Effect of thermal cycling on martensitic transformation temperatures in Ti - Ni - Cu shape memory alloys

摘要

Changes in martensitic transformation temperatures during thermal cycling in Ti - Ni - Cu shape memory alloys have been investigated by means of electrical resistivity measurements, thermal cycling tests under constant load and transmission electron microscopy. During thermal cycling without applied stress, the B2->B19' transformation temperature M_s decreased, while the B2->B19 transformation start temperature M_s kept almost constant. During thermal cycling with applied stress, in solution treated Ti - 45Ni - 5Cu alloy, changes in M_s depended on the amount of applied stress. That is, M_s decreased when the applied stress was 39.2 MPa, while its value kept almost constant when a stress of 117.2 MPa was applied. It was also found that M4 increased during thermal cycling in the solution treated Ti - 35Ni - 15Cu and Ti - 30Ni - 20Cu alloys, irrespective of the amount of applied stress. All changes in Ms and M4 during thermal cycling with applied stress in Ti - Ni - Cu alloys were explained well by a combination of the thermal cycling effect and the structural refinement effect.