Friction and wear behaviour of ion-sulpho-carbonitrided layers on low alloy steels

Abstract

The friction and wear behaviour of the ion-sulpho-carbonitrided layers produced by ion bombardment in the vapour of mixed ammonia-alcohol and carbon disulphide has been studied. The friction and wear tests were carried out under unlubricated, lubricated and under lubricated conditions in the presence of an abrasive. At the same time a comparison of the adhesive wear behaviour of this coating with that of liquid sulpho-carbonitrided, gas tuff-nitrided and high frequency induction hardened coatings was made. The microstructures of the surface and diffusion layer were observed and analysed by optical microscopy, electron microprobe and X-ray diffraction analysis. The hardness-depth gradient of the cross-section of the specimens was measured. The results indicated that the resulting coatings from the ion-sulphocarbonitriding process showed a higher wear rate in the early period under unlubricated conditions, which is considered to be associated with the porosity of the outer part of the compound layer, that is a thick and loose layer containing sulphur. Under lubricated and abrasive-containing lubricated conditions the outer layer is not only able to store oil but also able to hold within itself abrasive particles and therefore showed a lower wear rate even in the early period. Moreover, the next outer part of the compound layer is more compact and firmer and the inner diffusion layer has higher hardness, so that the specimens show a rather lower wear rate in the steady wear period. In the final analysis, the resulting coatings from the ion-sulphocarbonitriding process are very suitable for preventing adhesive wear; in particular their antiseizing behaviour can be improved remarkably.