Creation of Highly Dense Ceramic Films by Using Magneto-Plasma Dynamic Arc Jets

在磁等离子体动力学（MPD）电弧发生器中，等离子体被电磁力加速。与传统的热等离子体炬相比，MPD电弧发生器可以产生更高速度、更高温度、更高密度和更大面积的等离子体。针对MPD电弧发生器在陶瓷涂层中的应用，研制了两种类型的MPD电弧发生器。一个是用莫来石或氧化锆陶瓷覆盖的阴极，另一个是钛阴极。前者用于莫来石或氧化锆涂层，因为阴极盖有烧蚀过程；后者用于氮化钛活性涂层，用氮气。对涂层特性进行了评价；通过等离子体诊断测量和流场分析，了解等离子体特征和等离子体加速过程，阐明涂层特性与等离子体流动特性之间的关系。涂层性能评价表明，MPD电弧发生器具有很高的陶瓷喷涂潜力。在氮化钛反应涂层中，期望从MPD发生器中高速排出大量的N和N^+。与传统的低压热喷涂相比，在衬底位置保持较高的电子温度和电子数密度。具有N^+， Ti， Ti^+和Ti^<2+>的激发粒子的化学活性等离子体有望促进更好的氮化钛涂层。

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. The MPD arcjet generator can produce higher-velocity, higher-temperature, higher-density and larger-area plasmas than those of conventional thermal plasma torches. For applications of MPD arcjet generators to ceramic coatings, two types of MPD arcjet generators were developed. One was provided with a cathode covered with Mullite or Zirconia ceramics and the other with a titanium cathode. The former was operated with Ar for Mullite or Zirconia coating due to ablation process of the cathode cover and the latter with N_2 for titanium nitride reactive coating. The coating characteristics were evaluated; plasma diagnostic measurement and flowfield analysis were also conducted to understand plasma features and plasma acceleration processes and to clarify relationships between the coating characteristics and the plasma flow characteristics. The coating characteristics evaluated showed that the MPD arcjet generators had high potentials for ceramic spray coatings. In the titanium nitride reactive coating, a large amount of N and N^+ was expected to be exhausted with a high velocity from the MPD generator. Both the electron temperature and the electron number density were kept high at a substrate position compared with those for conventional low-pressure thermal sprayings. A chemically active plasma with excited particles of N^+, Ti, Ti^+ and Ti^<2+> were expected to contribute to better titanium nitride coatings.