Characteristics of austenitic stainless steel nitrided in a hybrid glow discharge plasma

Abstract

A nitriding process based on two distinct nitrogen glow discharge modes, with sample temperatures ranging from 380 °Cto480°C, was employed to treat the surface of austenitic stainless steel (SS 304). The temperature is controlled exclusively by switching the operation conditions of the discharges. First mode of operation is the conventional one, named cathodic, which runs at higher pressure values (1 mbar) in comparison to the second mode, named anodic, which runs at the pressure range of 10-3 -10-2 mbar. Cathodic mode is used to quickly heat the sample holder, by the high ion flux. On the other hand, in the anodic mode, due to the lower operation pressure, higher effective ion acceleration takes place, which allows deeper ion implantation into the sample surface. This hybrid process was thoroughly explored regarding the duty cycle and conditions of operation, to achieve optimal performance of the treatments, which led to the attainment of surface hardness for samples of AISI SS 304 as high as 20 GPa and improvements including higher elastic modulus and resistance against corrosion. Detailed comparison among samples treated by this process with others treated by conventional method was done using nanoindentation, Auger Electron Spectroscopy (AES) and corrosion resistance testing.