Xing Xiao, Deng Gonglin, Zhang Hao, Cui Gan, Liu Jianguo, Li Zili, Wang Bingying, Li Shouqin, Qi Chao
College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266500, China.
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
Materials (Basel). 2020 Nov 4;13(21):4949. doi: 10.3390/ma13214949.
In the current study, the effect of hydrogen atoms on the intergranular failure of -iron is examined by a molecular dynamics (MD) simulation. The effect of hydrogen embrittlement on the grain boundary (GB) is investigated by diffusing hydrogen atoms into the grain boundaries using a bicrystal body-centered cubic (BCC) model and then deforming the model with a uniaxial tension. The Debye Waller factors are applied to illustrate the volume change of GBs, and the simulation results suggest that the trapped hydrogen atoms in GBs can therefore increase the excess volume of GBs, thus enhancing intergranular failure. When a constant displacement loading is applied to the bicrystal model, the increased strain energy can barely be released via dislocation emission when H is present. The hydrogen pinning effect occurs in the current dislocation slip system, <111>{112}. The hydrogen atoms facilitate cracking via a decrease of the free surface energy and enhance the phase transition via an increase in the local pressure. Hence, the failure mechanism is prone to intergranular failure so as to release excessive pressure and energy near GBs. This study provides a mechanistic framework of intergranular failure, and a theoretical model is then developed to predict the intergranular cracking rate.
在当前研究中，通过分子动力学（MD）模拟研究了氢原子对α铁沿晶破坏的影响。利用双晶体体心立方（BCC）模型将氢原子扩散到晶界中，然后对模型进行单轴拉伸变形，研究了氢脆对晶界（GB）的影响。应用德拜-瓦勒因子来说明晶界的体积变化，模拟结果表明，晶界中捕获的氢原子会增加晶界的过量体积，从而增强沿晶破坏。当对双晶体模型施加恒定位移载荷时，存在氢时增加的应变能几乎不能通过位错发射释放。氢钉扎效应发生在当前的位错滑移系统<111>{112}中。氢原子通过降低自由表面能促进开裂，并通过增加局部压力增强相变。因此，破坏机制易于沿晶破坏，以便在晶界附近释放过大的压力和能量。本研究提供了沿晶破坏的机理框架，然后建立了一个理论模型来预测沿晶开裂速率。
