Investigation of particle characteristics, composition and microstructure of LaxCe1 − xO2 − x/2 thermal barrier coatings during supersonic atmospheric plasma spray using Box–Behnken design

• BBD method was introduced to optimize the spray parameters.
• Establish the relationship between particles in-flight behavior and spray parameters
• Ce4+ content decreased with increasing the particle temperature.
• Microstructure of LC coating can be tailored by particles temperature and velocity.

In this work, Box–Behnken design was used for investigating the influence of the main operating parameters (Argon flow rate: Ar, hydrogen flow rate: H2 and arc current: I) on velocity and temperature of La2Ce2O7 in-flight particle characteristics (i.e., mean velocity and temperature) during supersonic atmospheric plasma spraying (SAPS). The relationship between the particle characteristics and the composition and the microstructure of LC coating was investigated eventually. During spraying, the particle temperature and velocity were monitored by on-line diagnosis system. The results indicated that the particle velocity linearly increased with the increase of Ar, H2 and I. I and the interaction between I and Ar and/or H2 were the most important parameters which influenced the particle temperature. The content of Ce4 + in the as-sprayed coating rapidly decreased when the particle temperature increased from 2923 to 3036 °C, and then slowly decreased in the range of 3127–3218 °C. When the particle velocity fluctuation was less than 5%, the porosity of as-sprayed coatings decreased with the increase of particle temperature, however, it increased with the increase of particle velocity.