INFLUENCE OF THE INTRINSIC COATING PROPERTIES ON THE CONTACT MECHANICAL STRENGTH OF PERFECTLY ADHERING CARBON-DOPED AISI 310 PVD FILMS

Conventional single pass and unidirectional multipass scratch testing has been used to study the contact mechanical strength of reactive magnetron sputtered AISI 310 SS deposited on construction steel and high speed steel substrates (AISI 4137 and M2). The coatings, doped with different amounts of carbon for microstructure modifications, are shown to be perfectly adhered to their substrates. At the high contact pressures used in scratch testing surface damage is, above all, ductile plastic deformation related to a system scratch hardness essentially controlled by the substrate. Surface cracking, especially brittle and tensile, through thickness cracks is detrimental with respect to wear behaviour. Owing to transfer layer build-up, cemented carbide indenters which allow more realistic adhesive friction enhance surface crack formation. Multipass scratch testing under constant low and medium loads in conjunction with damage volume assessment using three dimensional profilometry yields detailed information on the surface damage mechanisms under contact mechanically more realistic conditions. This leads to considerably better prediction of system strength with respect to wear. For the high friction, cemented carbide indenter system strength optimization has been obtained for a 2 wt.% carbon-doped mixed (microcrystalline and amorphous) coating corresponding to a mechanical compromise between high composite hardness and toughness.