AVS 65th International Symposium & Exhibition
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuP

Paper PS-TuP30
Plasma Nitriding of Highly Polished Metallic Surfaces

Tuesday, October 23, 2018, 6:30 pm, Room Hall B

Session: Plasma Science and Technology Division Poster Session
Presenter: Yoshiki Handa, Meijo University, Japan
Authors: Y. Handa, Meijo University, Japan
P. Abraha, Meijo University, Japan
Correspondent: Click to Email
This research presents an appropriate plasma nitriding method for highly polished precision metallic components that need to maintain the as-finished surface conditions after the plasma treatment. Conventionally, a nitrided layer consists of a hard but brittle nitrogen compound layer and a layer made of diffused interstitial nitrogen atoms. The compound layers, Fe3-2N (gamma-prime) and Fe4N (epsilon) form when the phase field has a solubility range of about 6-8 percent weight nitrogen. A high concentration of the nitrogen atoms on the surface, or concentration gradient, drives the atoms along the grain boundaries of the sample to form the diffusion layer. In this research, the incidence of the electrically charged electrons and ions is controlled to suppress the formation of the gamma-prime and epsilon phase fields and maintain a steady flow of interstitial nitrogen atoms along the subsurface. In this configuration, the sample is set inside a shielding grid that is located in the electron beam excited plasma chamber. The shielding grid is a 40-mesh screen biased negatively, while the sample is biased positively. The negatively biased grid repels the electrons that cause overheating in addition to attracting the ions for possible charge exchange with the meshed wire, thus increasing the atom density. On the other hand, the sample is positively biased to avoid any incoming ions from approaching the sample. In this experiment, the driving parameters of the built-in bias configuration were optimized to guarantee a diffusion-based nitriding that suppresses the formation of the compound layer. A comparison is then made based on measurements of the plasma species that interact with the samples and the characteristics of the treated samples in using both the diffusion-based method, neutral nitriding, and the conventional ion nitriding method. The results show neutral nitriding is a successful nitriding method that can strengthen the surface while keeping the surface free of the compound layer.