High-temperature deformation behavior of the gamma alloy Ti-48Al-2Cr-2Nb

The hot-workability of a two-phase (gamma + alpha-2) alloy, Ti-48Al-2Cr-2Nb, has been studied by conducting isothermal compression tests to 0.8 true strain over the temperature range of 975-1200 C at strain rates between 0.1 and 0.003/S. A deformation map showing temperature, strain rate, soundness of deformation, and isostress contours was constructed. Good workability is found from the low temperature/low strain rate regime to combinations of high temperature and either high or low strain rate. The upper-limit flow stress for good workability is between 450 and 500 MPa. Deformation induced softening occurs at all conditions. SEM and TEM examinations of the deformed specimens reveal that nonuniform deformation takes place at all strain rates, but cracking occurs mostly at high strain rates (e.g. 0.1/s), especially combined with low temperatures. The cracking appears to progress primarily along gamma/alpha-2 interfaces. It is thought that nonuniform deformation develops channels of shear bands, which in turn promote localized recrystallization, thus accommodating higher strains. 9 refs