Shape memory behavior associated with a two-stage R-phase transformation in Ti-50.9at%Ni alloy

Abstract
It was first found by the present authors that a two-stage R phase transformation appears in a Ti-50.9at%Ni alloy aged at 473K. The two-stage R phase transformation is characterized by two DSC peaks prior to the martensitic transformation during cooling (the first R phase transformation on cooling is denoted by R ₁ and the second by R ₂). Transformation temperatures of both the R-phases, R ₁ and R ₂, increase with increasing aging time. According to thermal cycling tests under various constant stresses, transformation strain of R ₂ is larger than that of R ₁, With increasing applied constant stress, the latter strain increases and the former one decreases. However, total strain of both R ₁ and R ₂ is almost constant irrespective of stress.