Phase transformation and thermal conductivity of the APS Y2O3 doped HfO2 coating with hybrid structure

Abstract

Hafnia-based materials are very promising to serve as thermal protecting coatings at temperature above 1200 °C. In this work, two kinds of 8 mol% Y2O3 stabilized HfO2 ceramic coatings (YSH-SN and YSH-MX) with conventional and hybrid structures were prepared by air plasma spray (APS) method. The microstructure, thermal conductivity and the mechanical properties of the coatings before and after thermal exposure at 1300 °C were compared in detail. Results show that the as-sprayed YSH-MX has a hybrid laminated structure of monoclinic HfO2 and cubicY2O3 splats, and transforms to monoclinic HfO2 and cubic YSH after thermal exposure, while the YSH-SN is composed of major tetragonal YSH phase and transforms to monoclinic HfO2 and cubic YSH afterward. Thermal conductivities at ultra-high temperature (1600 °C) before and after thermal exposure for those two coatings are close, and the fracture toughness in the direction parallel to the interface exceeds 2.1 MPa m0.5. The YSH-MX coating with a hybrid structure provides insights to conveniently prepare gradient coating or other coatings with complex structures.