Abstract
The mechanical behaviour of a Ti50Ni47Fe3 alloy, which exhibits a well-defined premartensitic transition and a subsequent martensitic transformation, was studied systematically using tensile tests over a wide temperature range covering M s to above T R. Two-stage yielding was observed in the temperature range between M f and a critical temperature, denoted by T X(T X > T R). The first stage was confirmed to be associated with the premartensitic R-phase (rhombohedral phase) transition, while the second stage was associated with the martensitic transformation. The temperature dependences of the critical stress and strain indicated that the first stage divides into two temperature regimes at about T R. In the lower-temperature regime the rearrangement of the R-phase was found to be responsible for the first stage, while in the higher regime the stress-induced transition of the R-phase was responsible for the first stage. As with alloys exhibiting a thermo-elastic martensitic transformation, similar mechanical effects associated with the R-phase transition have been found such as the shape memory effect, the two-way memory effect and transformation pseudo-elasticity. This is reasonable, considering that the R-phase transition is associated with a rhombohedral lattice distortion. Overall, the present results were found to be consistent with the recent theory of the premartensitic R-phase transition developed by Salamon, Meichle, Wayman, Hwang and Shapiro (1979).
