Study on particle characteristics and microstructure of La₂Ce₂O₇ coating by atmospheric plasma spraying based on the response surface method

Based on the Box-Behnken response surface method, the regression experiments for the three factors of atmospheric plasma spraying (arc current, argon flow rate, and hydrogen flow rate) were designed by Design Expert software. The velocity and temperature of La₂Ce₂O₇ particles were monitored by SprayWatch-2i on-line diagnosis system. By the statistic analysis, the regression models of particle temperature and velocity were established. Scanning electron microscope (SEM) was used to characterize the coating microstructure. The area fraction of non-molten particles and porosity were calculated by Image-Pro-Plus software. The results show that, the La₂Ce₂O₇ particle velocity is well fitted by the linearity regression model. The current and argon flow rate are the main parameters influencing the particle velocity. The particle velocity increases linearly with the increase of argon flow rate and current. The maximum velocity of particles can be obtained at the argon flow rate of 120 L·min^-1, the current of 600 A, and the hydrogen flow rate of 10 L·min^-1. However, the particle temperature conforms to the quadratic regression model, which is strongly influenced by the argon flow rate, the current, and the interaction between the current and argon flow rate. The maximum velocity of particles can be reached at the argon flow rate of 74.22 L·min^-1, the current of 543.96 A, and the hydrogen flow rate of 10 L·min^-1. The melting state of the particles increases and the non-molten particles decrease in the La₂Ce₂O₇ coating.