Tribological investigation of surface structures processed by high-feed milling on HVOF sprayed WC-12Co coatings

Abstract

Since properties of high-velocity oxy-fuel (HVOF) sprayed WC-12Co coatings are limited due to the inherent restrictions of the material, new approaches that involve tailored surfaces and designing friction properties of functional materials have attracted enormous interest. Within this scope, two different deterministic patterns are machined on as-sprayed and polished WC-12Co coatings by means of a high-feed milling (HFM) process, whereby different process parameters with respect to the feed per tooth as well as the lead angle are taken into account. The produced high-feed milled surfaces are investigated with respect to the resulting topography and tribological properties under dry sliding conditions.The tribological examination of the high-feed milled surfaces reveals a decreased coefficient of friction (COF) compared to the polished WC-12Co coating sliding against a 100Cr6 counter-body. The lower friction is attributed to the reduction of the contact area as well as the capability of the cavities to store the transferred material resulting from wear debris. With respect to the different surface patterns, higher values for the kurtosis Sku lead to a reduction of friction. In contrast to the results presented for 100Cr6, the WC-12Co surfaces sliding against Al2O3 counter-bodies exhibit an almost constant COF for all surfaces. Although the reduced contact area leads to increased tribological stresses, the processed surfaces show a high resistance to sliding wear. Finally, it is clarified that time- and cost-consuming mechanical surface treatments such as polishing or grinding prior to a subsequent HFM process do not have to be applied. Therefore, HFM enables a new manufacturing route to structure WC-12Co coatings as well as to modify the tribological properties.