Study on Fatigue Failure of Alloyed Cu Bicrystals by means of in-situ SEM Observation

晶界结构是影响晶界滑移、晶界腐蚀和晶界应力腐蚀开裂等晶界相关现象的决定性因素之一，已被广泛认为具有重要的工程意义。除了这些现象外，材料的疲劳行为预计对GB所含的结构也很敏感。为了将疲劳性能与GB结构联系起来，对铜模型双晶进行了GB结构的疲劳试验和模拟。对具有纵向扭转边界的铜双晶的疲劳研究结果总结如下：(1)塑性应变在晶界处的不相容会导致晶界附近的高内应力，并明显促进晶间疲劳裂纹的形核。(2) GB影响区是阻止晶内裂纹扩展的强大屏障。利用取向关系接近SIGMA3（111）的铜双晶对GB裂纹的偏离角依赖性进行实验，得到以下结论：(1)在偏离角小于3‰的试样中，未观察到晶间裂纹扩展。另一方面，当偏差角增加到5‰时，疲劳裂纹往往沿着GBs扩展。因此，可以说铜的晶间疲劳裂纹对GB组织非常敏感。(2)滑移阶梯溶解模型同样适用于沿晶疲劳裂纹的扩展。(3)疲劳裂纹路径不仅由国标组织决定，而且由组成晶粒的滑移几何形状决定。针对[110]倾斜边界GB结构的分子动力学模拟结果总结如下：(1)低角GBs中晶格位错的排列与根据Burgers向量的差异预测的排列一致。(2)晶间取向角对GB能量的影响较大。低角边界的GB能量与Read-Shockley模型计算的理论值吻合较好。少

It has widely been accepted that a structure of grain boundary (GB) is one of the decisive factors affecting the GB-related phenomena such as the GB sliding, the GB corrosion and the GB stress-corrosion cracking, which are important for engineering purposes. In addition to these phenomena, fatigue behavior of materials is expected to be sensitive to the structure of the GB contained. In order to correlate the fatigue property with the GB structure, both fatigue experiments and simulations of the GB structures were carried out on the copper model bicrystals.1. The results of the fatigue investigation on copper bicrystal having a longitudinal twist boundary are summarized as follows.(1) The incompatibility of plastic strain at the GBs could induce high internal stresses in the vicinity of GBs, and apparently assists the nucleation of an intergranular fatigue crack.(2) The GB affected zone was a strong barrier against the propagation of the intragranular crack that was initiated at a free … More surface.2. In the experiments on the deviation angle dependence of the GB cracking using the copper bicrystals having the orientation relationship close to SIGMA3 (111), the following conclusions were obtained.(1) In the speciments having the deviation angles less than 3ﾟ, no any intergranular crack propagations were observed. On the other hand, the fatigue cracks often propagated along the GBs when the deviation angle increased up to 5ﾟ. Hence, it is can be said that the intergranular fatigue cracking in the copper is sensitive to the GB structure.(2) The slip step dissolution model can be applicable also for the propagation of the intergranular fatigue cracks.(3) Paths of the fatigue cracks were determined not only by the GB structure but also by the slip geometry of the constituent grains.3. The results of the molecular dynamics simulation focused on the GB structure of [110] tilt boundaries can be summarized as follows.(1) Arangements of lattice dislocations within low-angle GBs agreed well with those predicted from the differing at Burgers vector.(2) The estimated GB energy showed strong dependence on the misorientation angle between the grains. The GB energies of the low-angle boundaries were in good agreement with the theoretical values calculated from the Read-Shockley model. Less