Pseudoelastic Behavior of Fe 3 Ga Single Crystals with D0 3 Structure
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0980-II06-08
Pseudoelastic Behavior of Fe3Ga Single Crystals with D03 Structure Hiroyuki Y. Yasuda1,2, Mitsuhiro Aoki2, Kouki Fukushima2, and Yukichi Umakoshi2 1 Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka, 567-0047, Japan 2 Division of Materials and Manufacturing Science, Osaka University, 2-1, Yamada-oka, Suita, Osaka, 565-0871, Japan ABSTRACT Pseudoelastic behavior of Fe3Ga single crystals was investigated focusing on the dislocation structure and the phase constituent. Large pseudoelasticity of 5 % recoverable strain appeared in Fe3Ga single crystals sufficiently annealed in the D03 single-phase region, though a thermoelastic martensitic transformation never occurred in the crystals. In the D03-ordered crystals, uncoupled and paired 1/4[111] superpartial dislocations moved dragging the nearest-neighbor (NN) and next-nearest neighbor (NNN) anti-phase boundaries (APBs) during loading, respectively. During unloading, these APBs pulled back the superpartials resulting in large pseudoelasticity, which is similar to D03-ordered Fe3Al crystals. The dislocation configuration was closely related to the ordered domain structure developed in the D03 phase. Moreover, the precipitation of the thermally stable L12 phase was so slow that the metastable D03 phase developed even if the crystals were annealed in the (α+ L12) and (D03+ L12) phase fields in Fe-Ga equilibrium phase diagram. The metastable D03 phase also demonstrated large pseudoelasticity of which recovery ratio was above 80 %. On the other hand, if the L12 phase precipitated by long time annealing in the (α+ L12) region, the reversible motion of 1/4[111] superpartials was suppressed by the L12 phase resulting in a decrease in recovery ratio. In addition, the crystals aged in the (α+ D03) phase region showed small strain recovery. INTRODUCTION It is well known that perfect pseudoelasticity is generally based on a thermoelastic martensitic transformation or twinning [1]. Otsuka et al. [2] termed the former and the latter as “transformation pseudoelasticity” and “twinning pseudoelasticity”, respectively. However, perfect pseudoelasticity of which recoverable strain is 5 % appeared in D03-ordered Fe3Al single crystals [3-8] irrespective of the martensitic transformation and twinning. In the crystals, 1/4[111] superpartials moved individually dragging the nearest-neighbor anti-phase boundaries (NNAPB) during loading. During unloading, the NNAPB pulled back the superpartials to decrease its energy resulting in complete pseudoelasticity. The pseudoelasticity of Fe3Al crystals is not included in the terminology proposed by Otsuka et al. [2]. So, we call the pseudoelasticity “APB pseudoelasticity” [6, 7]. Recently, we found that Fe3Ga single crystals with the D03 structure also demonstrated large pseudoelasticity at room temperature [9]. Since there were no martensites and twins at the temperature during loading up to 5 %, APB pseudoelasticity may appear in D03-ordered Fe3Ga crystals. Figure 1 (a) shows Fe-Ga
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