Effect of Nitriding Time on the Structural Evolution and Properties of Austenitic Stainless Steel Nitrided Using High Power Pulsed DC Glow Discharge Ar/N2 Plasma

Abstract

A high power pulsed DC glow discharge plasma (HPPGDP) system was employed to perform fast nitriding of AISI 316 austenitic stainless steel in Ar and N2 atmosphere. In-situ optical emission spectroscopy and Infrared pyrometer measurements were used during the plasma nitriding to investigate the effect of dynamic plasma on the nitriding behaviour. SEM and EDX, XRD, Knoop indentation, and tribo-tests were used to characterize microstructures and properties of the nitrided austenitic stainless steel samples.HPPGDP produced high ionization of both Ar and N2in the plasma that corresponded to dense ion bombardment on the biases steel samples to induce effective plasma surface heating and to form high nitrogen concentration on the biased steel surfaces, and therefore fast nitriding (> 10µm/hour) was achieved. Various phases were identified on the nitrided stainless steel samples formed from a predominantly a single phase of nitrogen supersaturated austenite toa multi-phase structure comprising chromium nitride, iron nitride and ferrite dependent on the nitriding time. All the nitrided AISI 316 austenitic stainless steel samples were evaluated with high hardness (up to 17.3 GPa) and exceptional wear resistance sliding to against hardened steel balls and tungsten carbide balls.

Low Temperature Nitriding of Metal Alloys for Surface Mechanical Performance

“…Although atmospheric pressure plasma techniques have been developed during the last decade [ 11 ], most of them use low-pressure plasmas [ 12 ]. The main technologies are the pulsed DC plasma [ 13 ], Radio Frequency driven plasmas (Inductively Coupled Plasma: ICP, Antenna generated or less common Capacitive or Surface Wave Coupling), usually working in a post-discharge mode, and microwave-based ECR (Electron Cyclotron Resonance) plasmas. Whatever the technology, the main advantage of the plasma atmosphere for surface treatments is the presence of highly reactive species: ions and radicals [ 14 ].…”