Low-cycle fatigue of MCrAlY-coated superalloys: A fracture mechanics-based analysis

Abstract

A fracture mechanics-based method was proposed to quantify the low-cycle fatigue (LCF) life reduction of superalloys deposited with MCrAlY coating. A series of LCF tests were conducted under different temperatures to verify the accuracy of the model. The effect of the coating shows temperature-related behaviour. At 980°C, the coating reduced the LCF life of the samples. Furthermore, the coating-induced fatigue life reduction increased with the stress amplitude. However, at 850°C, the coating was beneficial to the fatigue life at low-stress amplitudes but harmful at high stress amplitudes. Based on the aforementioned data, a life-prediction model of the coated superalloy was proposed that agreed well with the test results.

Two aspects of high interfacial strength regarding the cracking behaviour of MCrAlY-coated superalloys

“…Subsequently, the interfacial crack deflects into the coating and substrate under cyclic loading. However, it should be noted that the substrate crack can also be caused by cracks on the surface of the coatings, which has been investigated in previous studies [44,45]. In this study, we only discuss the effects of interfacial cracks.…”

“…However, this conclusion might neglect the effect of coating cracks. During service, surface cracks in coatings have a significant effect on the failure of the coated samples [45]. The change in interfacial strength could influence the strength of the coatings, which should be investigated in future studies.…”