Assessment of residual stress fields at deformation twin tips and the surrounding environments

Stress fields close to twin tips and the associated local neighbourhoods of a hexagonal close-packed (HCP) polycrystal were studied in detail. For this purpose, a coarse grain textured Zircaloy-2 sample was firstly strained uniaxially in a macroscopic direction that favours tensile twin formation. The sample was then unloaded and residual elastic strains and lattice rotations measured using the high-resolution electron backscatter diffraction (HR-EBSD) technique. Measured elastic strain maps of various clusters of grains including parent and twin pairs were then analysed. Stress, dislocation density, and their associated concentrations close to twin tips, within twins, in the immediate neighbouring grain, at the intersection of two twins, and within parent grains were investigated. It is shown that the stress field at the twin tips varies as a function of local neighbourhood. High stress, lattice rotation, and dislocation density concentrations were generally observed close to twin tips both within twins and within the immediate neighbouring grains. It is shown that dislocation density concentration is maximum at the intersection of two twins which can potentially provide susceptible site for crack nucleation. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd.

详细研究了六方密堆积（HCP）多晶体孪晶尖端附近的应力场以及相关的局部区域。为此，首先将具有粗晶粒织构的锆合金 - 2样品在有利于拉伸孪晶形成的宏观方向上进行单轴拉伸应变。然后卸载样品，并使用高分辨率电子背散射衍射（HR - EBSD）技术测量残余弹性应变和晶格旋转。接着分析了包括母晶和孪晶对在内的各种晶粒簇的测量弹性应变图。研究了孪晶尖端附近、孪晶内部、紧邻的晶粒内、两个孪晶相交处以及母晶内部的应力、位错密度及其相关浓度。结果表明，孪晶尖端的应力场随局部区域的不同而变化。通常在孪晶内部以及紧邻的晶粒内靠近孪晶尖端处观察到高应力、晶格旋转和位错密度集中。结果还表明，在两个孪晶相交处位错密度集中最大，这可能为裂纹形核提供敏感位置。（C）2015 Acta Materialia Inc.由爱思唯尔有限公司出版。