Composition, structure evolution and cyclic oxidation behavior of La2(Zr0.7Ce0.3)2O7 EB-PVD TBCs

Abstract

Lanthanum cerium zirconate (La-2(Zr0.7Ce0.3)(2)O-7, LZ7C3) as a candidate material for thermal barrier coatings (TBCs) was prepared by electron beam-physical vapor deposition (EB-PVD). The composition, structure evolution, oxidation state,surface morphology and cyclic oxidation behavior of its coating were investigated. The results from X-ray diffraction (XRD) and Raman spectra indicate that the partial decomposition of LZ7C3 ingot occurs during deposition and several weak peaks of t-ZrO2, Ce2O3 and CeO2 phases coexist in the as-deposited coating. Two new phases of La2O3 and Ce2Zr2O7 simultaneously appear for those coatings after 1 cycle. However, Ce2O3 disappears after 15 cycles. One weak Raman band is detected for all cases at similar to 600 cm(-1), which is the characteristic of Ce1-xZrxO2. From the X-ray photoelectron spectroscopy (XPS) patterns, the coexistence of La3+, Zr4+, Ce4+ and Ce3+ ions near the surface of LZ7C3 coating appears before 5 cycles. Meanwhile, the enrichment of La into zirconia and/or ceria lattices is attained with the increase of thermal cycles. The occurrence of compressive and tensile stresses, the opening up of gaps between those columnar clusters and the reduction-oxidation of cerium oxide are likely to be the primary factors for the occurrence of microcracks on the surface of LZ7C3 coating during thermal cycling. (C) 2009 Elsevier B.V. All rights reserved.