Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Max-Planck-Institut für Intelligente Systeme, D-70589 Stuttgart, Germany.
Nat Mater. 2015 Jul;14(7):707-13. doi: 10.1038/nmat4288. Epub 2015 May 18.
Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model.
线缺陷，又称位错，在晶体材料中普遍存在，是理解塑性变形和机械强度的核心，也是控制各种电子和光子材料性能的关键。尽管近一个世纪以来对位错结构和相互作用进行了研究，但由于合成和测试无缺陷原始晶体极具挑战性，因此无法对位错成核的能量学和动力学进行测量。本文报道了在经受单轴拉伸的高质量〈110〉Pd 纳米线中直接测量表面位错成核强度的实验。研究发现，尽管成核强度与尺寸和应变速率的相关性较弱，但发现了强烈的温度依赖性，这与成核受热涨落辅助的预测相符。本文还测量了原子尺度的激活体积，这不仅解释了超高的非热强度，还解释了实验中明显存在的、与温度相关的分散性，这一现象可以很好地用热激活模型来描述。
