Tribological behaviour of atmospheric plasma and high velocity oxy-fuel sprayed WC-Cr3C2-Ni coatings at elevated temperatures

Abstract The thermally-sprayed coatings extensively used in high temperatures application such as aerospace, power generation equipment, hot section components in gas and steam turbines. Most of the thermally sprayed WC based coatings lost the functional ability after 500 °C. Consequently, the work focuses on the development of WC based coatings which could sustain with excellent functional ability even above 500 °C. The unidirectional dry sliding wear of WC-Cr3C2-Ni coatings deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) techniques have been relatively investigated up to 800 °C using ball-on-disc high-temperature tribometer (ASTM G99). The scanning electron microscopy (SEM), energy dispersive X-ray analyser (EDX) and Raman spectroscopy analysed the worn-out surface morphology, oxide content and phase transition. The detailed wear mechanisms at 300 °C, 500 °C and 700 °C were studied. Interestingly, the specific wear rates of both the coatings were declined after 500 °C. The study of the relationship between wear and tribo-oxidation process suggested that HVOF coatings inhibit the wear above 500 °C, due to development of tribo-film and well retained WC phase on the surface even at high temperature. The lubricous oxides WO3, NiWO4 and CrWO4, attributed to form a tribo-oxide film which resulted into superior wear resistance up to 800 °C. Nevertheless, specific wear rates for both coatings are in a mild regime which recommended that WC-Cr3C2-Ni coatings could be more durable up to 800 °C in the oxygen-enriched environments.