Influence of gas pressure and substrate temperature on PIII nitrocarburizing process of AISI 304 stainless steel

Plasma immersion ion implantation (PIII) has been used to modify the surface properties of 304 austenitic stainless steel (AISI). The influence of working gas pressure, 0.2-1.0 Pa, and substrate temperature, 300-500 degreesC, on the microstructure, treating rate, nitrogen/carbon concentration depth profile, and surface microhardness was investigated. A gas composition of 25% C2H2, 75% N-2, r.f. plasma power input of 350 W, and a negatively biased potential of 30 kV were fixed during the experiment. The experimental results show that the substrate temperature and the diffusion process of nitrogen and carbon depend on the gas pressure inside the plasma chamber. The thickness of the modified layer has been found to be more than 30 mum for samples were treated in the plasma for 60 min. The results show also that the values of diffusion coefficient and surface microhardness of the treated samples are high to be 3.4 x 10(-1) mum(2)/s and 1880 kg/mm(2), respectively. (C) 2004 Elsevier B.V. All rights reserved.