Polytypic transformations in Laves phases
Polytypic transformations in Laves phases
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DOI：
10.1016/j.intermet.2004.02.017
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发表时间：
2004-07-01
期刊：
影响因子：
4.4
通讯作者：
Hazzledine, PM
中科院分区：
文献类型：
--
作者：
Kumar, KS;Hazzledine, PM
Cr 2X（X = Ti、Zr、Hf、Nb或Ta）Laves相在高温下具有六方（2 H或4 H）结构，在室温下具有立方（3C）结构。它们的组成范围由它们的e/a比决定。在这些系统中的几个两相合金的实验观察表明，六方结构往往在室温下保留。随后在升高的温度下退火将亚稳的六方结构转变为稳定的立方结构。在单相的Cr2 Ti和Cr2 Ta中，转变非常缓慢，而在Cr2 Nb中，转变迅速。在两相合金中，相变几乎总是缓慢的（除了Cr-Nb系统），并伴随着成分的变化。透射电子显微镜观察是一致的转换所实现的同步剪切背后的滑动同步shockley位错。描述了同步剪切机制，并从两相合金中的长程扩散和单相合金中同步冲击位错的迁移率的角度讨论了相变动力学。(C)2004 Elsevier Ltd.保留所有权利。
The Cr2X (X = Ti, Zr, Hf, Nb or Ta) Laves phases have the hexagonal (2H or 4H) structure at high temperatures and the cubic (3C) structure at room temperature. Their compositional ranges are dictated by their e/a ratios. Experimental observations of two-phase alloys in several of these systems demonstrate that the hexagonal structure is often retained at room temperature. Subsequent annealing at elevated temperature transforms the metastable hexagonal structure to the stable cubic structure. In single-phase Cr2Ti and Cr2Ta, the transformation is extremely sluggish whereas in Cr2Nb, it is rapid. In two-phase alloys, the transformation is almost always sluggish (except in the Cr-Nb system) and is accompanied by compositional changes. Transmission electron microscopic observations are consistent with the transformations being achieved by synchroshear behind glissile synchroshockley dislocations. The synchroshear mechanism is described and the transformation kinetics are discussed in terms of long-range diffusion in two-phase alloys and in terms of the mobility of synchroshockley dislocations in single-phase alloys. (C) 2004 Elsevier Ltd. All rights reserved.