Study of corrosion resistance and surface properties of carbon steel aftera duplex plasma treatment

The aim of this work was the improvement of the corrosion resistance, of th e hardness and of the tribological properties of a commercial steel by a co ld plasma treatment consisting of a nitriding treatment (N-2/H-2 useful 25% N-2/75% H-2) followed by carbon treatment (CH4/H-2 useful 5% CH4, 95% H-2) in an inductively coupled plasma reactor with a radiofrequency generator ( 40 MHz). This type of treatment was called duplex treatment. Optical emissi on spectroscopy (OES) was used to characterize both N-2/H-2 and CH4/H-2 dis charges. The modifications of the corrosion resistance characteristics of t he steel due to the treatment were investigated by electrochemical tests. S urface analytical techniques (dynamic secondary ion mass spectroscopy, X-ra y photoelectron spectroscopy, atomic force microscopy and scanning electron ic microscopy) were also used to study the modifications of the surface com position and of the superficial layer. It was shown that a nitriding treatm ent improves the hardness and also the corrosion resistance, yet to a lesse r extent than the duplex treatment. A protection rate (7) as high as 99.6%, relatively to the non-treated sample, together with an increase of the har dness from HV1g = 280 to HV1g = 950 for the duplex steel were obtained. The morphological and chemical analysis showed the formation of a uniform stru cture on the surface with an enrichment in carbon and nitrogen, and the pre sence of oxygen. (C) 2001 Elsevier Science B.V. All rights reserved.