Effect of Dy2O3 doping on phase compositions, microstructures, thermophysical properties and fracture toughness of YSZ coatings

Yttria-stabilized zirconia (YSZ) coatings with different Dy2O3 doping contents were prepared via plasma spraying. The effects of phase compositions, microstructures and lattice defects on the thermal conductivity, fracture toughness and thermal shock resistance were analyzed. The result indicates that the Dy2O3 doping significantly affects thermophysical properties of YSZ coatings. The Dy2O3 doping can improve the insulation performance of the YSZ coating and the minimum thermal conductivity of the coating has reached 0.89 W/K·m. A decrease in thermal conductivity with increasing Dy2O3 doping content can be attributed to the lattice distortion, ions substitution, oxygen vacancies and reducing grain size. Meanwhile, the Dy2O3 doping causes the fracture toughness of YSZ coatings to decrease. Consequently, the Dy2O3-doped YSZ coatings exhibit weaker thermal shock resistance because the Dy2O3 doping promotes the formation of the cubic YSZ phase. The tetragonal phase in plasma-sprayed coatings is beneficial for service lifetime owing to its phase transformation and ferroelasticity-induced toughening under stress. Although the Dy2O3-doped YSZ coatings undergo more severe sintering owing to a decrease in the activation energy of grain growth caused by lattice distortion, they exhibit better phase stability than the YSZ coating under high temperatures because the Dy2O3 doping inhibits the diffusion of Y. Finally, a Dy2O3-doped ZrO2 coating composed mainly of the tetragonal ZrO2 phase was designed, which exhibited a better thermal shock resistance.