Anode erosion during pulsed arcing

An experimental study of the anode erosion rates of Cu, Zr, Ti, Mo, Ta, and W is presented under conditions similar to those used for electrodischarge coating. The arcs are conducted between a small anode and a larger cathode in air with pressures ranging from 10/sup -4/ to 10/sup 3/ torr. Unipolar arc pulses of 200-400-A peak current and 0.1-ms duration are produced at a 100-Hz pulse repetition rate by an RC circuit. For most materials, the electrode mass loss is primarily from the anode, and the mass loss is independent of pressure for pressures less than 0.1 torr, decreases steeply with increasing pressures in the range 0.1 to 10 torr, and decreases more gradually with increasing pressure above 10 torr. The experimental results are explained by using a limiting case of the integral conservation laws. In the low-pressure region the input energy is expended mainly in the acceleration of the metal vapor, and thus the erosion rate is independent of pressure. In the intermediate-pressure region the metal vapor jet is braked by its interaction with the surrounding gas. In the high-pressure region the vapor jet is completely halted, and vapor transport takes place only by diffusion through the surrounding gas.<
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