Investigation of HVOF-sprayed (Ti,Mo)(C,N)-Ni hardmetal coatings for static friction applications

Hardmetal coatings produced by high velocity oxy-fuel (HVOF) spraying are intensively studied for sliding wear protection, where commonly a low kinetic coefficient of friction is required. However, these coatings have also a high potential to serve as a coating solution for components requiring a high static coefficient of friction. As part of a systematic study, in this work the static coefficient of friction of as-sprayed (Ti,Mo)(C,N)-Ni hardmetal coatings in torsion experiments with different contact pressures was studied and is reported in detail. The coatings were sprayed from an experimental feedstock powder with a liquid-fuelled HVOF gun. Geometric parameters, as the number of islands, the mean surface of the islands and the volume of the material for a specific evaluation height c of the friction surface have been investigated together with its form and orientation. The slipping curves have been determined and static coefficients of friction µ0.1 up to 0.66 and µmax up to 0.80 were measured. The results show a decreasing standard deviation with increasing nominal contact pressure. After the slipping experiments, both the coating surfaces and the metallographically prepared cross sections have been studied in detail. It has been found that material from the counterparts has been transferred to the coating surfaces.