Brittle-to-ductile transition temperature and its strain rate sensitivity in a two-phase titanium aluminide with near lamellar microstructure

The temperature dependence of tensile properties of a two-phase titanium al uminide with nearly lamellar microstructure has been investigated and britt le-to-ductile transition (BDT) temperatures (T-BDS) have been determined un der different strain rates from 10(-5) to 10(-1) s(-1). It is found that T- BD rises with the increase of strain rate. From the positive strain rate se nsitivity of T-BD, the apparent activation energy of BDT is determined to b e 324 kJ/mol by means of Zener-Hollomon factor. The determined activation e nergy approximates to the activation energies of self-diffusion of Ti atoms , and inter-diffusion of Ti and Al atoms in TiAl phase. The approximation, fractography analysis and theoretical calculation using the Nabarro Model a dd up to the speculation that the BDT of the alloy is controlled by disloca tion climbing. (C) 1999 Kluwer Academic Publishers.