Degradation mechanism of dual-phase thermal barrier coatings Gd2Zr2O7 + 8YSZ under hot corrosion in pure Na2SO4

Abstract

The research presented in the article concerns the identification and characterisation of degradation mechanisms of two-phase coating thermal barriers based on the 8YSZ/Gd₂Zr₂O₇ (8YSZ/GZO) system, and analysed under the conditions of exposure to pure sulphate salts of the Na₂SO₄ type. The scope of the presented research included the characterisation of microstructural phenomena in conditions of heating at a temperature of 920 °C for 240 h, followed by heating at a temperature of 970 °C for another 96 h until visually significant degradation effects of the ceramic coating were achieved. Detailed studies of the phase and chemical composition using XRD and SEM/EDS methods were carried out on the surface of the tested coatings and their cross sections to describe microstructural phenomena. The analysis of the phase composition of the ceramic layer showed the course of degradation processes based on the disintegration of the pyrochlore phase into intermediate forms of non-stoichiometric fluorite with the simultaneous enrichment of tetragonal zirconium oxide into a cubic form with a high content of the stabilising phase (Gd₂O₃). Tests on model powder systems confirmed the degradation mechanism of two-phase TBC coatings.