Trans-twin dislocations in nanotwinned metals
Trans-twin dislocations in nanotwinned metals
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DOI：
10.1016/j.scriptamat.2023.115348
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发表时间：
2023-02-16
影响因子：
6
通讯作者：
Lu, Lei
中科院分区：
文献类型：
--
作者：
Bu, Linfeng;Cheng, Zhao;Lu, Lei
材料的强度控制位错机制可以通过将流动应力分解为有效应力和背应力来阐明。最近的实验报告了纳米孪晶Cu的近似恒定的饱和有效应力约为100 MPa，纳米孪晶厚度范围小于100 nm [Z. Cheng等人，Proc. Natl. Acad. Sci. U.S.A. 119（2022）e2116808119]。这个令人惊讶的结果意味着有效应力是由跨越多个纳米孪晶层的长位错控制的，称为反式孪晶位错，而不是通常认为的限制在单个纳米孪晶层内的穿透位错。在这里，我们使用分子动力学来模拟跨多个纳米孪晶层的反式孪晶位错的形成和运动。我们表明，反式孪晶位错的相互连接部分可以在连续纳米孪晶片层中的波纹{111}滑动面上协调滑动，并且来自共格孪晶边界的阻力很小。我们的研究结果表明，有限的阻力滑移传输跨相干孪晶界可以设置一个下限的有效障碍间距阻碍位错滑移，从而决定了上限的饱和有效应力的纳米孪晶金属。这项工作为纳米孪晶金属的强度控制机制提供了新的认识。
The strength-controlling dislocation mechanism of a material can be illuminated by partition of the flow stress into its effective stress and back stress components. Recent experiments report a nearly constant saturated effective stress of about 100 MPa for nanotwinned Cu with a range of nanotwin thicknesses less than 100 nm [Z. Cheng et.al., Proc. Natl. Acad. Sci. U.S.A. 119 (2022) e2116808119]. This surprising result implies that the effective stress is controlled by the long dislocations spanning multiple nanotwin lamellae, termed trans-twin dislocations, rather than the commonly thought threading dislocations confined within individual nanotwin lamellae. Here we use molecular dynamics to simulate the formation and motion of trans-twin dislocations across multiple nanotwin lamellae. We show that the interconnected segments of a trans-twin dislocation can glide concertedly on the corrugated {111} slip planes in consecutive nanotwin lamellae with little resistance from coherent twin boundaries. Our results indicate that the finite resistance to slip transmission across coherent twin boundaries can set a lower limit of the effective obstacle spacing to hinder dislocation glide and thus dictate the upper limit of the saturated effective stress of nanotwinned metals. This work provides new understanding of the strength-controlling mechanism in nanotwinned metals.