Y. Wang, K. Otsuka, National institute for Materials Science, Japan, Tsukuba, Japan; X. Ren, National Institute for Materials Science, Tuskuba, Japan
Shape memory effect and superelasticity are usually found in alloys undergoing spontaneous martensitic transformation. Therefore, it is hard to imagine such novel properties can appear in an alloy without a martensitic transformation. In this study, however, we show shape memory effect and superelasticity can also occur in a “non-martensitic” Ti48.5Ni51.5 alloy [1], which has no spontaneous martensitic transformation upon cooling, but undergoes a “strain glass” transition [2]. The shape memory effect and superelasticity in strain glass were clarified experimentally by tensile measurement. The shape memory effect and superelasticity in strain glass stem from a stress-induced strain glass-to-martensite transformation and its reverse transformation, which was proved by in-situ x-ray diffraction experiment. More interestingly, physically parallel phenomenon has been found in ferroelectric relaxor, in which ferroelectric state can also be induced from a glassy relaxor state by applying an external electrical field. We also show experimentally that the property of stress-induced strain glass-to-martensite transformation exhibits remarkable similarity with that of field-induced relaxor-to-ferroelectrics transition. The origin of shape memory effect and superelasticity in strain glass is explained by a phenomenological model. The new shape memory effect and superelasticity in strain glass extends the regime and the composition range of shape memory alloys, and may lead to novel applications.
Reference:
[1] Y. Wang, X. Ren and K. Otsuka, Physical Review Letters, 97, 225703 (2006).
[2] S. Sarkar, X. Ren and K. Otsuka, Physical Review Letters, 95,205702(2005).
Summary: We show new shape memory effect and superelasticity,which do not rely on the spontaneous martensitic transformation, in a “non-martensitic” strain glass Ti48.5Ni51.5 alloy.
