HYSTERESIS LOOPS IN STRESS-INDUCED BETA-18R MARTENSITE-TRANSFORMATION IN CU-ZN-AL

A detailed study of the characteristics of the hysteresis loops in stress induced transformations was carried out using a high resolution apparatus. Samples with two different thermal treatments, air cooled and water quenched from 1070 K, were tested. The contribution of the nucleation processes to the hysteretic behaviour was evaluated. It was found that the intrinsic pseudoelasticity, due to the interaction of the martensite with the dislocations, plays a crucial role in the phenomenology of the transformation. This interaction prevents the growth of a unique plate and the transformation proceeds by successive nucleation of new plates. The friction associated to the movement of a single interface was also measured. From the experiments the relevant parameters which determine the hysteretic behaviour were identified. The hysteresis loops were computer simulated on the base of these parameters. The results showed a good agreement with the experimental observations.