Structure evolution and thermal conductivity of lanthanum zirconate coating after high temperature exposure

Abstract

La2Zr2O7 powders were synthesized by solid-state reaction method. After spray granulation, the La2Zr2O7 coatings were fabricated by air plasma spray technique. The effect of heat treatment time on the properties of La2Zr2O7 coatings was investigated, focusing on phase composition, microstructure evolution and thermal conductivity. The results show that a single pyrochlore phase of La2Zr2O7 coating has been successfully fabricated. And the average porosity is 11.3%. The phase composition and porosity do not change with the prolongation of heat treatment time. The thermal conductivity of the as-sprayed coating can be as low as 0.392 W?m–1?K–1. A number of amorphous structures exist in the as-sprayed coating, which can effectively block the transmission of phonons. With an increase of thermal exposure time at 1300 ℃ in air, the amorphous structure is gradually transformed into crystalline structure, and the phonon transfer efficiency is obviously improved, resulting in a significant increase in the thermal conductivity of the coating. Interestingly, after heat treatment, the rebound effect of thermal conductivity at high temperature didn’t appear in this research.

Keywords

• TBCs
• air plasma spray
• thermal conductivity
• La₂Zr₂O₇
• heat treatment