Three strategies to achieve uniform tensile deformation in a nanostructured metal
Three strategies to achieve uniform tensile deformation in a nanostructured metal
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DOI：
10.1016/j.actamat.2003.12.022
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发表时间：
2004-04-05
期刊：
影响因子：
9.4
通讯作者：
Ma, E
中科院分区：
文献类型：
--
作者：
Wang, YM;Ma, E
在晶粒度为100 nm的纳米结构金属中，位错机制仍然是控制塑性变形的主要机制。这些材料类似于经历了大量冷加工的粗晶材料，不能再经历正常金属的几个应变硬化阶段，因此容易受到塑性不稳定性的影响，如拉伸缩颈。对于加工和应用来说，控制这种不均匀的塑性变形显然是重要的，而且往往是必要的。本文以等通道转角挤压的纯铜为模型，论证了在纳米结构金属中实现相对较大的稳定拉伸变形的三种策略。第一种方法使用所有原位形成的类复合材料微结构，如双峰晶粒度分布，对材料进行应变硬化，获得大的均匀拉伸应变，同时保持纳米结构带来的大部分强化。在第二种途径中，变形是在低温下进行的，例如77K。由于抑制了动态回复，材料重新获得了加工硬化的能力。结果是实现了均匀的伸长率，同时提高了低温下的强度。第三种方法利用了纳米结构铜的流动应力的高应变率敏感性，特别是在低应变率下。利用应变率硬化油拉伸变形的稳定化效应，在没有应变硬化的情况下，可以获得接近均匀的应变。我们还讨论了这些方法所涉及的变形机制，以评估它们对晶粒度远低于100 nm的纳米晶金属的适用性，在这些纳米晶金属中，正常的位错活动被严重抑制。(C)2003年Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
In nanostructured metals with grain sizes of the order of 100 nm, dislocation mechanisms remain dominant in controlling plastic deformation. These materials, similar to their coarse-grained counterparts that have been subjected to heavy cold work, can no longer go through the several strain hardening stages of normal metals and are hence susceptible to plastic instabilities Such as necking in tension. For processing and applications, it is obviously important and often necessary to control such inhomogeneous plastic deformation. Here we demonstrate three strategies to achieve relatively large stable tensile deformation in nanostructured metals, using the pure Cu processed by equal channel angular pressing as a model. The first approach uses ail ill situ formed composite-like microstructure, such as a bimodal grain size distribution, to impart strain hardening to the material and attain large uniform tensile strains while maintaining the majority of the strengthening brought forth by nanostructuring. In the second route, deformation is conducted at low temperatures, such as 77 K. The material regains the ability to work harden due to suppressed dynamic recovery. Uniform elongation is achieved as a result, together with an elevated strength at the cryogenic temperature. The third method takes advantage of the elevated strain rate sensitivity of the flow stress of the nanostructured Cu, especially at slow strain rates. Using the stabilizing effects of strain rate hardening oil tensile deformation, nearly uniform strains call be acquired ill absence of strain hardening. We also discuss the deformation mechanisms involved in these approaches to assess their applicability to nanocrystalline metals with grain sizes well below 100 run, where normal dislocation activities become severely suppressed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.