Hydrogen is foreseen as a promising energy carrier that can control global warming by reducing CO₂ emissions. However, hydrogen is associated with an embrittlement phenomenon that imparts substantial damage to the infrastructure by reducing the ductility, fracture strength, strength bearing capacity, etc., of metallic components. Therefore, understanding hydrogen-induced crack initiation mechanisms in metals are of prime importance. Greater insights into this critical phenomenon are expected if the hydrogen-induced crack initiation can be correlated with the local microstructure and corresponding stress-strain state towards their propensity for hydrogen accumulation. With this motivation, in this work, crack initiation is studied for the uncharged and hydrogen charged nickel specimens during in-situ tensile loading under the scanning electron microscope. By assuming the material to be elastic at low strains, a novel approach is implemented for generating the microstructural stress maps through strain and stiffness tensor extracted at each point in the region of interest on the specimen surface using high-resolution digital image correlation (HR-DIC) and Euler angles (given by electron backscattered diffraction data), respectively. Based on this analysis at low strain, the crack initiation sites for uncharged and hydrogen charged nickel specimens are correlated with microstructural maps of maximum Schmid factor, elastic modulus in the loading direction, hydrostatic stress, von Mises stress, and triaxiality factor. The analysis highlighted two independent factors responsible for hydrogen enhanced decohesion (HEDE) based intergranular failure observed only at the random grain boundaries, (i) strain localization due to hydrogen enhanced localized plasticity (HELP) mechanism of hydrogen embrittlement, and (ii) hydrostatic stress-based hydrogen diffusion to the crack initiation sites. These critical insights thus can help to design hydrogen embrittlement resistant metals. In addition, the novel experimental approach can be used to calibrate advance micromechanical models while providing quantitative estimate of the hydrogen distribution in realistic metallic microstructure responsible for hydrogen-assisted crack initiation with deformation.

氢被认为是有前途的能源载体，可以通过减少CO ₂来控制全球变暖排放。然而，氢与脆化现象有关，该脆化现象通过降低金属部件的延展性，断裂强度，强度承载能力等而对基础设施造成实质性损害。因此，了解氢在金属中引起的裂纹萌生机理至关重要。如果氢诱导的裂纹萌生可以与局部微观结构和相应的应力-应变状态朝着其氢积累的倾向相关，则有望对该临界现象有更深入的了解。出于这种动机，在这项工作中，在扫描电子显微镜下研究了原位拉伸载荷过程中不带电和带氢的镍试样的裂纹萌生。通过假设材料在低应变下具有弹性，通过高分辨率数字图像相关性（HR-DIC）和欧拉角（由电子背散射衍射给出），通过一种新颖的方法来实现通过在试样表面感兴趣区域的每个点处提取的应变和刚度张量生成微观结构应力图数据）。基于这种在低应变下的分析，不带电和带氢的镍试样的裂纹萌生部位与最大施密特因子，加载方向的弹性模量，静水应力，冯·米塞斯应力和三轴性因子的显微组织图相关。分析强调了两个独立的因素，它们仅在随机晶界处观察到基于氢增强脱粘（HEDE）的晶间破坏，（i）由于氢增强了氢脆的局部可塑性（HELP）机理而引起的应变局部化，以及（ii）基于静水应力的氢扩散到裂纹萌生部位。因此，这些重要的见识可以帮助设计耐氢脆性的金属。此外，该新颖的实验方法可用于校准先进的微机械模型，同时提供定量的氢估计在实际的金属微观结构中的氢分布，该金属微观结构负责伴随变形的氢辅助裂纹的萌生。