Microstructure, Oxidation Resistance and High-Temperature Tribological Properties of CoCrWReAl-xRu-TiC Eutectic Alloys

CoCrWReAl-xRu-TiC eutectic alloys (x = 0, 1, 2.5, and 5 wt.%) were fabricated in a tungsten arc furnace under a protective argon atmosphere using pure metals and amorphous graphite. We examined the phase composition and microstructure of the samples and triboinduced layers using SEM-EDS and XRD. DSC was used to determine their melting temperature. The oxidation resistance tests were performed using a thermogravimetric analyzer under isothermal conditions at 1100 °C for 100 h. Oxidation damage was estimated from weight-gain graphs, oxide layer thickness, the relative area of internally oxidized material, and exterior visual analysis. Wear resistance was tested at 1100 °C under dry ball-on-disc sliding conditions for 2 h against a 10 mm Si3N4 ceramic ball at a normal load of 100 N. Increasing Ru content initially refines the carbide structure and makes their distribution in the cobalt matrix more uniform, increasing alloy hardness and wear resistance. At higher concentrations, carbide morphology changes from fine particulate to coarse split-dendritic, increasing their microhardness and intensifying abrasive wear. The oxidation resistance decreases with increasing Ru weight fraction. The 1 wt.% Ru alloy provided the most favorable balance of melting temperature, oxidation resistance, mechanical, and tribological properties.