Three strategies to achieve uniform tensile deformation in a nanostructured metal

被引:863
作者
Wang, YM [1 ]
Ma, E [1 ]
机构
[1] Johns Hopkins Univ, Dept Mat Sci & Engn, Baltimore, MD 21218 USA
关键词
nanostructured materials; tensile property; deformation twins; strain rate sensitivity; temperature;
D O I
10.1016/j.actamat.2003.12.022
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
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.
引用
收藏
页码:1699 / 1709
页数:11
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