Direct evidence for local symmetry breaking during a strain glass transition.
Direct evidence for local symmetry breaking during a strain glass transition.
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DOI：
10.1103/physrevlett.112.025701
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发表时间：
2014-01
影响因子：
8.6
通讯作者：
Yumei Zhou;D. Xue;Ya Tian;Xiangdong Ding;Sheng-wu Guo;K. Otsuka;Jun Sun;X. Ren
中科院分区：
文献类型：
--
作者：
Yumei Zhou;D. Xue;Ya Tian;Xiangdong Ding;Sheng-wu Guo;K. Otsuka;Jun Sun;X. Ren
应变玻璃化转变是一种独特的纳米尺度的位移转变，在保持宏观对称性或平均结构不变的情况下，局部对称性破缺。它通常出现在马氏体系的“非马氏体”成分范围内。到目前为止，这种转变只有间接的证据，主要来自宏观测量和低分辨率的电子显微镜观察，而缺乏推测的局部对称性破坏和玻璃化转变的迟缓性质的直接证据。在这封信中，我们报道了对Ti50(Pd41Cr9)应变玻璃合金的高分辨率电子显微镜原位观察，并为这些关键问题提供了直接证据。我们的结果表明，在远高于应变玻璃化转变温度(Tg)的温度下，晶格基本上是没有扭曲的B2结构。在接近玻璃化转变温度时，随着纳米马氏体团簇的形成和长大，局域对称性逐渐破缺，纳米马氏体团簇的堆积周期为三个和四个平面间隔，但X射线衍射仪测得的平均结构仍为B2。这些纳米马氏体团簇在玻璃化转变温度下最终冻结。我们的结果不仅为应变玻璃的宏观性质提供了微观基础，而且为这类独特材料的一系列可能的应用提供了新的见解。
Strain glass transition is a unique nanoscale displacive transition with local symmetry breaking while maintaining the macroscopic symmetry or average structure unchanged. It usually occurs in the "nonmartensitic" composition range of a martensitic system. So far, only indirect evidence exists for such a transition, essentially from macroscopic measurements and low-resolution transmission electron microscopy observations, and there is a lack of direct evidence for the speculated local symmetry breaking and the sluggish nature of the glass transition. In this Letter we report in situ high-resolution transmission electron microscopy observations on a Ti50(Pd41Cr9) strain glass alloy and direct evidence for these key issues. Our results show that at temperatures well above the strain glass transition temperature (Tg), the lattice is essentially an undistorted B2 structure. With approaching Tg, the local symmetry breaking gradually occurs with the formation and growth of nanomartensite clusters with a combined stacking period of three and four plane intervals, but the average structure measured by x-ray diffraction remains B2. These nanomartensite clusters become finally frozen below Tg. Our results provide not only a microscopic basis for the macroscopic properties of strain glass, but also new insights into a range of possible applications of this unique class of materials.