Optimization of strength and ductility in nanotwinned ultra-fine grained Ag: Twin density and grain orientations
Optimization of strength and ductility in nanotwinned ultra-fine grained Ag: Twin density and grain orientations
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DOI：
10.1016/j.actamat.2015.06.030
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发表时间：
2015-09-01
期刊：
影响因子：
9.4
通讯作者：
King, A. H.
中科院分区：
文献类型：
--
作者：
Ott, R. T.;Geng, J.;King, A. H.
采用磁控溅射法在较宽的沉积速率范围内制备了具有不同孪晶密度和取向的纳米孪晶超细晶Ag厚膜。的孪晶界（TB）的间距和取向，以及晶粒尺寸为不同的沉积条件下，其特征在于同步辐射X射线散射和透射电子显微镜（TEM）。结构表征结合单轴拉伸试验的独立膜揭示了一个大的增加，在屈服强度的薄膜沉积在高沉积速率没有任何伴随的变化TB间距-一种行为，这是没有在文献中报道。我们发现，在较低的沉积速率下沉积的膜表现出更随机取向的晶粒与较低的整体孪晶密度（平均在所有的晶粒）比更重的孪晶晶粒与强的< 111 >纤维织构在较高的沉积速率下沉积的膜。然而，在孪晶晶粒的TB间距，并没有表现出任何显着的依赖于沉积速率。强度和塑性对孪晶密度和取向的依赖性可以用两种不同的软变形模式来描述：（1）非孪晶晶粒和（2）不沿沿着生长方向取向的孪晶晶粒< 111 >。非孪晶晶粒提供相对低的抗滑移性，并因此提供降低的强度，而不以沿着生长方向取向的纳米孪晶晶粒< 111 >比以沿着生长方向取向的纳米孪晶晶粒更软< 111 >。我们已经发现，由纳米孪晶（类似于8-12 nm间距）和未孪晶晶粒的混合物组成的超细晶（150-200 nm）结构产生高强度和均匀拉伸延展性的最佳组合。(C)2015 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Nanotwinned ultrafine grained Ag thick films with different twin densities and orientations have been synthesized by magnetron sputtering with a wide-range of deposition rates. The twin boundary (TB) spacings and orientations as well as the grain size for the different deposition conditions have been characterized by both synchrotron X-ray scattering and transmission electron microscopy (TEM). Structural characterization combined with uniaxial tensile tests of the free-standing films reveals a large increase in the yield strength for films deposited at high deposition rates without any accompanying change in the TB spacing - a behavior that is not reported in the literature. We find that films deposited at lower deposition rates exhibit more randomly oriented grains with a lower overall twin density (averaged over all the grains) than the more heavily twinned grains with strong < 111 > fiber texture in the films deposited at higher deposition rates. The TB spacing in the twinned grains, however, does not show any significant dependence on the deposition rate. The dependence of the strength and ductility on the twin density and orientations can be described by two different soft deformation modes: (1) untwinned grains and (2) nanowinned grains that are not oriented with < 111 > along the growth direction. The untwinned grains provide relatively low resistance to slip, and thus decreased strength, while the nanotwinned grains that are not oriented with < 111 > along the growth direction are softer than nanotwinned grains that are oriented with < 111 > along the growth direction. We have revealed that an uftrafine-grained (150-200 nm) structure consisting of a mixture of nanotwinned (similar to 8-12 nm spacing) and untwined grains yields the best combination of high strength and uniform tensile ductility. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.