Mechanical Properties and Thermal Shock Resistance of 8YSZ-Al2O3 Composite Coatings with Different Thicknesses

Abstract

The mechanical properties and thermal shock resistance of plasma-sprayed 8YSZ-Al2O3 composite coatings with different thicknesses have been analyzed. At a thickness of 330 μm, the Young’s modulus of the coating surface increased from 96.54 to 121.39 GPa and the surface hardness from 6.63 to 9.14 GPa when the Al2O3 content was varied from 10 to 40 wt.%. Adding more alumina in the coating resulted in a change in the coating surface residual stress from tensile (48.8 MPa) to compressive (−115.9 MPa), while the thermal shock resistance at 1100 °C decreased from 162 to 56 cycles. Moreover, at given Al2O3 content, the thermal shock resistance of the coating decreased drastically when its thickness was increased, which can be attributed to the enhanced Young’s modulus and hardness near the bond coat/ceramic coating interface. An increase in the ceramic thickness resulted in a significant stress gradient as well as strain energy in the direction of the coating thickness, bringing about high thermal stress during thermal shock testing. The horizontal crack propagation caused by thermal stress in the interface area could be the main reason for coating failure.