Stress serration and arch-shaped Lüders stress plateau behaviour of Ti–50.8 at% Ni wire prepared by selective electrical resistance over-aging

Abstract

Joule heating of NiTi shape memory alloy wires is a commonly applied technique for heat treatment and shape setting in many applications. Another innovative use of this method is to produce functionally graded NiTi. In this study, NiTi wires with spatially varied shape memory characteristics along the length were created by electrical resistance over-aging of a Ni-rich superelastic NiTi alloy. The stress-strain behaviour of such wires exhibited some new and unique characteristics during the stress-induced martensitic transformation, including two discrete stress plateaus, stress serration during transition between the two stress plateaus and an arch-shaped stress plateau in the over-aged section. These unique features have direct implications to design using NiTi alloys and the underlying mechanisms are explained in this study.

Cyclic Stability of Ni44.8Cu5Ti45.2Hf5 and Zr‐Substituted Ni44.8Cu5Ti40.2Hf5Zr5 Medium‐Entropy Shape Memory Alloys

“…Miyazaki et al [ 58 ] investigated the stress–strain response of binary Ti 50.2 Ni 49.8 alloy after solution annealing at 1000 °C for 1 h at differen t testing temperatures above its A f temperature, but did not detect pseudoelastic effect in the alloy. Similar observations have also been made by Meng et al [ 59 ] and Cong et al [ 60 ] for solution annealed Ni‐rich binary NiTi alloys. The critical stress for slip is very low in the solutionized state; dislocations can then easily glide at stresses well below the critical stress for stress‐induced martensitic transformation.…”

Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

“…NiTi shape memory alloys (SMAs) are known to exhibit unique thermomechanical properties including the shape memory effect and pseudoelasticity [1]. These properties originate from the thermoelastic martensitic transformations in these alloys [2,3]. Owing to these remarkable properties, they have been used in many innovative designs, both in end product applications, such as low power actuators in automotive industry [4], wing morphing control in aerospace engineering [5], miniature actuators in microelectromechanical systems (MEMS) [6], actuators in robotics [7] and biomedical devices [8], and in novel materials designs, such as intermetallic composites [9], functionally graded designs [10][11][12][13], and smart architectured materials [14].…”