Abstract: Microscopically, plasma sprayed coating is essentially fabricated by a stream of particles which experience a series of complicated physicochemical transformations in plasma jet and undergo rapid spreading and solidification after impacting the substrate. Therefore, the deposition quality of the droplet before impinging on the substrate has an important influence on the microstructure, defect and mechanical properties of the coating. The detail process of the interaction between plasma jet and particles is introduced in four aspects, namely, the basic parameters, the mechanism of the heat, mass and momentum transfer. The results indicate that the temperature and the velocity are the basic characteristic parameters of the particles, while the synthetic parameters of the temperature and velocity are proved to be more suitable to characterize the deposition quality of the droplets; the particles are heated from surface to interior and some of the droplets are prone to vaporize due to high melting status, which are effected by thermal coefficient, specific surface area, heat capacity, injection path, jet characteristics and so on; the molten droplets is easily to react with the atmosphere, i.e. O₂, N₂ and H₂, due to high chemical activity, which can lead to the element migration and chemical reaction in the powder; the particles injected into the plasma jet are accelerated by the drag force, gravity, thermophoretic force and pressure gradient force, which can resulting in different degrees of fragmentation or refinement of the particles owing to the characteristics of the plasma jet and the molten state of the droplets.

Key words: heat and mass transfer, interaction, plasma spray, spraying particles