Yield point elongation due to twinning in a magnesium alloy
Yield point elongation due to twinning in a magnesium alloy
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DOI：
10.1016/j.actamat.2011.11.022
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发表时间：
2012-02-01
期刊：
影响因子：
9.4
通讯作者：
Ghaderi, Alireza
中科院分区：
文献类型：
--
作者：
Barnett, Matthew R.;Nave, Mark D.;Ghaderi, Alireza
细晶粒镁合金AZ31在变形时表现出屈服伸长率，从而通过孪晶发生屈服。也就是说，在屈服之后，在应力应变曲线中存在平台。本文对形变试样中的孪晶进行了显微结构分析。一个主要的目的是解释屈服伸长率，特别是为什么它会随着晶粒尺寸的增加而降低并最终消失。它示出，在Luders屈服伸长孪晶在相邻的晶粒中启动孪晶事件，并以这种方式孪晶传播其方式逐步超过样品。这发生在大约每晶粒一个孪晶的孪晶频率下。一个标准的吕德斯应变的存在下，开发的基础上跨边界的孪生转移。结果表明，更高的吕德斯应变和应力，预计更细的晶粒尺寸。理解这种效应的关键是，它来自于吕德斯带传播的条件，即在恒定的外加应力值下，吕德斯带前沿的孪晶必须平均刺激前沿前方的新鲜材料中的一个孪晶。这里遵循的推导的一个重要部分是，在细晶粒样品中观察到的较高应力下，孪晶纵横比较大，因此对应于单个孪晶事件的晶粒水平处的应变在细晶粒样品中较高。(C)2011 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Fine-grained magnesium alloy AZ31 displays a yield elongation when deformed such that yielding occurs by twinning. That is, following yielding there is a plateau in the stress strain curve. The present paper presents a microstructural analysis of the twins in deformed samples. A major aim is to explain the yield elongation and in particular why it decreases and eventually disappears with increasing grain size. It is shown that during the Luders yield elongation twins initiate twinning events in neighbouring grains and in this manner twinning spreads its way progressively over the sample. This occurs at a twinning frequency of approximately one twin per grain. A criterion for the presence of a Luders strain is developed based on twin transfer across boundaries. It is shown that higher Luders strains and stresses are expected for finer grain sizes. The key to understanding the effect is that it arises from the condition for Luders band propagation whereby the twins on the Luders band front must stimulate, on average, one twin each within the fresh material ahead of the front, at a constant value of applied stress. An important part of the derivation followed here is that at the higher stresses seen in fine-grained samples, the twin aspect ratio is larger and consequently the strain at the grain level corresponding to a single twinning event is higher in finer-grained samples. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.