Abstract

Plasma spraying is gradually becoming an important technique in the material processing field, if it would give additional value to the process by allowing the area and the thickness of the deposited film to be controlled. Plasma sources for heating and accelerating the high melting point (HMP) ceramic particles have been produced untiI now in a continuous D.C. plasma mode[l], [21 However, we would like to propose the application of a pulsed plasma produced with extremely large currents of tens of kA to plasma spraying. Our experiments were conducted with a specially developed plasma torch with a pulsed discharge current with a 24 kA peak and a 400 micro-second duration. The pulsed discharge current was provided by a capacitor bank with a maximum energy of 14 kJ. The simultaneous, in-fIight measurements[3] of particle temperature, velocity and size was carried out for alumina particles injected into the pulsed plasma. The results that we have obtained, showed that the surface temperature of the alumina particles reached 2,700 to 3,300 K which was considerably higher than the melting point of alumina. Particle velocity was found to be around 200 m/s which is comparable to particle velocity in the D.C. plasma mode. The details of the coating formed on the substrate with one shot of pulsed plasma were investigated with Scanning Electro-Microscopy(SEM). The experimental results have confirmed the applicability of pulsed plasma to the spraying of refractory materials.

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