Effect of Antiphase Boundary on the Pseudoelasticity in Fe 3 Al Single Crystals
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Effect of Antiphase Boundary on the Pseudoelasticity in Fe3Al Single Crystals Hiroyuki Y. Yasuda1,2,3, Kazuaki Nakano3, Masato Ueda3 and Yukichi Umakoshi2,3 1 Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan 2 Frontier Research Center, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan 3 Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan ABSTRACT Pseudoelasticity in Fe3Al single crystals with the D03 structure was investigated focusing on the type of thermally-induced antiphase domain boundaries (APDB) developed in the crystals. Fe3Al single crystals containing 23.0at%Al and 28.0at%Al were produced by a floating zone method. Fe-23.0at%Al single crystals with an appropriate heat treatment demonstrated perfect strain recovery during unloading after compression to plastic strains below 5.0%. In contrast, Fe-28.0at%Al single crystals exhibited little strain recovery. The ordering process and the type of thermal APDB depended strongly on the alloy composition. As a result, B2-type APDB having a displacement vector (R) of 1/4 was frequently observed in Fe-23.0at%Al, while D03-type APDB with R=1/2 was dominant in Fe-28.0at%Al. In Fe-23.0at%Al, the strong interaction between B2-type APDB and 1/4 superpartial dislocations led to the individual motion of the superpartials dragging deformation-induced antiphase boundary (APB). The restoring force due to the deformation-induced APB resulted in the pseudoelasticity in Fe-23.0at%Al single crystals. Moreover, the refinement of antiphase domains surrounded by B2-type APDB was found to be effective in the enhancement of shape recovery in the crystals. Thus, the thermally-induced APDB in the D03 phase played an important role in the pseudoelasticity in Fe3Al single crystals. INTRODUCTION It is well known that a large pseudoelasticity is closely related to a martensitic transformation [1]. However, Guedou et al. [2] found that Fe3Al single crystals in which martensitic transformation never occurs, demonstrated a giant pseudoelasticity. Kubin et al. [3] performed in-situ observation of dislocation motion in the crystals by TEM. In Fe3Al with the D03 structure, a superlattice dislocation with b= is known to dissociate into four superpartial dislocations with b=1/4 bounded by antiphase boundary (APB) [4]. In contrast, 1/4 superpartial dislocations in the single crystals moved individually dragging deformation-induced APB whose displacement vector (R) is 1/4 [3]. They concluded that the restoring force due to the deformation-induced APB resulted in the pseudoelasticity [3]. However, the reason is not clear why the superpartials move solely without forming a group. Moreover, further increase in recoverable strain will lead to a practical application of Fe3Al as a functional material. The ordering process of Fe-Al alloys is known to be very complicated as shown in Fe-Al
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