CRITERIA OF TRANSFORMATION SEQUENCES IN NITI SHAPE-MEMORY ALLOYS

Near-equiatomic NiTi alloys are known to exhibit different transformat ion sequences associated with different thermomechanical treatment and testing conditions. Although a wide range of experimental data has be en accumulated through the past few decades of research, there has bee n a lack of understanding of the thermodynamic criteria for the occurr ence of various transformation sequences. This paper presents a phenom enological thermodynamic analysis of the transformation conditions and derives criteria for the sequences, which agree well with experimenta l observations.