Greep-Fatigue Damage Evaluation of Coated Superalloy by A.C.Potential Method

对Inconel 738 LC涂层试样在1123 K空气中进行了快-快和慢-快应变波低周疲劳试验。对比了涂层试样和未涂层试样的低周疲劳寿命，并用交流电位法评价了蠕变疲劳损伤。得到的主要结论如下：1.涂层试样的低周疲劳寿命略小于未涂层试样，但两种试样的疲劳寿命相差不大。在快速-快速试验中，裂纹在涂层材料的外表面处开始并扩展到基底金属中。涂层试件的裂纹密度远小于未涂层试件。2.涂层试件的慢-快疲劳寿命约为快-快疲劳寿命的60%。对于涂层试样，在慢-快试验中，裂纹在涂层与基体材料之间的界面处萌生并扩展到基体材料中。3.交流电位法适用于涂层外表面和界面处裂纹的检测。低频交流电位对宏观裂纹的检测更为敏感。4.高频交流电位的增加与裂纹密度有关，低频交流电位的增加与裂纹最大长度有关。

This study carried out low cycle fatigue tests with fast-fast and slow-fast strain waves for Inconel 738LC coated specimens at 1123K in air. The low cycle fatigue life of coated specimens was compared with that of uncoated specimens and the creep-fatigue damage was evaluated by means of A.C.potential method. The main conclusions obtained are as follows.1.The low cycle fatigue life of coated specimens is slightly smaller than that of uncoated specimens but there is no large difference in the fatigue life between the two types of the specimens. Cracks were initiated at the outer surface of the coating materials and propagated into the base metal in fast-fast tests. The crack density of the coated specimen was far smaller in comparison with the uncoated specimens.2.The fatigue life in slow-fast tests was about 60% of that in fast-fast test for the coated specimens. For the coated specimens in slow-fast test, cracks were initiated at the interface between the coating and base materials and propagated into the base materials. Crack density was also far smaller in the coated specimens.3.A.C.potential method is proved to be applicable to the detection for the cracks initiated at the outer surface and the interface of coating. Low frequency of A.C.was more sensitive to the macro crack detection.4.The increase in the high frequency A.C.potential corresponds with the crack density while that of low frequency with the maximum crack length.