No abstract

Steel surfaces have been coated with Co-based tungsten carbide (WC) in an additive printing process. This process leads to compact and extremely mechanically stable surfaces. We performed tribological measurements using WC counter bodies under dry conditions and severe mechanical load. Low coefficients of friction, even for rough surfaces, were found and the resulting wear rates were extraordinarily small, even when compared to high-quality PVD film with a similar composition. These findings suggest a wide field of application for this novel preparation process for wear-resistive surfaces.

This study considers anisotropic microstructures with typical dimensions of a few 10 µm which have been created on steel surfaces by laser surface texturing (LST). It is shown that the subsequent deposition of thin molybdenum nitride coatings by high-power impulse magnetron sputtering (HiPIMS) leads to surfaces that conserve the surface microstructures and exhibit a remarkably large resistance against mechanical wear. Tribological experiments with steel counter bodies are substantially influenced by the relative orientation of the structures and the wear track. Both friction and wear are shown to be modified by more than 30%, with the main effect being the removal of abrasion particles from the mechanical contact. Experiments with alumina counter bodies that hardly provide wear particles show that the orientation has no effect on the abrasion of the counter body. The novelty of the article lies in the combination of MoN coatings with surface texturing.

Molybdenum nitride layers were deposited onto the substrates of high-speed steel using high-power impulse magnetron sputtering. To control the tribological properties of these wear-resistant surfaces, a sophisticated pretreatment of the substrates was performed. Both the topography and the composition of the surfaces were modified on a length scale of a few micrometers before the deposition of MoN. For that purpose, a microembossing technique was applied that used specifically prepared diamond stamps. Compositional variations are realized by an additional deposition of silver. Modifying the properties of the wear-resistant surface via this substrate engineering method allowed a significant reduction in the coefficient of friction, a change of the dominant wear process and a possible lifetime increase. Changing the surface topography led to a reduction of friction and, therefore, to reduced mechanical work supplied to the surface. Occurring wear was reduced accordingly. The introduction of silver further reduced the mechanical energy that was available for the abrasion process and led to an additional increase in the lifetime of the surface. It was concluded that not only the wear volume, but also the relevant wear mechanisms could be influenced via a substrate modification.

Steel surfaces have been patterned by laser surface texturing (LST) to create anisotropic microstructures with typical dimensions of a few 10 micrometers. The subsequent deposition of thin molybdenum nitride coatings by high power impulse magnetron sputtering (HiPIMS) leads to surfaces that conserve the surface microstructures and exhibit an extraordinarily large resistance against mechanical wear. Tribological experiments with steel counter bodies show a substantial influence of the relative orientation of structures and wear track on friction and wear. It is pointed out that the main effect is the removal of abrasion particles from the mechanical contact. Analogue experiments with alumina counter bodies that hardly provide wear particles show that the orientation effect is absent.