Nano-sized twins induce high rate sensitivity of flow stress in pure copper
Nano-sized twins induce high rate sensitivity of flow stress in pure copper
复制标题
纳米尺寸的孪晶在纯铜中引起流动应力的高速率敏感性
DOI：
10.1016/j.actamat.2005.01.031
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发表时间：
2005-04-01
期刊：
影响因子：
9.4
通讯作者：
Suresh, S
中科院分区：
文献类型：
--
作者：
Lu, L;Schwaiger, R;Suresh, S
我们研究了含有不同体积分数纳米尺寸孪晶但具有相同平均晶粒尺寸的多晶铜的流动应力的速率敏感性和强化程度。通过脉冲电沉积制备试样，其中通过改变工艺参数系统地改变孪晶的浓度。深度传感仪器压痕实验在加载速率跨越三个数量级的试样上具有较高的密度的孪晶（孪晶lamellum宽度类似于20 nm）显示高达7倍的增加率的敏感性硬度相比，基本上无孪晶纯铜相同的晶粒尺寸。相同晶粒尺寸的孪晶密度的降低（孪晶层宽度类似于90 nm）也导致速率敏感性和硬度的显著降低。高密度的纳米级孪晶的存在也被认为赋予显著的硬度，这与在纳米晶粒Cu中实现的硬度相当。在透射电子显微镜下对具有纳米级孪晶的压痕Cu的压痕后分析揭示了形变诱导的共格孪晶界（CTBs）的位移、沿CTBs的台阶和凹凸沿着CTBs的形成以及CTBs处位错的阻塞。这些过程似乎显着影响塑性流动的热激活体积的演变，这是一些三个数量级小于已知的微晶铜。透射电子显微镜还揭示了CTBs与高密度的位错碎片和点的可能性，位移CTBs可能作为障碍位错运动，他们也可能提供源位错成核，特别是附近的应力集中，非常像晶界。这些变形趋势的可能后果进行了探讨。(c)2005 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
We have investigated the rate sensitivity of flow stress and the extent of strengthening in polycrystalline copper containing different volume fractions of nano-sized twins, but having the same average grain size. The specimens were produced by pulsed electrodeposition, wherein the concentration of twins was varied systematically by varying the processing parameters. Depth-sensing instrumented indentation experiments performed at loading rates spanning three orders of magnitude on specimens with the higher density of twins (twin lamellae width similar to 20 nm) revealed an up to sevenfold increase in rate-sensitivity of hardness compared to an essentially twin-free pure Cu of the same grain size. A reduction in twin density for the same grain size (with twin lamellae width similar to 90 nm) also resulted in a noticeable reduction in rate-sensitivity and hardness. The presence of a high density of nano-scale twins is also seen to impart significant hardness, which is comparable to that achieved in nano-grained Cu. Post-indentation analyses of indented Cu with nano-scale twins in the transmission electron microscope reveal deformation-induced displacement of coherent twin boundaries (CTBs), formation of steps and jogs along CTBs, and blockage of dislocations at CTBs. These processes appear to significantly influence the evolution of thermal activation volume for plastic flow which is some three orders of magnitude smaller than that known for micro crystalline Cu. Transmission electron microscopy also reveals CTBs with a high density of dislocation debris and points to the possibility that displaced CTBs may serve as barriers to dislocation motion and that they may also provide sources for dislocation nucleation, especially near stress concentrations, very much like grain boundaries. Possible consequences of these trends for deformation are explored. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.