Structure and shape recovery characteristics of Ti-50.0%Ni thermomechanically treated industrial wire

Abstract
The effect of post-deformation annealing (PDA) temperature in a range 300 to 700°C and induced stain (3 to 24%) on shape recovery temperature range (SRTR) was studied for an industrial Ti-Ni wire. To determine the characteristic temperatures of martensitic transformations, a differential scanning calorimetry was used. SRTR was determined by the method of bending deformation followed by heating for shape recovery. The wire structure was studied by X-ray diffraction and TEM methods. The original structure of wire is a B19'- martensite or a mixture of B19', R -phase and B2- austenite containing a well-developed dislocation substructure. To obtain structure uniformity along the wire length, the PDA temperatures of 500-600°C are recommended. The SRTR at the wire of near-equiatomic Ti-Ni alloys produced by warm drawing can be controlled using PDA in the temperature range 400 to 700°C. SRTR in the 70-100°C range is achieved by means of PDA at 400 to 650°C (SRTR increases in this PDA range). With the increasing of induced strain from 5 to 24%, the high-temperature shape memory effect is appears and grows: a non-monotonic A_F growth from 90 to 150°C and SRTR broadening are observed. Shape recovery parameters of studied wire are high: the maximum completely recoverable strain of 4 - 5%, the maximum recoverable strain of 7 - 13%, and they can be controlled using PDA.