Наука и техника (May 2018)
CALCULATION OF PARTICLES FLOW TEMPERATURE DURING PLASMA SPRAYING OF MIXTURE CONSISTING OF SELF-FLUXING POWDER AND CERAMICS
Abstract
Plasma spraying is one of the most effective methods allowing both to restore worn surfaces of parts and create wearresistant coatings on new parts aiming the increase of their service life. Properties of the produced coatings depend on number of parameters, such as a plasma temperature, a chemical and fractional composition of the sprayed mixture, a distance from a plasma torch to the surface of a part, etc. Mathematical modeling of the process can significantly reduce the cost of processing of technological modes and is widely used at present for a calculation of technological parameters. The paper is devoted to mathematical simulation aiming to determine an effect of the injected ceramics content on the change in a temperature of a particles flow, as well as finding the modes in which the particles of high-temperature ceramics will be in the liquid state when they are deposited on the surface of a product. A mathematical model of particles heating in plasma has been formulated and a system of equations has been compiled. The system of equations has been solved numerically in Mathcad by a standard procedure using the Rkadapt function. Calculations have been carried out for a volume concentration of Al2O3 ceramics in a mixture from 5 to 50 % and for a plasma temperature at the exit from the plasma torch in the range from 6000 to 10000 K. Calculations have shown that the concentration of ceramics does not significantly affect the temperature of a mixture. The temperature of the particles depends to a large extent on the temperature of the plasma and the diameter of particles. It has been determined that for the entire range of calculated values the temperature of the self-fluxing powder in contact with the substrate exceeds a melting point. Fractional particle size has a strong effect on the temperature of particles at the moment of contact with the substrate. The dependences of a temperature of the ceramic phase on the particle size at different concentrations and plasma temperature have been determined. Analysis of the coatings microstructures has shown a good correlation with the results of the calculation.
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