Disintegration of Composite Electroexplosive Coatings in Spark Erosion

Abstract

A mathematical model is proposed for the destruction of electroexplosive W–Cu, Mo–Cu, W‒C–Cu, Mo–C–Cu, Ti–B–Cu, and TiB2–Cu composite coatings under spark erosion associated with the opening of electrical contacts. The model describes the evaporation of the electrodes under the action of the heat flux due to sparking when the electrical contacts open. In this model, the resistance of the electrical contacts during the tests is assumed to be 40–50 μΩ. The model corresponds to the heating of a half-space by a normal pulsed surface heat source uniformly distributed over an area of specified radius, with a specified heating time. The energy distribution of the pulse over time is approximated by a rectangular pulse. The finite pulse length is taken into account in solving the heat-conduction equation in cylindrical coordinates for a plane instantaneous heat source. The vapor pressure of the metal is determined from the surface temperature. The calculations assume a contact voltage of 380 V; a current of 3 A; a spark discharge of length 150 μs; and a discharge–surface contact spot of radius 152 μm. The following parameters are determined: the surface temperature of pure electrodes; the surface temperature of the composite coatings; the depth of the evaporation layer for pure electrodes; the mass loss of the composite coating after a single discharge pulse; the relative change in bulk resistance of the pure electrodes and composite coatings to electroerosion; and the relative change in mass resistance of the pure electrodes and composite coatings to electroerosion. The content of the elements in the composite coating is determined. The model results are in good agreement with experimental data, especially for the ternary systems W–C–Cu, Mo–C–Cu, and Ti–B–Cu. The results are also in adequate agreement with literature data. For the binary systems W–Cu and Mo–Cu, the discrepancies may be attributed to the approximations made in the model.