Influence of oxidation on the dry sliding properties of HVOF-sprayed hardmetal coatings

In order to investigate the influence of the oxide scales on their tribological behavior the tribological properties of a variety of preoxidized hardmetal coatings (WC-CoCr, WC- (W,Cr)2C-Ni, Cr3C2-NiCr, (Ti,Mo) (C,N)-Ni, (Ti,Mo) (C,N)-Co) against sintered alumina were studied in an unlubricated dry sliding wear test. Tests were performed at room temperature, 600 deg C and 800 deg C with sliding speeds in the range 0.1-3 m/s with a wear distance of 5000 m and a normal force of 10 N. For comparison, preoxidized electrolytic hard chromium and APS-sprayed (atmospheric plasma spraying) Mo-NiCrBSi coatings were studied in the same conditions as well as APS-sprayed Cr2O3 coatings. The results of preoxidized coatings in this work are compared with those of non-oxidized coatings in previous experimental series. Preoxidation of hardmetal coatings did not lead to an improvement of the sliding wear resistance.