Effect of Isothermal Oxidation on Adhesion Strength for Typical Ysz and Rare-earth Lzo Thermal Barrier Coating

Investigation on the effect of Thermally Grown Oxides (TGO) on the adhesion strength for thermal barrier coating (TBC) was carried out. The TBC under studied was the multilayer systems which consist of NiCrAlY bond coat and YSZ/LZO ceramic coating deposited on Ni-based superalloy substrates. The development of Thermally Grown Oxides (TGO) for both TBC systems after isothermal oxidation was measured. Isothermal oxidation was carried out at 1100 °C for 100 hours to age the samples. ASTM D4541: Standard Test Method for Pull-off Strength of Coatings using Portable Adhesion Tester was used to measure the adhesion strength of both TBC systems before and being aged. The effect of the developed TGO on the measured adhesion strength was examined and correlation between them was established individually for both TBC systems. The failure mechanism of the both system was also has been identified; either cohesive or adhesive or the combination of both. The results showed that TGO has been growth more than 50 % from the bond coat layer for rare-earth LZO system compared to the typical YSZ system, which less than 10 % from the bond coat layer. This leads to the lower adhesion strength of rare-earth LZO coating system compared to typical YSZ system. Failure mechanism during the ASTM test also was found different for both TBC systems. The typical YSZ system experienced cohesive failure whereas the rare-earth LZO system experienced the combination of cohesive and adhesive failure