Shape Memory Characteristics Associated with the B2⇄B19 and B19⇄B19' Transformations in a Ti-40Ni-10Cu (at.%) Alloy

Abstract

The B2⇄B19 and B19⇄B19' transformations in a ternary 50Ti-40Ni-10Cu (at.%) alloy were investigated by means of electrical resistivity measurements, differential scanning calorimetry and constant load thermal cycling tests, and they were compared with the B2⇄R and B2⇄B19' transformations in a thermo-mechanically treated binary 49.8Ti-50.2Ni alloy. The B2⇄B19 transformation in the ternary alloy under load took place within a narrow temperature range (2 to 5 K), whereas the B19⇄B19' transformation took place over a wide temperature range (>80K). The transformation start temperature of B2→B19 transformation increased with increasing applied stress, but that of B19→B19' remained unchanged with stress when the stress was below 30 MPa. The stress dependence of the transformation start temperature, transformation elongation and hysteresis of the B2⇄B19 transformations in the ternary alloy were 8.4 MPa/K in the reciprocal form (dσ/dT) where σ is the critical stress for inducing the transformation, 3.2% and 11 K, respectively. They were in-between those of the B2⇄R and B2⇄B19' transformations in the binary alloy. © 1990, The Japan Institute of Metals. All rights reserved.