Rate-dependent hardening due to twinning in an ultrafine-grained magnesium alloy
Rate-dependent hardening due to twinning in an ultrafine-grained magnesium alloy
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DOI：
10.1016/j.actamat.2011.12.002
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发表时间：
2012-02-01
期刊：
影响因子：
9.4
通讯作者：
Mukai, T.
中科院分区：
文献类型：
--
作者：
Li, Bin;Joshi, Shailendra P.;Mukai, T.
在相对较低的温度（488 K）下以高的断面收缩率（近似25）对平均晶粒尺寸近似为1.0 μ m的超细晶（UFG）ZK 60镁合金进行挤压。研究了超细晶镁合金在应变速率为10（-4）~ 10（4）s（-1）的范围内的力学行为。在准静态（类似于10（-4）s（-1））和高速率（10（4）s（-1））区域中的应力-应变响应表现出特征S形轮廓，其是{10（1）over bar 2}< 10（1）over bar（1）over bar >拉伸孪晶的特征。此外，该S形轮廓在高速率下加重，表明孪生诱导硬化的速率效应。X射线衍射（XRD）和分析收到的和变形的微观结构表明，即使在准静态加载速率的孪生发生。这一观察结果与一些理论预测相反，这些理论预测表明，在低于临界晶粒尺寸的Mg中，孪晶的抑制比本工作中的大得多。从XRD分析，我们推断，孪晶的体积分数增加与施加的应变速率。透射电子显微镜观察的测试标本揭示高密度的非基底位错，这可能是由于激活这些滑移系统后孪生诱导的晶格重新取向。(C)2011 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
An ultrafine-grained (UFG) ZK60 Mg alloy with an average grain size of similar to 1.0 mu m was processed by extrusion at relatively low temperature (488 K) with a high area reduction ratio (similar to 25). The mechanical behavior of the UFG Mg alloy is investigated over strain rates spanning nearly eight decades (10(-4)-10(4) s(-1)). The stress-strain responses in the quasi-static (similar to 10(-4) s(-1)) and high rate (10(4) s(-1)) regimes exhibit the characteristic sigmoidal profile that is a signature of {10 (1) over bar2}< 10 (1) over bar(1) over bar > extension twinning. Further, this sigmoidal profile is accentuated at high rates, suggesting a rate effect of twinning induced hardening. X-ray diffraction (XRD) and analysis of the as-received and deformed microstructures indicate the occurrence of twinning even at the quasi-static rates of loading. This observation is contrary to some of the theoretical predictions that suggest suppression of twinning in Mg below critical grain sizes much larger than in the present work. From the XRD analysis we infer that the twin volume fraction increases with increasing applied strain rate. Transmission electron microscopy observations of the tested specimens reveal high density non-basal dislocations that may result from the activation of these slip systems following twinning-induced lattice reorientation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.