铝锂合金2198-T8高周疲劳性能及其裂纹萌生机理

Al-Li 2198-T8 alloy high cycle fatigue properties and its crack initiation mechanisms

摘要:

摘要：选用第三代铝锂合金2198-T8材料，对其力学以及高周疲劳性能进行了研究。相对于同系列不同时效状态或者其它航空铝合金材料，2198-T8在抗拉强度和屈服强度上均有不同程度的提升，并具有较强的抗疲劳性能，但疲劳数据的离散性却随着施加应力的减小而增大。利用扫描电子显微镜（SEM）及其自带的能谱分析（EDS）功能对疲劳裂纹萌生机理进行深入研究。研究发现，位错的增殖、运动和塞积是2198-T8疲劳裂纹萌生的主要原因，疲劳裂纹易于从驻留滑移带（PSB）以及挤出带形成的粗糙区域萌生。不同应力状态下，由材料内部缺陷引起的疲劳断裂现象是致命的，对疲劳寿命有巨大影响，最高可使疲劳寿命降低90%以上。裂纹萌生机制的不同可引起疲劳寿命的较大变化，合理的解释了疲劳数据的离散性问题。

Abstract:

Abstract: A research on mechanics and high cycle fatigue properties of the third generation Al-Li alloy 2198-T8 has been carried out. Comparing with the same series Al-Li alloys with different heat treatments and other aluminum alloys used in airplanes, the material 2198-T8 shows a various improvement on tensile strength and yield strength and a better performance in ant-fatigue, but the dispersion of fatigue data increases with the decreasing stress level. In order to explore the internal mechanism of this phenomenon deeply, the advanced testing measurements including scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) have been applied. The results reveal that the propagation, the movement and the pileup of dislocations are the main reasons for fatigue crack initiation, and fatigue crack could be easily formed in the rough zone of persistent slip band (PSB ) and dislocation extrusion area. Under different stress states, the fracture caused by the material’s internal defect are fatal, having a huge impact on the fatigue life, which can reduce the fatigue life much more than 90%. Different crack initiation mechanisms can make the fatigue life changed greatly, which explains the problem of dispersion in fatigue data reasonably.