Research On The Characteristics Of Low-power, High-Efficiency Plasma Spraying

Thermal plasma spraying is one of the important technologies in modern surface engineering. Thermal plasma spraying can obtain the coatings of high quality for its superior characteristics of high-temperature and high-velocity. Generally, in the traditional plasma spraying, the powders were injected into the plasma jet from outside the nozzle. So the power consumption is large, but the powder deposite rate is low. Prof. Gao Yang in Dalian Maritime university has developed an innovative low-power, high-efficiency, and inner-powder-feed plasma spraying which has lower power consumption and higher deposite rate.In this paper, the enthalpy probe was adopted to measure the temperature and velocity of low-power plasma jet outside the nozzle for analyzing the influence of gas composition and gas flow rate on the plasma characteristics of arc voltage, temperature, velocity and heat-transferring. The coatings formed in the different spraying conditions were also investigated for researching the influences of gas composition on the qualities of coatings. In addition, the accelerating and heating of the particle in plasma jet was studied by numerical simulation. The conclusions are stated as below:1. In Ar plasma spraying, when a new nozzle was used, increasing the gas flow rate of Ar will enhance the arc voltage, temperature and velocity of plasma jet. In Ar-Hi and Ar-N2 plasma spraying, augmenting the H2 or N2 content in plasma gas will also increasing the arc voltage, and the heat-transfer ability of plasma jet. Ar-Hb plasma jet has the highest heat-transfer power to the probe for the high thermal conductivity ofH2.2. In low-power plasma spraying, the gas composition remarkbly affect the qualities of coatings. The coatings created by Ar-H2 plasma spraying are suprior to those formed by Ar-N2 plasma spraying.3. The accelerating of powder is determined by the density and the diameter of powder. The effect of latter is more notable. The heating of powder in plasma jet is affectedby the diameter, density, specific heat and the melting point of the powder.