Atmospheric Plasma Spraying Particles And Coating Performance Study

Atmospheric plasma spraying (APS) is a very complicated process, in which involve plasma arc heat transference and flow, the interaction between powder particles with plasma jet, and also involve the interaction between molten particle and substrate. Consequently, the quality of coatings is always affected by the types of plasma gun and spraying distance, and others spraying parameters. By exploring the change tendency of the particles’temperature and velocity in the spraying process, and the relationship between change tendency and the properties of coatings would be helpful to guide the APS production.In this study, F6Atmospheric plasma spraying gun equipped with cylindrical nozzle and Laval nozzle was used to generate plasma jet and deposit Al2O3-3TiO2ceramic coatings. The temperature and velocity of in flight particles were detected by SprayWatch-3i system. The morphology of individual splat was observed by scanning electron microscope (SEM). The relationship between spraying distance and coating properties such as microstructure, micro-hardness, wear property and adhesive strength was investigated. The differences between coatings which deposited by cylindrical nozzle and Laval nozzle were studied. The results obtained in this study are summarized as follows:(1) Within the measurement range, the temperature of in flight particles which were in the plasma jet that was generated by plasma gun with cylindrical nozzle, and the velocity various as the spraying distance rise firstly, decline then. The maximum value of velocity is415m/s with the spraying distance of90mm. On the other hand, in Laval nozzle conditions, the temperature increased at3300℃when the stand off distance is110mm, and the velocity various as the stand off distance rise firstly and then keep decreasing tendency. The maximal velocity is201m/s at80mm spraying distance.(2) Under the same spraying conditions, the size of splats which were obtained by cylindrical nozzle is larger than those obtained by Laval nozzle. (3) The microhardness and adhesive strength of coatings deposited by cylindrical nozzle are just a little higher than those deposited by Laval nozzle plasma gun. Moreover, the pore density is lower than the latter and the wear resistance is better than the latter.