Sliding wear resistance of the Cobalt-Based Coatings, ULTIMETTM and STELLITETM 6 with ruthenium additions

Abstract

Two different cobalt-based bulk alloys, ULTIMETTM and STELLITETM 6B, their high velocity oxygen fuel (HVOF) spayed coatings with minor additions of ruthenium and mild steel substrate were subjected to ball-on-disc sliding wear tests at 5 N and 10 N and hardness tests at 3 kg. These materials were targeted as replacements or protective coatings on mild steel for better wear resistance. Their microstructures comprised γ-austenite and Cr3C2 phases, and coefficients of friction fluctuated slightly. The coatings had good wear resistance (0.2 ± 0.0x10-5–5.6 ± 0.2x10-5 mm3·N−1·m−1) and higher hardnesses (386 ± 21–547 ± 39 HV3) than the alloys (304 ± 22–368 ± 13 HV3) and mild steel (180 ± 14 HV3). After wear, bulk and coated samples exhibited tearing, slip bands, grooves and debris. The best alloy was STELLITETM 6 coating with 0.6 wt% Ru addition which had low wear rates both at 5 N (0.2 ± 0.0x10-5 mm3·N−1·m−1) and 10 N loading (0.5 ± 0.0x10-5 mm3·N−1·m−1), and was the hardest (547 ± 39 HV3).