孔洞式缺陷对γ-TiAl合金断裂行为的影响

Effect of hole defect on fracture behavior of γ-TiAl alloy

采用分子动力学模拟方法研究了孔洞在不同温度、位置以及尺寸下对多晶γ-TiAl合金裂纹扩展的影响。结果表明,含孔洞式缺陷多晶γ-TiAl合金在1~750 K时为脆性解理断裂,1000 K和1200 K为韧性蠕变断裂。孔洞位于晶界和三叉晶界上时,合金更容易失效。与完美晶体相比,微孔洞的存在增加了多晶γ-TiAl合金的塑性。当孔洞半径大于1.0 nm时,多晶γ-TiAl合金的屈服应力和屈服应变急剧降低,材料发生失效的时间提前。孔洞尺寸的不同会影响材料的断裂方式,当孔洞半径R≤0.8 nm时,含孔洞多晶发生沿晶断裂;当R>0.8 nm时,多晶γ-TiAl合金的孔洞不断扩大逐步占满整个晶粒,发生穿晶断裂。

Molecular dynamics simulation was used to investigate the effect of hole defects on crack propagation of polycrystalline γ-TiAl alloy at different temperatures, hole locations and hole sizes. The results show that the polycrystalline γ-TiAl alloy with hole defect is of brittle cleavage fracture at 1-750 K, but of ductile creep fracture at 1000 K and 1200 K. The alloy is more likely to fail when the hole is located on the grain boundary and triple junction. Compared with the perfect crystal, the micropores increase the ductility of the polycrystalline γ-TiAl alloy. When the hole radius is larger than 1.0 nm, the yield stress and yield strain of the alloy decrease sharply, and the time of the alloy failure is advanced. The fracture mode is influenced by the hole size. Intergranular fracture occurs when the hole radius is less than or equal to 0.8 nm. When the hole radius is larger than 0.8 nm, the hole in the polycrystalline γ-TiAl alloy gradually expands and occupies the whole grain, and then transgranular fracture occurs.