Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role?
Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role?
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DOI：
10.1016/j.actamat.2013.07.056
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发表时间：
2013-11-01
期刊：
影响因子：
9.4
通讯作者：
Rappaz, Michel
中科院分区：
文献类型：
--
作者：
Kurtuldu, Gueven;Jarry, Philippe;Rappaz, Michel
Al-20%(wt.%)锌合金的等轴凝固表明，当加入微量的铬(1000ppm)时，合金中有大量的细晶以孪晶或近孪晶的形式存在。发现了几个具有五重对称多孪晶关系的近乎共同的<；110>；方向的相邻颗粒。这些发现是一个非常强烈的迹象，表明初生面心立方Al相形成于二十面体准晶或母体稳定的Al45Cr7相的晶核上，该相在其大的单斜晶胞中表现出几个五重对称的积木。热力学计算和颗粒有时显示出与所谓的互锁二十面体相容的取向，进一步支持了它们。这些结果很重要，不仅因为它们解释了铝合金中孪晶枝晶的形核机制(尽管最近的几项研究在过去60年里一直不清楚)，还因为它们发现了铝合金中迄今被忽视的形核机制，这也适用于其他金属系统。(C)2013 Acta Materialia Inc.由Elsevier Ltd.出版。保留所有权利。
The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or near-twin, relationship with their nearest neighbors when minute amounts of Cr (1000 ppm) are added to the melt. Several occurrences of neighboring grains sharing a nearly common < 1 1 0 > direction with a fivefold symmetry multi-twinning relationship have been found. These findings are a very strong indication that the primary face-centered cubic Al phase forms on either icosahedron quasicrystals or nuclei of the parent stable Al45Cr7 phase, which exhibits several fivefold symmetry building blocks in its large monoclinic unit cell. They are further supported by thermodynamic calculations and by grains sometimes exhibiting orientations compatible with the so-called interlocked icosahedron. These results are important, not only because they provide an explanation of the nucleation of twinned dendrites in Al alloys, a topic that has remained unclear over the past 60 years despite several recent investigations, but also because they identify a so far neglected nucleation mechanism in aluminum alloys, which could also apply to other metallic systems. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.