Cyclic Oxidation Behavior of Nanostructured Double Ceramic Layer Coatings of 8YSZ/La2(Zr0.7Ce0.3)2O7 With Vertical Crack Structure

In this study, at first a precursor precipitate of La2(Zr0.7Ce0.3)2O7 was prepared by using ZrOCl2.8H2O, Ce(NO3)3.6H2O and La2O3 initial materials. The calcination process of this precipitate was performed at 400 -900 . The Phase constituents, particle size, and morphology of the calcined powders were investigated. The calcined precipitate agglomerates at 600 and 900 were used to apply by plasma spraying on the AMDRY 962 and METCO 204NS-G coated Hastelloy X substrates. The cyclic oxidation test at 1000 was done for two double ceramic layer coatings applied by agglomerates 600 and 900 and the conventional YSZ coating. According to the results of diffraction patterns and microstructural observations, the nanoparticles containing the main phases of LZ (lanthanum zirconate with low solubility of cerium cation) and LC (solid solution of cerium lanthanum zirconate) formed only in the La2(Zr0.7Ce0.3)2O7 precursor precipitate calcined at 900 because of relatively high calcination temperature. However, both double ceramic layer coatings were composed of LZ and LC phases, and theses coatings were as nano-TBCs with vertical cracks. The coating applied by agglomerates 600 had relatively less compaction compared to the coating applied by agglomerates 900 . The results of the cyclic oxidation test showed that only the coating applied by agglomerates 600 had a desirable performance. Proper microstructural compaction and the presence of vertical cracks in this coating caused this performance. Morphology of the Layers of this coating remained sound after 924 thermal cycles. While propagating crack was formed around the TGO/YSZ interface in the conventional YSZ coating after cyclic oxidation test.