Boron Carbide Coatings for Enhanced Performance of Radio-Frequency Antennas in Magnetic Fusion Devices

Dense, adherent, and thermally conductive boron carbide coatings are needed to protect radio-frequency components used to heat the plasma for magnetic fusion energy. However, the only source of dense enough coatings is a physical vapor deposition process that is slow and costly. The cathodic (vacuum) arc would be a candidate coating technology that is capable of high deposition rates at a lower cost. Unfortunately, its application to boron-based coatings is limited due to poor electrical conductivity and thermal stress tolerance of boron-based cathodes. This project will use properly sintered cathodes and in situ heating of the cathode in order to overcome not only the poor conductivity but also the thermal stress problem. In Phase I, it was shown that while hot-pressed or simply-pressed boron and poron/carbon cathodes collapse under the thermal stress of the arc, specially sintered boron carbide cathodes resisted thermal stress. This result was verified independently in both a continuous arc and a pulsed arc. In Phase II, advanced technology will be applied to a specially sintered cathode for continuous, uniform heating. A sintered material with a higher boron-to-carbon ratio will be produced (up to almost pure B), since the coatings obtained during Phase I were too carbon-rich. Improved substrate heating and biasing will be pursued to further encourage the desired crystal growth with dual boron and carbon sources. Commercia! Applications and Other Benefits as described by the awardee: An economically viable coating technology would not only be important for magnetic fusion energy, but also for important industrial applications in extending the wear life of cutting tools, gears, bearings and numerous automotive components