H. Tahara, Osaka University, Toyonaka, Osaka, Japan; Y. Ando, Ashikaga Institute of Technology, Ashikaga, Tochigi, Japan
In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive spraying was carried out using an MPD arcjet generator with crystal silicon rods and nitrogen gas. Because higher-velocity, higher-temperature and higher-density and larger-area plasmas are produced with the MPD arcjet generator than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform β-Si3N4 coating 30 μm thick was formed after 200 shots at a repetitive frequency of 0.03 Hz with a discharge current of 9 kA and a substrate temperature of 700 °C. The Vickers hardness reached about 1300. It was found that the coating thickness was highly sensitive to discharge current and that the microstructure of coating was sensitive to substrate temperature. Aluminum nitride sprayings were also conducted. A dense and uniform AlN coating 40 μm thick was formed after 50 shots with a discharge current of 10 kA and a substrate temperature of 400 °C, and the content was evaluated to be about 79 %. All results showed that the MPD arcjet generator had high potentials for spraying.
Summary: In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive spraying was carried out using an MPD arcjet generator. Because higher-velocity, higher-temperature and higher-density and larger-area plasmas are produced with the MPD arcjet generator than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform â-Si3N4 coating 30 ìm thick was formed after 200 shots. The Vickers hardness reached about 1300. Aluminum nitride sprayings were also conducted. A dense and uniform AlN coating 40 ìm thick was formed after 50 shots, and the content was evaluated to be about 79 %. All results showed that the MPD arcjet generator had high potentials for spraying.
