Effect of high temperature on the surface morphology and mechanical properties of nanostructured Al2O3-ZrO2/SiO2 thermal barrier coatings

Nanostructured Al2O3-ZrO2/SiO2 multilayer coating was applied on 316L SS specimens using dip-coating method. Then, the coated specimens on heat treatment to 800, 900, and 1000 °C for 100 h showed the formation of a stable structural phase of t-ZrO2-toughened Al2SiO5 along with ZrSiO4. The microstructural images of the heat-treated specimens observed the level of porosity and that of BHJ-pore size distribution was decreased in the coating along with crack splats. Then, the coating was subjected to cyclic oxidation and hot corrosion test for 20 cycles. The obtained results showed that the rate of cyclic oxidation resistance enhanced when compared to that of hot corrosion resistance. The results of X-ray diffraction analysis showed hot corrosion resistance in molten salt, with non-leaching t-ZrO2 structural phase of ceramic coating. The mechanical properties of the nanostructured coating improved with an increase in the heat treatment. The maximum hardness (H) and reduced elastic modulus (Er) values of the coating were approximately 18.43 ± 0.62 and 68.30 ± 1.35 GPa, respectively. Spallation and oxidation resistance of the coating were explored through mechanical properties, in situ scanning probe microscopy, and atomic force microscopy. The results showed that silicate-based thermal barrier coating provided better protection to SS specimen from high-temperature corrosion.