原位观察1420Al-Li合金疲劳裂纹的“自抑制”

IN SITU SEM OBSERVAION OF SELF-ARRESTING OF FATIGUE CRACKS IN Al-Li ALLOY 1420 THICK PLATE

本文对1420Al－Li合金厚板采用紧凑拉伸、三点弯曲、电镜原位拉伸疲劳等方法，考察了不同取向的疲劳裂纹扩展行为，观测了长裂纹扩展路径形态、讨论了层状结构与材料疲劳性能之间的关系结果表明，层片的界面对板材的疲劳性能具有重要影响，在裂纹扩展过程中，层片与裂纹尖端相互作用，通过不同的外韧化作用使得1420合金裂纹扩展的阻力在不同取向出现显著差异．在L－T和T－S取向时，在△K为3－4和6－gMPa·m1／2范围内出现了裂纹扩展的“自抑制”

The effect of orientation on long fatigue crack propagation behavior was investigatedfor an aluminum-lithium alloy (1420) plate with 10 mm thickness at stress ratio of 0.1. The methodsused are three-point bending, compact tension and in situ pulsating fatigue in SEM. The in situ fatigueobservations were emphasized on crack path morphology and its closure during fatigue. It was indicatedthat 1420 of multi-layer microstructure can be regarded as an in situ laminated composite. The interfaceof the laminated metal matrix composite plays a significant role on the fatigue crack growth. The crackpath is governed by the weak interface to form zigzag with groups of minor cracks within the laminatedstructure, which results in the increase of the closure force. The crack propagation arresting is observed inthe △k range of 3 - 4 and 6 - 9 MPa·m1/2 for L - T, T - S orientations, respectively.