Microstructural characterization and creep behaviour of as-cast titanium aluminide Ti–48Al–2V

Abstract

Solidification paths were established in a two-phase (α 2+γ) alloy of nominal composition Ti–48Al–2V (at.%). The alloy buttons were prepared by vacuum arc melting. The phases present in the alloy were characterized by X-ray diffraction, optical microscopy and scanning electron microscopy. Room temperature microstructure of the alloy consisted of colonies of (α 2+γ) lath dendrites and interdendritic γ segregate. The (α 2+γ) lath colony size was determined to be about 76 μm. Based on the dendritic morphologies and the orientation of the (α 2/γ) lath striations observed in the shrinkage cavities, it was established that primary β solidification occurs in the alloy. Creep behavior of the alloy in the as-cast condition was studied by employing the impression creep technique in the temperature range of 1033–1098 K and in the stress range of 187–420 MPa. The alloy exhibited power law creep in this regime. The stress dependence of the steady-state creep rate showed a stress exponent value of 4.0–4.6 and the activation energy for creep was found to be in the range of 320–340 kJ mol −1. This value is slightly higher than that for diffusion of Ti in single phase γ (TiAl). These results suggest the operation of a diffusion-controlled creep mechanism in the alloy. Microstructure of the deformed region under the indenter revealed formation of fine-scale lamellae and randomly oriented grains as a result of creep. The creep parameters obtained in the present study are compared with those in the literature on lamellar (α 2/γ) alloys.