Structure and thermal conductivity of yttria-stabilized hafnia ceramic coatings grown on nickel-based alloy

Yttria-stabilized hafnia (YSH) coatings were produced by sputter-deposition onto nickel (Ni) based super alloy substrates. The deposition was made by varying the growth temperature from room-temperature (RT) to 500 °C. The microstructure and thermal properties of the YSH coatings were evaluated employing grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and phot-acoustic measurements. GIXRD studies indicate that the coatings grown at RT are amorphous while those grown at 300 °C and higher are crystalline. The crystalline YSH coatings crystallize in cubic hafnia phase and exhibit slightly enhanced lattice parameter compared to pure hafnia. The average grain size increases with increasing growth temperature. Thermal measurements indicate an effective reduction in thermal conductivity of YSH coatings compared to pure hafnia.