一种新型粉末高温合金的低周疲劳行为与寿命预测模型分析

Analysis of Low Cycle Fatigue Behavior and Life Prediction Model of a New Powder Superalloy

摘要:

对一种新型第三代粉末高温合金A3在700℃、应变范围0.8%～1.4%试验条件下的低周疲劳性能进行了研究,分析了材料的循环滞后回线、Massing特性、循环应力应变响应、应变-寿命关系等特性。采用Manson-Coffin模型、拉伸滞回能模型、三参数能量模型对疲劳寿命数据进行拟合预测,结果表明Manson-Coffin模型的寿命预测精度最高,在3倍分散带以内。用扫描电子显微镜对疲劳源区观察,结果表明：低应变时疲劳源数量上呈现单源,高应变时多源特征；随应变量增大,疲劳源位置趋向于试样表面,裂纹扩展区面积减小, 瞬断区面积增大。疲劳断口典型的三个区域观察结果表明：疲劳源四周存在较多河流状线,其为裂纹扩展方向,裂纹扩展区存在较多二次裂纹,瞬断区出现韧窝与解理断裂特征。A3合金的断裂模式主要为穿晶断裂。

Abstract:

In order to study the low-cycle fatigue behavior of a new powder superalloy A3, fatigue tests with total strain amplitudes from 0.6% to 1.4% at 700℃ were conducted. Fatigue test results were analyzed including cyclic stress-strain responses, Massing characteristics and strain-life curves. The fatigue life data were fitted by Manson-Coffin equation, Ostergren model and three-parameter energy method. The accuracy of fatigue life prediction obtained by Manson-Coffin equation is optimum. The micro-mechanisms were studied through scanning electron microscopy (SEM). As the strain amplitude gets larger, the number of fatigue sources increases, and the location of the fatigue source changes from the core of the sample to the surface, and the area of the crack propagation decreases while the ductile fracture zone increases. The observation of these three typical areas of fatigue fracture shows that light white river-like lines were found around the fatigue origin in the crack initiation zone which direct to crack propagation. Secondary cracks were found in the crack propagation zone. Dimples and cleavage fracture characteristics were found in the ductile fracture zone. The fatigue fracture mode of A3 alloy is mainly trans-granular.