H. Tahara, Osaka University, Toyonaka, Osaka, Japan; Y. Ando, Ashikaga Institute of Technology, Ashikaga, Tochigi, Japan
In low-pressure plasma spraying using a plasma jet generator with a supersonic expansion nozzle, the pressure and the electron density drastically decrease downstream through the nozzle, and therefore the plasma is in thermodynamical nonequilibrium state. Additionally, the supersonic expanding plasma jet is expected to be in chemical nonequilibrium state in which excited plasma particles are carried downstream in chemically-active state. Titanium nitride reactive spraying was carried out under a low-pressure environment using a DC arc plasma jet generator with a supersonic expansion nozzle. From the spectra emitted from the plasma, a reactive plasma including chemically-active titanium particles was found to be generated and irradiated on the substrate. A dense and high-quality TiN coating was formed at a low substrate temperature of 700 oC with a low input power of 5.3 kW. The Vickers hardness of the coatings increased with input power depending on nitrogen flow rate and discharge current, and it reached 2000 at 5.3 kW. The TiN concentration of the coating increased with substrate temperature, and the maximum TiN concentration of 90 % was found to be achieved at 700 oC. The results showed that the supersonic plasma jet in thermodynamical and chemical nonequilibrium state had high potentials for reactive spraying.
Summary: In low-pressure plasma spraying using a plasma jet generator with a supersonic expansion nozzle, the pressure and the electron density drastically decrease downstream through the nozzle, and therefore the plasma is in thermodynamical nonequilibrium state. Additionally, the supersonic expanding plasma jet is expected to be in chemical nonequilibrium state in which excited plasma particles are carried downstream in chemically-active state. Titanium nitride reactive spraying was carried out under a low-pressure environment using a DC arc plasma jet generator with a supersonic expansion nozzle. A dense and high-quality TiN coating was formed at a low substrate temperature of 700 oC with a low input power of 5.3 kW. The Vickers hardness of the coatings increased with input power depending on nitrogen flow rate and discharge current, and it reached 2000 at 5.3 kW. The TiN concentration of the coating increased with substrate temperature, and the maximum TiN concentration of 90 % was found to be achieved at 700 oC. The results showed that the supersonic plasma jet in thermodynamical and chemical nonequilibrium state had high potentials for reactive spraying.
