Grain size effects in hcp polycrystals: from GNDs to blocky alpha
Grain size effects in hcp polycrystals: from GNDs to blocky alpha
复制标题
hcp 多晶中的晶粒尺寸效应：从 GND 到块状 alpha
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
F. Dunne
中科院分区：
文献类型：
--
作者：
M. Cuddihy;Zebang Zheng;J. Gong;T. B. Britton;A. Wilkinson;F. Dunne
通常情况下，当在微米和纳米尺度上测试物体时，会看到“越小越强”的尺寸效应。当使用这些测试来复制和理解组件级性能时，例如在材料发现计划中，这具有重要的后果。在这项计算塑性研究中，我们遵循龚等人的微悬臂梁实验方法。使用长度尺度相关的晶体塑性模型确定尺寸相关的六方晶系晶体滑移强度和复制尺寸敏感性。本文根据位错堆积的机理，导出了使滑移系硬化所需的背应力项。对Ti-6Al单晶体模型微梁四点弯曲试验结果表明，该方法可以准确地确定与尺寸无关的滑移强度，但对尺寸强化效应的预测不足。这是由于平均的离散位错行为中的连续滑移规则内所需的晶体塑性配方的晶粒尺寸的影响，在多晶性能的系统研究已经进行了晶粒尺寸从微米级到毫米的变化。在微米尺度下，几何必要位错（GNDs）的存在导致长度尺度相关硬化，导致经典的长度尺度效应。在较长的长度尺度下，例如当晶粒尺寸成为韧带宽度的显著部分（1/20或更多）时，相对几何形状效应变得显著，导致对材料性质和行为的显著影响。这两个界限为我们理解部件性能和合金设计提供了重要贡献，特别是在核能用航空钛合金和块状α锆合金的冷驻留刻面疲劳方面。* 通讯作者：imperial.ac.uk
Typically a ‘smaller is strong’ size effect is seen when testing objects at the micro and nanoscales. This has significant consequences when using these tests to replicate and understand component level performance, for instance in materials discovery programmes. In this computational plasticity study, we follow the micro-cantilever experimental approach of Gong et al. for determination of sizedependent hcp crystal slip strengths and replicate size sensitivity using length scale dependent crystal plasticity modelling. A fundamental derivation of the back stress term required to harden slip systems according to the mechanism of dislocation pile up is introduced. Model micro-beam single crystals in Ti-6Al under four-point bending were examined which showed that the size-independent slip strength could be correctly determined but that the size-strengthening effect was under predicted. This was attributed to the averaging of discrete dislocation behaviour in to the continuum slip rule required within the crystal plasticity formulation A systematic study of grain size effects in polycrystal performance has been performed where the grain size was varied from micron scale to millimetres. At the micron scale, length scale-dependent hardening, from the presence of geometrically necessary dislocations (GNDs), leads to classical length scale effects. At longer length scales, such as when the grain size becomes a significant fraction (1/20 or more) of the ligament width, relative geometry effects become significant leading to marked impact on material properties and behaviour. These two bounds provide important contributions to our understanding of component performance and alloy design, particularly in cold dwell facet fatigue in aero titanium alloys and blocky alpha zirconium alloys for nuclear energy. * Corresponding author: m.cuddihy12@imperial.ac.uk
影响因子：
9.4
作者：
Tarleton, E.;Balint, D. S.;Wilkinson, A. J.
通讯作者：
Wilkinson, A. J.