METALLIC INTERLAYERS BETWEEN STEEL AND DIAMOND-LIKE CARBON

Many processes for the deposition of diamond-like carbon (DLC) are carried out just above room temperature. The low process temperature makes it simple to coat a wide variety of materials but can lead to serious adhesion problems between the coating and the substrate. In this work DLC coatings on steel for tribological applications were developed. DLC was deposited on stainless steel (DIN 1.4305) by pulsed laser ablation of graphite. Generally the adhesion of DLC on steel was very poor. By applying different metallic interface layers (e.g. Cr, Mo, Si, Cu), the adhesion has been improved considerably. The microstructure of the interfaces has been studied by cross-sectional transmission electron microscopy, including high resolution imaging and electron diffraction, but no evidence for a crystalline reaction zone was observed. The adhesion of the coating has been tested by ultrasonic cavitation and the scratch test. A rank order of intermediate layer metal combinations was established. Generally the combination of Cu and a metal belonging to one of the IVb, Vb or VIb groups of elements was observed to give good adhesion. Cu/Cr appeared to give the best adhesion.