Abstract
Inferior fracture toughness (KIC), low thermal expansion coefficient (CTE), thermochemical incompatibility with bond coat and growth of thermally grown oxide (TGO) are the main destruction factors in conventional Gd2Zr2O7 (GZO) thermal barrier coating (TBC) undergoing thermal cycling. In this paper, to overcome these drawbacks, nanostructured GZO and an intermediate conventional YSZ layer between top and bond coats were used in the TBC system. Single-layer nanostructured GZO and dual-layer YSZ/nanostructured GZO coatings were deposited with atmospheric plasma spray technique on Ni-based superalloy (IN738LC) substrates as a topcoat with a CoNiCrAlY bond coat. Oxidation behaviour of samples was studied and compared in the cyclic mode at 1100 °C for 4 h in each cycle. Also, CTE and KIC of the nanostructured GZO and intermediate YSZ layers were investigated. The results indicated that the oxidation life of dual-layer YSZ/nanostructured GZO coating was 3.2 times more than that of single-layer nanostructured GZO. The microstructural analysis indicated that the growth rate of TGO was considerably slower for dual-layer coating due to reduced oxygen infiltration and cracks propagation. Also, nanostructured topcoat improved the thermochemical compatibility and mechanical properties in TBCs.
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