On the four-phase reactions in the Ti–Ni–Al system

Two four-phase reactions of transition type in the Ti–Ni–Al system were studied on several alloys, which were annealed at carefully set temperatures and quenched. The phase constitution was established by XRD and EPMA analyses. Due to sluggish reaction kinetics, the transition temperatures were defined by annealing and quenching techniques as no DTA signals could be received. For the reaction NiAl + TiNiAl ⇔ TiNiAl2 + TiNi2Al, the transition temperature was found to be 925 °C ± 15 °C and for the reaction TiNiAl + Ti3NiAl8 ⇔ TiAl2 + TiNiAl2, the transition temperature was found to be 990 °C ± 15 °C. Furthermore we confirmed the three-phase field TiNi2Al + Ti3Al + Laves phase (TiNiAl), as reported at 900 °C by Huneau et al. in 1999.