Thermal cycling behavior of Yttria Stabilized Zirconia and Lanthanum Zirconate as graded and bilayer EB-PVD thermal barrier coatings

Abstract

Traditionally Yttria partially stabilized Zirconia (YPSZ) coatings are used as thermal barrier coatings (TBCs) on chambers. More and more often, they are applied on turbine blades. Investigations on some various materials with perovskite, spinel and pyrochlore structures have shown a great potential of Lanthanum Zirconate (pyrochlore) as thermal barrier coatings. In this work, Lanthanum Zirconate has been developed as a TBC using Electron Beam Physical Vapour Deposition (EB-PVD). TBCs deposited by EB-PVD exhibit a columnar grain microstructure, which is able to better balance the difference in thermal expansion between the base material and TBC during thermal cycle and hence improved the TBC lifetime. Two different coating architectures were developed for the TBCs. First a bilayer TBC consisting of YSZ and Lanthanum Zirconate was deposited. In the second approach a graded TBC with a transition from YSZ to Lanthanum Zirconate was deposited. The thermal cycling behavior of these coatings on Inconel Alloy 600 was investigated by a thermal cycling test at 1050 °C. Additionally, the coatings were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results of thermal cycling test showed an increase in the number of cycles before fatigue from 1380 cycles for YSZ to 3390 cycles for the graded YPSZ/Lanthanum Zirconate and 4140 cycles for the bilayer YSZ/Lanthanum Zirconate.