定向凝固DZ4合金的低周疲劳行为与稳定循环应力

 对定向凝固DZ4合金760℃和800℃下的低周疲劳和稳定循环应力应变行为进行了研究,并结合断口观察试验结果,对其疲劳裂纹的萌生与扩展进行了分析。结果表明,DZ4合金760℃和800℃下的低周疲劳属应力疲劳,其损伤以弹性损伤为主,弹性损伤与疲劳寿命具有很好的相关性。加载频率对DZ4合金760℃和800℃下的稳定循环应力均具有一定的影响,尤其是800℃时,各应变下的稳定循环应力均随加载频率的升高而减小。定向凝固DZ4合金高寿命低周疲劳裂纹易于萌生于试样内部或亚表面的柱状晶界,其疲劳裂纹的稳定扩展也较难形成典型的疲劳条带。

Low Cycle Fatigue Behavior and Steady Cycle Stress of Directionally Solidified DZ4 Superalloy

The low cycle fatigue (LCF) and steady cycle stress vs strain behavior of directionally solidified DZ4 superalloy at 760℃ and 800℃ are studied. Combining with the results of fracture observation, the fatigue crack initiation and propagation are analyzed. The results show that the LCF of DZ4 superalloy at 760℃ and 800℃ can be contribute to stress fatigue owing to the main elastic damage in LCF processing. The elastic damage has a favorite relativity with fatigue life. The loading frequency has an influence on steady cycle stress of DZ4 superalloy at 760℃ and especially 800℃ of all the steady cycle stress at different strain increasing with the loading frequency. The high life LCF cracks of DZ4 superalloy favorably initiate at the transverse segment of longitudinal grain boundary. And typical fatigue striation formation is difficult on fatigue crack steady propagation.