Abstract—

X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy have been used for the first time to carry out in situ systematical studies of the structure and phase transformations in the Heusler alloy Ni₅₄Mn₂₁Ga₂₅ with an L2₁ structure after megaplastic deformation by high pressure torsion. Deformation by high pressure torsion has been found to refine the polycrystalline structure of the alloy to a nanocrystalline and partially amorphous state. Total atomic disordering and stepwise structural-phase transformation according to a В2(bcc) → A2(bcc) → A1(fcc) scheme have been seen to occur with increasing the pressure (from 3 to 5 GPa) and the deformation degree (from two to five revolutions). Annealing at 573 K results in the devitrification of the amorphous phase. Annealing at 623 K and above has recovered the L2₁ structure. The size effect has been found to be responsible for the fact that cooling to 120 K suppresses martensite transformation in the nanostructured austenitic alloy with grain sizes less than 80 nm.

中文翻译：

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高压扭转导致的Heusler合金Ni 54 Mn 21 Ga 25的变形诱导原子无序和bcc→fcc转变

摘要-

首次使用X射线衍射分析，透射电子显微镜和扫描电子显微镜对具有L 2 ₁结构的Heusler合金Ni ₅₄ Mn ₂₁ Ga ₂₅的结构和相变进行了原位系统研究。经过高压扭转而发生巨塑性变形后。已经发现通过高压扭力变形使合金的多晶结构细化为纳米晶和部分非晶态。根据В2（bcc）→ A 2（bcc）→ A的总原子无序和逐步结构相变可以看到，随着压力（从3 GPa到5 GPa）和变形程度（从2到5转）的增加，发生了1（fcc）方案。573 K退火导致非晶相失透。在623 K及更高的温度下进行退火已恢复了L 2 ₁结构。已经发现尺寸效应是由于冷却至120K抑制了晶粒尺寸小于80nm的纳米结构奥氏体合金中的马氏体转变的事实。