Isothermal oxidation and thermal cyclic behaviors of YSZ and double-layered YSZ/La2Zr2O7 thermal barrier coatings (TBCs)

Abstract

TBCs provide protection of superalloy substrates against harsh environments in gas turbine engines. Typical TBCs consist of two main coating layers called bond and top coat. Recently, zirconates have become attractive top coat materials as an alternative to yttria stabilized zirconia (YSZ) due to their superior thermal properties. Zirconates are deposited on YSZ layer to decrease the thermal conductivity and to minimize the oxygen penetration. Furthermore, their high melting point as well as phase stability and sintering properties render them promising materials for TBC applications. In this regard, YSZ and YSZ/La2Zr2O7 top coats were deposited using EB-PVD technique on HVOF-CoNiCrAlY bond coated Inconel 718 superalloy, in the present research. TBCs were exposed to isothermal oxidation tests in high temperature furnace at 1000 degrees C with different time periods and also, they were subjected to furnace cycling tests at 1150 degrees C. After oxidation and thermal cycling tests, formation of thermally grown oxide (TGO) layers at the interface and crack surfaces were investigated according to analysis results. The results show that double layered TBC system exhibits better oxidation performance in terms of TGO growth and thermal cyclic lifetime compared to single layer TBC system.