EFFECTS OF THERMAL CYCLING AND ANNEALING ON THE MARTENSITIC-TRANSFORMATION OF COLD-ROLLED NI48TI52 ALLOY

The martensitic transformation behavior of the Ni48Ti52 alloy rolled by the cold reduction percent of 23% was investigated by differential scanning calorimetry (DSC) in order to reveal effects of thermal cycling and annealing after cold-rolling. The cold-rolling results in a broad DSC peak due to the transformation, and the subsequent thermal cycling enhances the peak gradually. The annealing converts the transformation process into a two-stage transformation due to the new formation of an intermediate phase when the high-temperature phase is martensitically transformed to the low-temperature phase. It is thought that the defects produced by the rolling play an important role in the transformation behavior because of the migration and annihilation of defects during the thermal cycles and the annealing.