Rate limiting deformation mechanisms of bcc metals in confined volumes
Rate limiting deformation mechanisms of bcc metals in confined volumes
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DOI：
10.1016/j.actamat.2019.01.020
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发表时间：
2019-03-01
期刊：
影响因子：
9.4
通讯作者：
Maier-Kiener, V.
中科院分区：
文献类型：
--
作者：
Kiener, D.;Fritz, R.;Maier-Kiener, V.
通过对钨和铬进行四个量级的尺度桥接实验，研究了微观结构对超细晶体心立方金属强度标度行为的影响。通过进行宏观压缩实验，纳米压痕和原位微压缩测试中的扫描电子显微镜，塑性变形的体积被彻底减少，直到实现从散装行为到单晶变形特性的过渡。的应力-应变行为和局部样品的变形特性有关的表观变形机制建立多晶体心立方金属。小尺寸，界面和自由表面上的变形行为的影响被认为是相对于单晶的情况。自由表面在小体积的分数增加明确地改变强度标度行为的依赖于晶间位错积累过程。此外，还根据应变率敏感性和激活体积等与速率和温度相关的特性分析了热激活变形。为了从机械上解释这些数据，开发了一个基于位错的模型，预测温度相关的激活体积。我们发现，热激活扭结控制的速率相关的性能低于临界温度的所有长度尺度和微观结构状态。(C)2019 Acta Materialia Inc.爱思唯尔有限公司出版
The influence of microstructure on the strength scaling behaviour of ultrafine-grained bcc metals is investigated by scale-bridging experiments spanning four orders of length on tungsten and chromium. By performing macroscopic compression experiments, nanoindentation and in-situ micro-compression tests in a scanning electron microscope, the plastically deformed volume was thoroughly reduced until a transition from bulk behaviour to single crystalline deformation characteristics was achieved. The stress strain behaviour and local sample deformation characteristics were related to apparent deformation mechanisms established for polycrystalline bcc metals. The influence of small dimensions, interfaces and free surfaces on the deformation behaviour is considered with respect to the single crystal situation. The increasing fraction of free surfaces in small volumes explicitly alters the strength scaling behaviour in dependence of the intergranular dislocation accumulation processes. Furthermore, thermally activated deformation was analysed based on rate- and temperature-dependent properties, such as strain-rate sensitivity and activation volume. To mechanistically interpret this data, a dislocation based model predicting the temperature dependent activation volume was developed. We find that thermally activated kinks control the rate dependent properties below the critical temperature for all length scales and microstructure states. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd.