High temperature corrosion resistance of silicate based nanostructured thermal barrier coatings using Al2O3–(Y2O3) ZrO2/SiO2 nanocomposite

• Silicate based structural phase ZrSiO4, Al2SiO5 and Y2SiO5 at elevated temperature
• Stabilization of t-ZrO2 phase in cyclic oxidation and hot corrosion test
• Elastic properties and microstructural analysis of TBCs

In this study, amorphous nanocomposite of Al2O3–(Y2O3) ZrO2/SiO2 was used for multilayer nanostructured thermal barrier coatings (TBCs) on SS 316L specimens. Thermal stability of the TBCs was investigated in terms of direct heat treatment, isothermal cyclic oxidation, and hot corrosion molten salt (50 V2O5 + 25 Na2SO4 + 25 NaCl) wt.% at different temperatures (800, 900 and 1000 °C) for 100 h. The X-ray diffraction patterns for the heat-treated and hot corrosion-tested specimens showed the stable structural phase composition of t-ZrO2, Al2SiO5, ZrSiO4, and Y2SiO5 with an absence of m-ZrO2. Similarly, the scanning electron microscopic images showed dense and crack-free surface coating with a random porosity. However, the molten salt-deposited specimen at 1000 °C showed the surface deformation with cracks and patches. In addition, Brunauer–Emmett–Teller surface area and pore size distribution values of TBCs were in the range of 634–493 m2g− 1 and 2.64–2.49 nm, respectively. The rate of TBC oxidation was found to increase with an increase in temperature and resulted in a cyclic oxidation which has higher oxidation resistance those of hot corrosion. The elastic properties of TBCs were investigated by nanoindentation technique where average hardness (H) and elastic modulus (Er) were in the range of 16.36 ± 0.03 to 21.67 ± 0.02 GPa and 70.01 ± 0.07 to 62.87 ± 0.09 GPa, respectively, whereas the same for molten salt-tested specimen, it was decreased in their range from 14.88 ± 0.12 to 14.04 ± 0.29 GPa and 75.81 ± 0.30 to 92.80 ± 0.21 GPa, respectively.