In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. TheMPD arcjet generator can produce higher-velocity, higher-temperature, higher-density and larger-area plasmasthan those of conventional thermal plasma torches. Two types of MPD arcjet generator were developed forapplications to ceramic spray coatings. One generator was installed with a cathode covered with mullite orzirconia ceramics and the other with a titanium cathode. The former was operated with Ar for mullite or zirconiacoating by an ablation process of the cathode cover and the latter with N2 for titanium nitride coating by a reactiveprocess between ablated titanium particles and nitrogen plasma. Silicon nitride reactive spraying was also carriedout. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titaniumnitride reactive spraying, plasma diagnostic measurement and flowfield analysis were conducted. A large amountof N and N+ was expected to be exhausted with a high velocity from the MPD generator. Both the electrontemperature and the electron number density were kept high at a substrate position compared with those forconventional low-pressure thermal sprayings. A chemically active plasma with excited particles of N+, Ti, Ti+ andTi2+ was considered to contribute to better titanium nitride coatings. All coating characteristics showed that theMPD arcjet generators had high potentials for ceramic spray coatings.
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