不同时效态3J21合金疲劳行为

Fatigue Behavior of 3J21 Alloy at Different Aged States

在MTS万能实验机上对室温大气环境下欠时效态、峰时效态和过时效态3J21合金的疲劳行为进行研究,并采用扫描电镜(SEM)对宏观断口及微观断口进行分析。结果表明:不同时效态疲劳裂纹均呈穿晶扩展,欠时效态3J21合金疲劳裂纹萌生寿命最长,扩展途径比较曲折,扩展速率最小,表现出最大的疲劳裂纹扩展抗力,疲劳寿命最长。而过时效态3J21合金的疲劳裂纹萌生寿命最短,沿晶扩展的比例增加,扩展途径相对平直,扩展速率最大,裂纹扩展抗力最小,疲劳寿命最低;峰时效态合金介于两者之间.不同时效态的疲劳断口均由疲劳源、疲劳裂纹扩展区和瞬断区组成。在低速扩展区,欠时效态断口呈现小平面,峰时效态和过时效态断口呈现冰糖状花样,在中速扩展区均未看到长的疲劳条纹,仅发现个别细小的疲劳条纹。

The fatigue behavior of under-aged,peak-aged and over-aged 3J21 alloy were testly by using MTS testing machine. The macrographs and micrographs of fatigue fracture were analyzed by Scanning Electron Microscopy （SEM）. The results show that the fatigue crack growth for different aged alloys is all transgranular. The fatigue crack initiation life of under-aged 3J21 alloy is the longest, the fatigue crack growth track is zigzag, the fatigue crack growth rate is the slowest the fatigue crack growth resistance is maximal the fatigue life is the longest. However the fatigue crack initiation life for over-aged alloy is the shortest. The proportion of growing along intercrystalline for over-aged alloy gradually increases; Its crack track is straighter; The fatigue crack growth rate is the fastest, its fatigue crack growth resistance is the lowest. The fatigue life is the shortest. The fatigue behavior of peak-aged alloy is between that of the two aged state alloys. The fatigue fracture consists of fatigue source, fatigue crack growth area and instantaneously fractured area of different states. In low growing area, the fatigued fracture of under-aged shows small plane. The fatigue fracture of peak-aged and over-aged shows sugar candy pattern. In middle growth area, the long fatigue striations were not inspected except small individual fatigue striations.