Performance of TBCs system due to the different thicknesses of top ceramic layer

Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) with thicknesses of 200μm and 400μm were sprayed using supersonic plasma spraying (SPS) on FeNi-based substrate and Ni-based substrate, respectively. Bonding strengths of FeNi-based substrate and Ni-based substrate with different thicknesses of coatings were investigated. Bonding strength tests revealed different fracture mechanisms for the specimens with thin topcoat and thick topcoat. Scanning electron microscope (SEM) and metallographic microscope observation of the crossing sections revealed that the porosity of the thin coating was smaller than that of the thick coating, and the distribution of the porosity further determines the location of the fracture zones. Thermally grown oxide (TGO) with different thicknesses grows on the interface of the bond coat (BC) and top ceramic layer due to oxidation. Analysis validates that thickness of the topcoat plays an important role in the diffusion of oxygen and oxidation rate of the TGO while the porosity has little effect on the oxidation rate.