Abstract
The conventional plasma-sprayed thermal barrier coatings (TBCs) consist of a duplex M-Cr-Al-Y bond coat and thermally insulating ZrO 2-based ceramic top coat. In this study, a new TBC system was attempted in which an intermediate Al 2O 3 layer was interposed between the Ni-22Cr-10Al-1Y bond coat and ZrO 2-8Y 2O 3 top coat (where the compositions are in approximate weight per cent) by the chemical vapour deposition (CVD) process. The performance of the triples ZrO 2-8Y 2O 3/CVD A1 2O 3/M-Cr-A1-Y TBCs was evaluated by thermal cyclic oxidation testing at 1000, 1050, 1100 and 1150°C. The phase and morphology of the Ni-22Cr-10A1-1Y bond coat pre-coated with CVD A1 2O 3, and the oxidation behaviour were analysed by X-ray diffractometry, scanning electron microscopy-electron probe microanalysis and mass gain measurements respectively, to investigate the improvement of this new system. The results of the experiments in this study showed that the TBC specimens with an oxygen diffusion barrier CVD A1 2O 3 layer on the Ni-22Cr-10A1-1Y bond coat exhibited a lower oxidation rate and generally a longer lifetime compared with the conventional TBC specimens. The transport of reacting atoms or ions in CVD A1 2O 3 might involve inward oxygen diffusion.
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