Abstract

The transformation characteristics of a near-equiatomic polycrystalline Ni-Ti alloy in an annealed state (600C/30 min/air-cooling) were determined by DSC measurements in order to investigate the effect of repeated heating and cooling process through the martensitic transformation region. It was observed that transformation profiles exhibited qualitative differences depending on the number of executed heating and cooling cycles. Due to the increasing number of thermal cycles, the forward transformation changed from a one-stage (B2→B19’) to a two-stage (B2→R→B19’) reaction while the reverse martensitic transformation showed the one-stage character (B19’→B2), independently of the number of achieved cycles. The other thermal properties were also found to change with thermal transformation cycles. Based on the calorimetric results and literature studied, it is thought that observed changes in transformation characteristics can be attributed to the modifications of the alloy microstructure. In this case the introduced defects which are accumulated during the thermal cycles play an important role. WPŁYW PROCESU WIELOKROTNEGO NAGRZEWANIA I CHŁODZENIA NA CHARAKTERYSTYKI PRZEMIAN W STOPIE Ni-Ti

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