Deformation Behavior Due to Stress-Induced Martensitic Transformation in TiNi Shape-Memory Alloy Wires

Abstract

The behavior of the interface between a parent phase and a martensitic phase and the lateral to longitudinal strain ratio due to the stress-induced martensitic transformation (SIMT) were investigated in the both regions of superelasticity (SE) and shape memory effect (SME) in TiNi shape-memory alloy wires through the tensile test. The Interface which appears due to SIMT during the loading process and its reverse transformation during unloading starts at both ends of a wire in the gripping parts and thereafter propagates towards the central part. When the two interfaces meet, SIMT completes. The behavior of SIMT under cyclic SE deformation does not change during cycling. The behavior of SIMT in the region of SE is similar to that in the region of SME. The lateral to longitudinal strain ratio due to SIMT and its reverse transformation is 0.43∼0.46. Poisson's ratio in a parent phase, a rhombohedral phase and a martensitic phase is 0.33∼0.34.