Ideal maximum strengths and defect-induced softening in nanocrystalline-nanotwinned metals
Ideal maximum strengths and defect-induced softening in nanocrystalline-nanotwinned metals
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DOI：
10.1038/s41563-019-0484-3
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发表时间：
2019-11-01
期刊：
影响因子：
41.2
通讯作者：
Sansoz, Frederic
中科院分区：
文献类型：
--
作者：
Ke, Xing;Ye, Jianchao;Sansoz, Frederic
金属通过纳米级晶界和相干孪晶界的强化表现为最大强度，这种现象被称为霍尔-佩奇击穿。纳米晶和纳米孪晶材料的软化机制不同。在这里，我们报道了纳米晶-纳米孪晶Ag材料表现出与上述机制不同的两种强度转变。原子模拟显示，随着孪晶间距的减小，有三个不同的强度区域，分别为晶界决定的正向霍尔-佩奇强化（接近零霍尔-佩奇斜率）机制和由孪界缺陷引起的软化（负霍尔-佩奇斜率）机制。在7纳米以下的双间距范围内达到理想的最大强度。通过分离微量Cu杂质，合成了硬度为3.05 GPa-42%的纳米晶-纳米孪晶银。
Strengthening of metals through nanoscale grain boundaries and coherent twin boundaries is manifested by a maximum strength-a phenomenon known as Hall-Petch breakdown. Different softening mechanisms are considered to occur for nanocrystalline and nanotwinned materials. Here, we report nanocrystalline-nanotwinned Ag materials that exhibit two strength transitions dissimilar from the above mechanisms. Atomistic simulations show three distinct strength regions as twin spacing decreases, delineated by positive Hall-Petch strengthening to grain-boundary-dictated (near-zero Hall-Petch slope) mechanisms and to softening (negative Hall-Petch slope) induced by twin-boundary defects. An ideal maximum strength is reached for a range of twin spacings below 7 nm. We synthesized nanocrystalline-nanotwinned Ag with hardness 3.05 GPa-42% higher than the current record, by segregating trace concentrations of Cu impurity (