Thermal Cyclic Fatigue Behavior of Nanostructured YSZ/NiCrAlY Compositionally Graded Thermal Barrier Coatings

Abstract

In this research, thermal cyclic fatigue (TCF) behavior of a compositionally graded layer (CGL) nanostructured coating was investigated and compared with the TCF behavior of a micro-CGL coating. The layers, as a thermal barrier coating (TBC), were made from nanostructured and/or conventional micro-sized yttria-stabilized zirconia (YSZ) and NiCrAlY powders. According to the composition of each layer, a certain ratio of YSZ/NiCrAlY powder was mixed and deposited by air plasma spray process on IN 738-LC as a substrate. In order to investigate the effect of temperature on the lifetime of coatings, TCF tests were conducted at two different high temperatures (900 and 1100 °C). These tests were done by holding the samples at the mentioned temperatures for 1 h and then fast cooling to 100 °C by compressed air for 10 min. Microstructural evaluation showed that there were some differences between the damage mechanisms of these two groups of compositionally graded TBCs. The results also showed that the average thermal cyclic lifetime of nanostructured compositionally graded TBCs is approximately 1.6 times higher than that of the micro-one. Moreover, it was indicated that the presence of much more spinel oxide regions formed at higher temperature has a remarkable effect on the lifetime of compositionally graded TBCs.