Tribological And Wear Properties Of 304 Austenitic Stainless Steel Nitrided By Low-temperature Radio Frequency Plasma

Austenitic stainless steels are widely used in petroleum, chemical, pharmaceutical, food and other industries for their excellent corrosion resistance, but low hardness (only about HV260) and poor resistance to wear lead to a short lifetime in industrial applications with. Up to now, people have been seeking ways to improve its hardness and wear resistance. Nitriding, which is an effective technique for strengthening the surface of materials to improve their surface hardness, tribological and corrosion properties, has been developed for many years. However, for austenitic stainless steels at high temperature, the nitrided layer formed is accompanied by CrN precipitation, resulting in a significant decrease in corrosion resistance. On this paper, low-temperature plasma nitriding can improve the hardness and wear resistance of austenitic stainless steels without losing corrosion resistance by producing a metastable phase supersaturating nitrogen atoms which is usually called expanded austenite Y n or S-phase. So; the corrosion resistance of austenitic stainless steels can be remained or improved while the surface hardness and wear resistance are obviously increased.Combined with the current research status, people tend to focus on the relationship between quality of the film and discharge of the macroscopic parameters, such as gas pressure, discharge voltage, discharge current, discharge frequency, and ignore the microscopic parameters of the plasma, such as ion density, ion temperature, electron density, electron temperature, etc. In this study, the research was focused on the observation of the changes induced in the surface of sample after plasma nitriding process and the resulting surface properties the influence of nitriding from the point of view of energy and ion current density. In order to achieve the purpose of stainless steel surface modification, the paper mainly studied the effect of ion current density on bias, working pressure, hardness and friction coefficient. The phase composition, surface hardness and tribological properties of the nitrided and untreated AISI304 austenitic stainless steel were studied by X-ray diffraction (XRD), microhardness tester and ball-on-disc tribometer. Optical emission spectroscopy (OES) was used to investigate the active species present during rf plasma nitriding.Through many experiments, the optimal technology is founded out. When the nitrogen flow is lOsccm, radio frequency power is 80W, the working pressure is 10Pa, the bias voltage is-500V and the nitriding time is 2h, the nitrided layer has the best properties. In this condition, the surface of the nitriding layer has small and uniform particles. The hardness is up to 850HV0.025, the surface wear resistance is increased. As the ion beam current density increases, the effect of nitrogen is better. Optical emission spectroscopy is used to monitor glow plasma particle. And N2* and N2+ play an important role during the rf plasma nitriding.