Study of Grain Boundary and Dislocation Transmission based on a Finite-Deformation Framework with an Application to Description of Nanoindentation Tests

晶界在位错运动引起的金属塑性变形中起着重要作用。接近晶界的压痕测试还表明，在所谓的GB弹入事件中，发生了位错堆积，然后位错通过GB传输。这一建议将基于有限变形梯度晶体塑性框架来解决位错与晶界之间相互作用的复杂性以及晶界对位错运动的影响。热力学一致性模型包括能量控制分量和耗散控制分量，并首先伴随着一个屈服函数，该屈服函数控制与在晶界积累的位错密度相关的微位错，然后扩展到自动考虑相邻晶界上相邻晶体的相对取向偏差的影响。该模型是基于一种新的方法开发的，并在有限元软件ABAQUS中实现。数值计算工作由参考体心立方材料上的纳米压痕和高分辨率电子显微镜支持。利用Berkovich和球形压头的纳米压痕，研究了不同晶界错位时的晶界突入行为。纳米压痕实验将折衷广泛的速率和尺寸相关的研究，根据到GB的压痕距离和压痕方向来量化GB的弹入效应。此外，连续抛光和高分辨率电子背散射衍射(HR-EBSD)被用来评估残余压痕周围的局部取向梯度，用于在颗粒内部的压痕以及显示GB弹出的压痕。这项研究工作将基于理论和实验相结合的方法，对位错晶界相互作用进行全面的描述。

Grain boundaries (GBs) play an important role in the plastic deformation of metals carried out by the motion of dislocations. Indentation tests close to grain boundaries have also shown the occurrence of dislocation pile-up and then transmission of dislocations through GBs in a so called GB pop-in event. This proposal will address the complexity of interactions between dislocations and grain boundaries as well as the effect of grain boundaries on the dislocation motions based on a finite-deformation gradient crystal-plasticity framework. The thermodynamically consistent model includes the energetic and dissipative governing components and is first accompanied with a yield function controlling microtractions associated with the densities of dislocations accumulated at grain boundaries and then extended to incorporate automatically the effect of the relative misorientation of adjacent grains at the grain boundary. The model is developed based on a novel approach and implemented in the finite-element software ABAQUS. The numerical work is supported by nanoindentation and high resolution electron microscopy on reference bcc materials. The grain boundary pop-in behavior is studied for different grain boundary misorientations using nanoindentations with Berkovich and spherical indenters. The nanoindentation experiments will compromise a wide range of rate and size dependent studies, quantifying the GB pop-in effect in dependence of the indentation distance to GBs and the indenter orientation. Furthermore, sequential polishing and high resolution electron back scatter diffraction (HR-EBSD) is used to assess the local orientation gradients around the residual impressions for indentations within grain interior as well as indentations exhibiting the GB pop-in. This research work will provide a comprehensive description of the dislocation grain boundary interaction, based on a combined theoretical and experimental approach.