The pseudoelasticity of a Ni45Ti50Cu5 alloy

Since several years the Ni(50-X)Ti50CuX alloys are attentively considered for the interesting features related to the B2-->B19' transformation involved in the pseudoelastic behavior. In contrast with the binary NiTi, where two martensitic transformations, B2-->R-phase and R-phase-->B19' can overlap, in the ternary alloy a single transformation is expected with a narrower hysteresis. The pseudoelastic behavior of a Ni45Ti50Cu5 is here thoroughly investigated both as a function of different thermal treatments and of the maximum applied strain. The minimum hysteresis width of the pseudoelastic cycle appears for a thermal treatment of 450 degrees C and decreases with stress cycling. The stress induced transformation involves, however, a single process whenever the maximum applied strain is smaller than the transformation strain. When the attained strain exceeds the transformation strain, another transformation sets in as supported by electrical resistance measurements performed concomitantly to stress-strain tests.