Fabrication and evaluation of a "nickel-free" shape memory alloy

• Main Author: Chen, Yexin.
• Other Authors: Liu Yong
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/54772
• Institution: Nanyang Technological University

The issues of hypersensitivity and potential toxicity ofNi simulate the development of the new types of Ni-free shape memory alloys. Preliminary investigation on the phase transformation and the superelasticity of a new shape memory alloy is conducted in this research. Considering the requirements on biocompatibility and mechanical property, guided by D-electron alloy design method and Mo equivalent method, the composition is designed as Ti-4Mo-3Nb at.%. The alloy is produced by arc melting and its composition is examined by Energy dispersive spectrometer (EDS). In order to obtain the supersaturated solid solution, the alloy is quenched from 1173K into water. Differential scanning calorimetry (DSC) is used to detect the transformation temperatures of alloys and the results are as follows: As= 25°C, Af = 66°C, M.\. = 81°C, Mf = _8°C. X-ray diffraction (XRD) is used to confirm that the alloy consists of a" and f3 phases at the 24°C. The peaks in DSC curve decline as the test cycle increases and two explanations are proposed. Aging at 573K for 1800s and 573K for 7200s are conducted to investigate the effect ofheat treatment. In terms ofthe sample aged for 1800s, both the critical stress for inducing martensite (YSIM and the critical stress for slip (J"s are higher than the critical stress of the sample subjected to the solution treatment. For the alloy aged for 7200s, the stress can induce the martensite continually at a constant stress after the elastic deformation. Therefore, aging at 573K for 7200s can control (YSIM and (J"s in a good range.