Effect of cathode microstructure on erosion of copper cathodes - An experimental study.

摘要

The erosion of copper cathodes having different microstructures ranging from hundreds of nm to tens of mum were studied in both pulsed vacuum arcs and continuous running magnetically rotated atmospheric pressure arcs. Cathodes having different grain sizes were formed by various thermal spray and heat treatment methods namely, high-velocity oxygen fuel (HVOF) method, atmospheric pressure plasma spraying (PS), vacuum plasma spraying (VPS), cold spraying (CS) and annealing techniques.;As sprayed HVOF and CS coatings spalled severely due to their poor coating adhesion strength, as well as low electrical and thermal conductivities. However annealing these coatings in inert atmosphere improved their properties and reduced spalling. Annealing conditions, which gave minimum or no spalling of the coatings, were determined. The effect of coating initial thickness on erosion rates was also determined.;Microstructural analysis of the coated cathodes after erosion experiments show that the initial grain size of the coatings remain intact even after erosion experiments.;The coatings produced were characterized for their chemical composition, oxide content, microstructure, porosity and thermal conductivity. Arc velocity and erosion measurements were performed on these cathodes. The results show that, the cathodes having smaller grain sizes show higher arc velocities and hence give lower erosion rates. Annealed HVOF, CS coatings and as-sprayed VPS coatings which had grains sizes from 4 to 0.9 mum gave up to 60% higher arc velocities and up to 70% lower erosion rates than Cu cathodes having grains sizes from 20 to 23 mum.