In this paper, the authors report the interesting stress-strain results and an aging behavior found in single crystals of In-21, 22, 23, 24, 25 and 26 at. % Tl alloys. The stress-strain curves can be classified into three groups according to their shapes. In a high temperature region above martensitic temperature, Mₛ, while at a considerably low temperature region, superelastic loops are obtained. While at an intermediate temperature below Mₛ, the residual strain remains after removal of the applied stress, and this strain returns to zero when the specimen is heated up to above the reverse transformation temperature. That is the so-called shape memory effect. The twin boundaries migrated by the external stress were stabilized by strain aging under stress, and the activation energy for the aging process was found to be O.51±O.O3eV. The strain rate dependence of pseudo-elastic behavior is observed in the martensite phase and is explained by the dynamic aging between the moving twin boundaries and Tlatoms
