The direct-current arc plasma jet generator is a promising plasma device suitable for economically assisting material processing in which a high throughput of material is desired. In this paper, spectroscopic and electrostatic probe measurements are made to examine plasma characteristics near a titanium substrate plate under nitriding for a direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from plasma are also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen are used as the working gas. The relationships between the plasma and heat flux characteristics and the substrate nitriding characteristics are discussed. Paper includes a German-language abstract.