Simultaneous high strength and mechanical stability of bcc Nb/Mg nanolaminates
Simultaneous high strength and mechanical stability of bcc Nb/Mg nanolaminates
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DOI：
10.1016/j.actamat.2022.118487
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发表时间：
2022-11-19
期刊：
影响因子：
9.4
通讯作者：
Pathak, Siddhartha
中科院分区：
文献类型：
--
作者：
Jain, Manish;Yaddanapudi, Krishna;Pathak, Siddhartha
虽然纳米复合材料已经证明了随着层厚度的减小，其强度增加了三倍甚至十倍，但它们的强度往往会超过临界层厚度。更令人惊讶的是，这种强度的增加几乎总是伴随着其破坏应变（延性）的降低。在这项工作中，我们报告的Nb/Mg纳米层压材料的强度和机械稳定性的同时改善，减少层厚度，很少报道的趋势，在纳米层压材料组成的纯金属。使用微柱压缩和纳米压痕实验，我们表明，包含体心立方（bcc）Mg假晶相的物理气相沉积（PVD）Nb/Mg纳米层压材料与包含六方密堆积（hcp）Mg相的那些相比，强度增加>60%，失效应变增加>80%。代替强度平台，Mg中的hcp到bcc相变导致纳米层压中的更新的强化机制，这是由从非相干界面到相干界面的变化引起的，沿着由于从各向异性hcp结构引入更具塑性各向同性的bcc材料而引起的失效应变的同时增加。使用高分辨率透射电子显微镜（HR-TEM），我们也证明了存在一个薄的bcc镁层在Nb/Mg界面在较大的层厚度时，镁主要是六方晶系。我们的研究结果表明，随着层厚度的减小，Nb/Mg纳米层压材料中的失效应变的增加可以与层中存在的假晶bcc Mg的近似体积分数相关。(c)2022 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
While bimetallic nanocomposites have demonstrated extraordinary - three to even ten-fold - gains in strength with decreasing layer thickness, their strengths tend to plateau beyond a critical layer thickness. More disappointingly, such increases in strength are almost always accompanied by a decrease in their strains to failure (ductility). In this work we report simultaneous improvements in both strength and mechanical stability of Nb/Mg nanolaminates with decreasing layer thicknesses, a trend seldom reported in nanolaminates consisting of pure metals. Using micro-pillar compression and nanoindentation experiments we show that physical vapor deposited (PVD) Nb/Mg nanolaminates that contain a body center cubic (bcc) Mg pseudomorphic phase demonstrate a >60% increase in strength and a >80% increase in strain to failure over those containing the hexagonal close packed (hcp) Mg phase. Instead of a strength plateau, the hcp-to-bcc phase transition in Mg results in a renewed strengthening regime in the nanolaminate caused by the change to a coherent interface from an incoherent one, along with a concurrent increase in strain-to-failure due to the introduction of a more plastically isotropic bcc material from an anisotropic hcp structure. Using high resolution transmission electron microscopy (HR-TEM) we also demonstrate the presence of a thin layer of bcc Mg at the Nb/Mg interface at larger layer thicknesses when Mg is predominantly hcp. Our results suggest that the increases in strain to failure in the Nb/Mg nanolaminates with decreasing layer thicknesses can be corelated to the approximate volume fraction of the pseudomorphic bcc Mg present in the layers.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.