氢影响下纳米晶体晶界滑移和晶界三叉点裂纹形核模型

Grain Boundary Slip and a Grain Boundary Triple Junction Crack Nucleation Model for Nanocrystals Under the Influence of Hydrogen

在远场均匀拉伸载荷下,裂纹尖端会产生应力集中,与裂纹尖端相邻的晶界会承受较大的切应力,此切应力会导致晶界滑移.该文研究了氢和纳米晶界滑移对晶界裂纹形核、临界应力强度因子以及屏蔽效应的影响.应用连续分布位错方法给出了模型的理论解.结果表明:由于位错在晶界三叉点和滑移带尖端处的塞积,楔形裂纹会优先沿着晶界三叉点DC方向和晶界BD向上萌生,而且氢会使得裂纹萌生的总能量降低,氢浓度每增加1%,萌生最稳定裂纹的总能量大约降低1.86%.虽然晶界滑移会使得裂纹尖端的临界应力强度因子和屏蔽效应增大,但是氢使得临界应力强度因子降低.最后根据弱键理论,研究了氢对表面能的影响,氢浓度每增加1%,表面能降低5%.这一理论工作提供了氢和晶界滑移对材料微观断裂力学的新信息,有助于解释金属断裂的微观机理.

Under the far-field uniform tensile load,the crack tip will generate stress concentration,and the grain boundary adjacent to the crack tip will bear large shear stresses to cause nanograin boundary slip.The effects of hydrogen and nanoboundary slip on the crack nucleation,the critical stress intensity factor and the shielding action were investigated.The theoretical solution of the model was given with the continuous distribu-ted dislocation method.The results show that,the wedge cracks preferentially germinate along direction DC of the grain boundary triple junction and grain boundary BD due to the plugging of the dislocation at the grain boundary triple junction and the tip of the slip plane.Moreover,hydrogen decreases the total energy of crack initiation.When hydrogen concentration increases by 1%,the total energy of the most stable crack initiation will decrease by about 1.86%.Although the grain boundary slip increases the critical stress intensity factor and the shielding action at the crack tip,hydrogen will decrease the critical stress intensity factor.Finally,accord-ing to the hydrogen enhanced decohesion(HEDE)theory,the influence of hydrogen on surface energy was studied.With every 1%increase of the hydrogen concentration,the surface energy will decrease by 5%.This theoretical work provides new information on the microscopic fracture mechanics of materials caused by hydro-gen and grain boundary slip,and helps to explain the microscopic mechanism of metal fracture.