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通过开展低周疲劳试验,研究了镍基单晶高温合金DD6的疲劳微观损伤及断裂机制。结果表明:低温条件下DD6表现为起始硬化,饱和,然后软化至断裂,高温时试样则表现为起始软化。低应变下高温可降低单晶合金疲劳性能。低温下试样循环硬化程度比高温时高,高温下原子热激活行为降低了材料形变抗力。试样裂纹萌生位置有两种:一种在试样表面,另一种在晶体内部微孔处。裂纹扩展具有两个阶段:初始阶段扩展面非常平坦,仅有小量撕裂棱;扩展阶段则产生河流状花纹,扩展区内以疲劳辉纹形式扩展,最终进入瞬断区。
Through the low cycle fatigue test, the fatigue micro-damage and fracture mechanism of Ni-based single crystal superalloy DD6 were studied. The results showed that DD6 showed initial hardening, saturation at low temperature, then softened to fracture, while at high temperature, DD6 showed initial softening. High temperature at low strain can reduce fatigue properties of single crystal alloys. At low temperature, the degree of cyclic hardening is higher than that at high temperature, and the heat activation of atoms under high temperature reduces the material deformation resistance. There are two types of crack initiation sites: one on the sample surface and the other on the interior of the crystal. Crack propagation has two stages: the initial stage of expansion is very flat, only a small amount of tearing edge; the expansion phase is the river-like pattern, expanding the region to expand in the form of fatigue spikes, and finally into the instantaneous area.