EFFECT OF THERMOMECHANICAL TREATMENT ON SHAPE MEMORY CHARACTERISTICS IN A TI-40NI-10CU (AT PERCENT) ALLOY

The effect of thermo-mechanical treatment on the shape memory characteristics in a Ti-40Ni-10Cu (at%) alloy has been investigated by means of electrical resistivity measurement, differential scanning calorimetry, X-ray diffraction and the thermal cycling test under constant load. The following results are obtained. (1) The transformation occurs in two stages, i.e., B2 reversible B19 reversible B19', in both the thermo-mechanically treated and fully annealed conditions; (2) both the B2 --> B19 and B19 --> B19' transformation start temperatures, M(s)' and M(s), are increased by thermo-mechanical treatments; (3) the transformation hysteresis and maximum recoverable elongation associated with the B2 reversible B19 transformation is increased from 11 to 16 K and from 3.2 to 3.7%, respectively, by thermo-mechanical treatments; (4) the recoverable transformation elongation is obtained even under the applied stress of 162.8 MPa in the thermo-mechanically treated condition, while considerably large residual elongation starts to appear at about 90 MPa in the fully annealed condition.