Utilisation of PVD Hard Coating after Electron Beam Surface Treatment for Cast Iron

摘要

Wear protection plays an important role for highly loaded components. Therefore, PVD hard coatings with very high hardness have become well established in industrial applications for steel components in the automotive industry. As an alternative to steels, efforts are currently being focused on cast irons for components because of their reduced requirements for superior properties in machining, their lower weight, and lower costs. However, due to the insufficient load-bearing support of this soft base material and/or of their individual micro-structural constituents (graphite), the use of hard coatings on cast irons for wear protection has remained limited. The present contribution deals with the possibilities with respect to using electron beam (EB) solid phase treatment (hardening) and liquid phase surface treatments with Ni-based additives (alloying) and without additives (remelting), to improve the conditions for deposition and the load-bearing support of the thin PVD hard coatings. Apart from the hardness of the EB-treated layer, the toughness of the specific microstructural constituents influences the properties of the composite layer substantially. Comparative studies of different single treatments and duplex treatments (EB treated and, subsequently, PVD hard-coated) were carried out by means of unlubricated pin-on-disc wear tests and potentiodynamic corrosion measurements in a 5% NaCl Solution. The investigations proved that it is possible to use PVD hard coatings (with all their outstanding properties) for cast iron components by utilising duplex surface treatment technologies.