Thermo-Mechanical Characteristics of Ti-Ni-Cu Shape Memory Alloy Fabricated by Pulse-Current Pressure Sintering Method
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Thermo-Mechanical Characteristics of Ti-Ni-Cu Shape Memory Alloy Fabricated by Pulse-Current Pressure Sintering Method Hideki Kyogoku, Takeshi Kadomura, Shinichiro Komatsu, Fusahito Yoshida1 and Toshio Sakuma2 Mechanical Engineering, Kinki University, Higashihiroshima, Hiroshima 739-2116, Japan 1 Mechanical Engineering, Hiroshima University Higashihiroshima, Hiroshima 739-8527, Japan 2 Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan ABSTRACT The Ti-Ni-Cu shape memory alloy by elemental powders was fabricated by means of a pulse-current pressure sintering method that can produce high-density sintered compacts in a very short sintering time. The fabrication conditions of Ti-Ni-Cu alloy and the influence of Cu content in Ti-Ni-Cu alloy on the tensile properties and thermo-mechanical characteristics were investigated. The relative density of the as-sintered compacts was around 97% at any Cu content. The microstructure, tensile properties and thermo-mechanical characteristics of the as-sintered compacts were improved greatly by performing a solid solution heat-treatment. The yielding behavior due to the stress-induced martensite in stress-strain curves of the alloy took place after elastic deformation at any Cu content. The deformation resistance of the alloys changed with Cu content, and it was lowest around 9at% in Cu content. The tensile strength and elongation of the alloy with Cu content around 9at% were more than 400 MPa and 6%, respectively. It was found that the thermo-mechanical behavior of the alloy becomes stable by performing cyclic deformation. INTRODUCTION Shape memory characteristics of Ti-Ni alloys are greatly influenced by alloy compositions, shape memory conditions and so on. In particular, since the fatigue properties and deformation behaviors of the Ti-Ni shape memory alloys can be improved by the ternary additions [1], the transformation behaviors and shape memory characterisdtics of Ti-Ni-Cu alloy have been extensively investigated. Nam et al. [2] reported that in the Ti-Ni alloy with Cu content less than 5at% the transformation of cubic B2 and monoclinic B19’ martensite phases takes place, in the alloy with Cu content from 5at% to 10at% both the transformation of B2 and B19’ and the transformation of B2, orthorhombic B19 martensite phase and B19’ take place, and in the alloy with Cu content more than 10at% the transformation of B2, B19 and B19’ takes place. Also, they reported that the influences of Cu content on the transformation behavior and mechanical properties of Ti-Ni-Cu powders fabricated by mechanical alloying [3-4]. The cyclic deformation characteristics of Ti-Ni-Cu alloys have been reported in detail by Strnadel et al. [5,6]. The authors [7-9] have reported on the fabrication of Ti-Ni shape memory alloy by a pulse-current pressure sintering method using elemental powders and the effect of fabrication conditions on thermo-mechanical characteristics of the Ti-Ni alloy compacts. There is, however, no literature on the thermo-mechanical characteris
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