Advantages of Supersonic Plasma Spraying Process

       The quality of the plasma sprayed layer is greatly affected by the particle properties, speed, and temperature melting degree. Compared with ordinary plasma spraying, the outstanding advantage of supersonic plasma spraying is the high speed of the jet. Due to the high speed, the residence time of the sprayed powder particles in the jet is shortened, the momentum of the molten or semi-molten particles hitting the substrate increases, the energy conversion efficiency is high, the droplet spreads fully, the flatness is good, the coating is dense, and the porosity is low. Bond strength The overall indicators such as the toughness of the coating have been improved, and the characteristics of supersonic plasma spraying are as follows.



(1) The jet has high enthalpy, high speed and stable concentration.



Supersonic plasma spraying not only has the characteristics of high temperature and high enthalpy of plasma spraying, but also has the characteristics of high speed of supersonic flame spraying. The characteristics of high temperature, high enthalpy and high speed make the coating quality better than that of ordinary plasma spraying coatings. The range of sprayable materials is wider than that of supersonic flame spraying materials. The spraying of some materials is similar to low-pressure plasma spraying, which overcomes the divergence of plasma jets. Disturbance and poor acceleration of sprayed particles, while the size of the sprayed part is not limited by the vacuum chamber.



The plasma jet is efficiently compressed and remains stable even away from the nozzle. For example, when spraying WC-Co powder, the slender plasma beam has not diverged for up to 1m.



(2) The arc voltage is high (up to 220V), which meets the requirements of the high-voltage, low-current operation scheme.



(3) The plasma jet is fully compressed, the beam is long and concentrated, and the energy density is high. The length of the plasma jet outside the nozzle is 2 to 3 times that of conventional plasma spraying.



(4) Due to the improved heat transfer efficiency of the flame flow to the sprayed particles, especially the increase of the kinetic energy of the sprayed particles, the coating quality is obviously better than that of conventional plasma spraying, and is similar to explosive spraying and supersonic flame spraying.



(5) The spraying material (especially the metal phase in metal-ceramic composite or gradient coating) has a short time in the high temperature jet, which overcomes the shortcomings of oxidation and burning of powder particles, and forms pollution and inclusions after coating. Defects are significantly reduced.



(6) The flying speed of the sprayed particles is high (about 400m/s ~ 600m/s, and the ordinary plasma spraying is about 200m/s ~ 300m/s), forming a dense lamellar structure of the coating, and the bonding strength between the lamellae (cohesive strength). ) and coating-substrate interface bond strength (macro bond strength) were improved.



(7) The porosity of the coating is greatly reduced, generally less than 1%, especially the lamellar structure is fully deformed and dense, which overcomes the appearance of open pores (or through holes) and effectively slows down the oxidation of alloy components in the coating. .