf to NiAl–Cr(Mo) eutectics on the as-cast microstructure and its thermal stability are investigated through SEM, EDS and TEM, with focus on the formation mechanism of β-Ti(M, M = Hf,Cr,Ni) solid solution phase and its thermal stability after short-term heat treatment. The results show that, due to the presence of large concentrations of β-phase forming and stabilizing elements dissolved into the Ti solid solution phase during solidification, the thermodynamically metastable β-phase was preserved at room temperature. With respect to its thermal stability, within the experimental range examined, the β-Ti(M) solid solution phase, is not influenced. From the practical application point of view, this β-Ti(M) solid solution phase may offer application as a strengthening phase for the design of NiAl–Cr(Mo)–Hf based alloys.