Shape memory characteristics of Ti-Ni-Mo alloys sintered by sparks plasma sintering

Abstract

Porous shape memory alloys have attracted great interest as low-weight materials with high energy dissipation properties. In the biomedical field, owing to their biocompatibility and their promise to exhibit high strength and low modulus, porous Ti-Ni alloys have been tested as bone implant materials, successfully exhibiting a significant amount of bone ingrowth. In order to use the excellent superelastic property of shape memory alloys in many medical applications, the austenite transformation finish temperature (A(f)) must be about 37 degrees C which is human body temperature. In this study, the transformation temperature could be controlled through the substitution of Mo for Ni in a Ti-Ni alloy. For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, Ti50Ni49.9Mo0.1 and Ti50Ni49.7Mo0.3 shape memory alloy powders were prepared by gas atomization and the transformation temperatures and microstructures of those powders were investigated as a function of powder size. The dependence of powder size on the martensitic transformation temperature is also very small in the powders ranging from 25 to 150 mu m. The phase transformation temperatures of the porous specimens are almost the same as those of as-atomized powders and the A(f) of Ti50Ni49.9Mo0.1 and Ti50Ni49.7Mo0.3 porous specimens is 40.4 and 34.4 degrees C, respectively. According to compressive tests, the porous samples exhibit shape memory effect and it is found that the recovered stains of the Ti50Ni49.9Mo0.1 and Ti50Ni49.7Mo0.3 specimens are 1.5 and 2.0%, respectively. (C) 2012 Elsevier B.V. All rights reserved.