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 characterise microstructures and properties of the nitrided austenitic stainless steel samples. HPPGDP produced high ionization of both Ar and N2 in the plasma that corresponded to dense ion bombardment on the biased 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 to a 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 sliding wear resistance against hardened steel balls and tungsten carbide balls.
Highlights
Pulsed glow discharge plasma techniques have been extensively studied in the past decades for surface coating [1,2], plasma nitriding [3,4], combination duplex treatment of nitriding plus coating [5,6] and plasma ion implantation [7,8]
This paper reports the structure and properties of nitrided austenitic stainless steel AISI 316 as influenced by the nitriding time and the process temperature
The optical emission spectra were detected from the titanium surface during high power pulsed DC glow discharge plasma (HPPGDP) process in which the glow discharge plasma was started with pure Ar at a pressure of 1.33 Pa and with power increased from 1.0kW to 4.5kW
Summary
Pulsed glow discharge plasma techniques have been extensively studied in the past decades for surface coating [1,2], plasma nitriding [3,4], combination duplex treatment of nitriding plus coating [5,6] and plasma ion implantation [7,8]. Energetic particles have several effective uses, such as ionetching, ion-cleaning, ion-implantation, and ion-enhanced coating deposition [11,12,13] These can be exploited to ensure the treated surfaces have specific properties and microstructures. If sufficient atom diffusion mobility is provided at a relatively high process temperature, the nitrided layer comprises a multi-phase structure of chromium nitride (CrN and/or Cr2N), iron nitride, and the metallic ferrite phase [28,29,30]. Plasma nitriding treatments of austenitic stainless steels bring about pronounced structural changes and show great impact on the surface properties. This paper reports the structure and properties of nitrided austenitic stainless steel AISI 316 as influenced by the nitriding time and the process temperature. An initial tribological investigation of the resulting nitrided stainless steel surfaces is reported
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