Influence of high-enthalpy atmospheric plasma spraying power on oxidation resistance of ZrB2-LaF3 coatings

Good oxidation resistance of ZrB2-based coatings is highly desirable for successful high-temperature applications in thermal protection systems. Herein, ZrB2-LaF3 coatings with different microstructure and morphology were prepared by high-enthalpy atmospheric plasma spraying. Particular attention was paid to the effect of spraying power on the physical properties and oxidation resistance of as-sprayed coatings. According to a thorough analysis, spraying power exerts influence on the melting degree and travelling speed of ZrB2-LaF3 agglomerates in the flame during spraying process, thus affecting the microstructure, micro-topography and porosity/density of the coatings, and conclusively, leading to the difference of oxidation resistance. The coatings produced by the lower spraying powers (35 and 55 kW) revealed poor quality and the high degree of porosity with a large number of unmolten particles. Furthermore, these underwent severe oxidation due to the diffusion of oxygen through the pores. On the other hand, the use of excessive power (95 kW) deteriorated the quality of the coating due to drastic residual stress. In turn, the moderate spraying power (75 kW) was found to be optimum for achieving the coating with desirable characteristics, namely, fully molten particles at low porosity and residual stress, being thus beneficial for improving its oxidation resistance. This discovery is therefore beneficial for the practical applications of ZrB2-LaF3 coatings.