An electromagnetic acceleration plasma arcjet generator, which is called Magneto-Plasma-Dynamics (MPD) arcjet generator, has a coaxial electrode structure similar to those of conventional thermal arcjet generators. However, their acceleration mechanisms are different ; that is, in MPD arcjet generator, plasma is accelerated by the electromagnetic interaction between the discharge current and the magnetic field induced by it in MW-class input power operations during the discharge, although in thermal arcjet generators the working gas is accelerated aerodynamically through a straight or convergent-divergent nozzle. As a result, the MPD arcjet generator can produce higher-velocity, higher-temperature, higher-energy-density, and larger-area plasma than those of other conventional plasma torches can. These MPD plasma properties are effective for various material processes.
This paper deals with a development of MPD arcjet generator for titanium nitride (TiN) reactive coatings. The MPD arcjet generator is equipped with a titanium cathode, and its working gas is nitrogen. The coatings were deposited onto steel substrate. The phase structure and the composition of the coatings were analyzed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their Vickers hardnesses were measured. In addition, titanium particles that were generated by MPD arcjet generator ablation process were observed by means of SEM and electron probe micro analysis (EPMA). These analyses showed that the MPD spray process could successfully form dense and uniform titanium nitride coatings. The properties of the titanium nitride coatings were highly sensitive to the titanium cathode diameter and discharge current.
