Oxidation behaviors of alloys containing β/B2 phases of Ti-45Al-Mo-Nb alloys and evaluation of the oxidation behaviors of Si pack cementation coated alloys

Alloys containing the β/B2 phases of Ti-45Al-3Mo, Ti-45Al-3Mo-2Nb and Ti-45Al-5Mo were prepared using an vacuum arc-melting machine. Heat-treatments were carried out at 1250 ^o C in an Ar atmosphere. The temperature of 1250 ^o C is the temperature region of phase α + γ + (β/B2), and the heat treatment condition which improves mechanical properties by decreasing the fraction of the β/B2 phase. The presence of the β/B2 phase can result in relatively weakness at high temperatures and collapses the lamellar structure of the α ₂ / γ phase during heat treatment. The transient oxidation behaviors of Ti-45Al-(3, 5)Mo-(2Nb) (at%) alloys were investigated in an ambient atmosphere at 900 and 1000 ^o C. Initial oxidation behaviors and oxidation resistance of the three alloys were compared at 1000 ^o C. The oxidation resistance of the Ti-45Al3Mo-2Nb alloy containing Mo and Nb was the most remarkable among the three alloys at 900 ^o C and 1000 °C. At the same time, Si pack cementation coated Ti-45Al-3Mo-2Nb alloys and oxidation behavior were also analyzed. The phase sequences of the multilayers of τ ₂ / Ti ₅ Si ₄ / TiAl ₃ / TiAl ₂ /TiAl were observed on the substrate. Also, a diffusion pathway of the silicide coating layers in the ternary phase diagram of Ti-Al-Si was proposed. The oxidation resistance of the silicide coated TiAl alloys was improved during the oxidation tests at 1000 ^o C.