Pseudoelasticity of D0 3 -Type Fe 3 Al and Fe 3 Ga-Based Alloys
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Pseudoelasticity of D03-Type Fe3Al and Fe3Ga-Based Alloys Hiroyuki Y. Yasuda1 and Yukichi Umakoshi2 1 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan 2 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan ABSTRACT The pseudoelastic behavior of Fe3Al and Fe3Ga alloys with the D03 structure is reviewed. In general, pseudoelasticity of shape memory alloys is based on a thermoelastic martensitic transformation. However, pseudoelasticity regardless of the martensitic transformation is found to take place in D03-ordered Fe3Al and Fe3Ga alloys. For instance, a 1/4 superpartial dislocation in Fe3Al alloys moves independently dragging an antiphase boundary (APB). During unloading, the APB pulls back the superpartial to decrease its energy resulting in pseudoelasticity, which is called “APB pseudoelasticity”. Moreover, D03-type Fe3Ga alloys were found to demonstrate three types of pseudoelasticity based on the dislocation motion, twinning and martensitic transformation depending on the chemical composition, degree of D03 order, loading axis, stress sense and deformation temperature. The mechanism of the pseudoelasticities in the D03-type intermetallics is discussed based on some in situ observations. The effects of chemical composition, deformation temperature and crystal orientation on the pseudoelastic behaviors are also discussed. INTRODUCTION Alloys such as Ti-Ni and Cu-Al-Ni alloys exhibit shape memory effect and pseudoelasticity which are generally based on a thermoelastic martensitic transformation [1]. For instance, the stress-induced martensitic transformation and the reverse one during loading and unloading result in pseudoelasticity, respectively. This phenomenon is called “transformation pseudoelasticity”. By the transformation pseudoelasticity in TiNi alloys, 8 % of applied strain can be recovered during unloading and therefore, the alloys have been used as antennas of portable phone and eyeglass frames [1]. However, Fe3Al [2-18] Figure 1. Unit cell of the and Fe3Ga [19-24] alloys with the D03 structure (Fig. 1) can D03 structure. demonstrate pseudoelasticity even if the martensitic transformation does not occur. It is strongly suggested that the pseudoelasticity of D03-ordered Fe3Al alloys is closely related to a reversible motion of dislocations dragging an antiphase boundary (APB) [4-9, 11-18]. Moreover, it is also interesting to note that three types of pseudoelasticities based on dislocation motion, deformation twining and martensitic transformation were found to appear in Fe3Ga alloys with the D03 structure [21-24]. This paper reviews recent progress in our understanding of the pseudoelasticity in D03-type Fe3Al and Fe3Ga alloys.
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PSEUDOELASTICITY OF D03-TYPE Fe3Al ALLOYS Proposed model for the pseudoelasticity in Fe3Al alloys Figure 2 shows Fe-Al binary phase diagram recently proposed by Ikeda et al. [25]. The D03 single-phase region extends over wide Al composition range.
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