Resistance of microcrystalline and nanocrystalline Cu/Cr pseudo-alloys to vacuum discharge

Microcrystalline and nanocrystalline Cu/Cr pseudo-alloy electrodes were prepared from elemental powders using high-energy ball milling and spark plasma sintering, and were characterized by SEM, TEM, EDS, and AFM. Vacuum discharge tests were conducted in order to reveal how the microstructure influences the material resistance to surface damage by vacuum electric sparks and arcs. Numerous micro-craters with morphologies typical for explosive electron emission appeared on the surface of the microcrystalline cathode, while the surface of nanocrystalline cathode remained undamaged. At the same time, vacuum discharge caused Cu to melt on the anode surface for both types of microstructure, and vacuum arc melts Cu and Cr independent of the microstructure and electrode polarity. Thus, a decrease of the Cr grain size may prevent cathode material damage by explosive electron emission (probably due to electron scattering on the grain boundaries), and only slightly influences the resistance of electrodes against arcing or high-energy electron bombardment. These results can be used in development of new electrodes for vacuum interrupters, cathodes of vacuum diodes and other equipment that involve vacuum discharges.