Interrupted compression creep tests were performed at 973K and 350Mpa in order to study strain-dependent microstructural changes in near-γ equiaxed Ti-48Al-2Cr-2Nb-B alloy. The dislocation densities and volume fractions of deformation twins were measured within the range of strains where sharp creep-rate minima occurred. A steep decrease in the creep rate during an initial 1% of strain was associated with a considerable increase in the densities of ordinary dislocations and super-dislocations. Twinning processes were rather limited during this primary stage. In the strain range of minimum creep rate, the volume fraction of deformation twins grew due to the increasing number of twinned grains and the decreasing spacing between individual twins. On the basis of the results, it was suggested that in pure and near-TiAl equiaxed grain microstructures, an increase in the creep rate past the minimum - and its renewed gradual saturation - reflected the contribution of deformation twins to creep-strain accumulation kinetics. That is, deformation twins relaxed incompatibility stresses which built up during primary creep, and twinning supplied up to 30% of the overall strain in late stages of creep.

Dislocation Slip and Deformation Twinning Interplay during High-Temperature Deformation in γ-TiAl Base Intermetallics. A.Dlouhý, K.Kuchałová, J.Błezina: Materials Science and Engineering A, 2001, 319-321, 820-6