Low- and high-energy plasma immersion ion implantation for modification of material surfaces

Low- and high-energy plasma immersion ion implantation (PIII) of nitrogen has been performed on austenitic stainless steel and high-carbon low-alloy steel to modify their surface properties. In the case of austenitic stainless steel, an expanded austenite layer with surface microhardness of 650 HV was formed with a thickness of 7–8 μm for an elevated treatment temperature of 400 °C, irrespective of the treatment energy. X-Ray photoelectron spectroscopy (XPS) investigations revealed that, at high energy, nitrogen is in a bound state and chromium nitride is formed in the subsurface region, followed by expanded austenite. In the case of high-carbon low alloy steel, the diffusion coefficient of nitrogen obtained by PIII is higher than that obtained by glow-discharge plasma nitriding. The results indicate that if implantation is followed by diffusion, low-energy PIII gives similar or better results than high-energy PIII as far as the treated layer thickness, phase formation and microhardness are considered. Low-energy PIII has a lower hardware cost and reduced sheath dimensions, and thus uniformity in surface modification is achieved.