Effects of α2 spacing on creep deformation characteristics of hard oriented PST crystals of TiAl alloy

Hard oriented PST crystals of a Ti-48 mol%Al alloy, in which lamellar boundaries are aligned parallel or perpendicular to stress axis, were creep tested. PST crystals of different α2 spacing were used: one has the equilibrium amount of α2 phase and the other contains an excess amount. Activation energy for creep rate of the former is 350 kJ/mol, being close to that of self-diffusion. The other crystal having fine α2 spacing provides lower creep rate due to its more significant strain hardening in the primary creep stage. This crystal shows substantially high activation energy of 510 kJ/mol. The superior creep resistance of the fine α2 spacing and its high activation energy is discussed in conjunction with the characteristics and degradation of lamellar structure in the material having the fine initial α2 spacing.