Effects of Cold Working and Heat Treatment on Transformation Temperature of Ti-41.7Ni-8.5Cu (at%) Shape Memory Alloy and Its Probabilistic Prediction

Abstract

The transformation temperatures of shape memory alloy vary with the composition and processing and manufacturing conditions of the alloy. The purpose of the present study is to clarify the effects of cold working and heat treatment on various transformation temperatures, and to estimate probabilistically the transformation temperatures by means of a model. The shape memory alloy used was Ti-41.7Ni-8.5Cu (at%), and the transformation temperatures were measured by the differential scanning calorimeter method (DSC method). The effects of processing and heat treatment on the transformation temperatures were investigated by changing the cold working ratio (10-40 %) and the heat treatment temperature (623-773 K), respectively. As a result, the transformation temperatures were found to decrease with increasing cold working ratio. The transformation temperatures were also found to increase with increasing heat treatment temperature. Therefore, the transformation temperatures were modeled by considering quantitatively the effects of the cold working ratio and the heat treatment temperature. A probabilistic prediction formula was proposed so that the reliability of the prediction may be estimated quantitatively.