To meet the urgent demand for long service life and high reliability surface coatings for critical components in strategic fields such as aerospace and automotive energy, it is essential to overcome the limitations of conventional coatings in simultaneously achieving friction reduction and wear resistance. In this study, (TiNbCrMoV)C high-entropy carbide ceramic coatings were prepared on GH4169 substrates by ion source-assisted direct current magnetron sputtering based on a multi-principal-element synergistic strengthening and toughening design concept. The effects of CH4 flow rate on the microstructure, mechanical properties, residual stress, and tribological behavior of the coatings were systematically investigated. The results showed that at low CH4 flow rates of 0 and 5 cm3/min, the coatings were mainly composed of a BCC metallic solid solution and exhibited a typical columnar grain structure. Under these conditions, the coatings showed relatively low density and hardness due to insufficient carbon participation, but good adhesion strength was maintained owing to the dominance of metallic bonding and favorable interfacial compatibility with the substrate. As the CH4 flow rate increased, carbon incorporation was significantly enhanced, which promoted the formation of metal-carbon (Me-C) bonds and effectively suppressed grain growth. Consequently, the coating structure gradually evolved from columnar grains to nanocrystalline or amorphous states, accompanied by a marked increase in coating density. When the CH4 flow rate reached 10 and 12 cm3/min, the coatings exhibited a fully amorphous structure and achieved the maximum hardness of 979HV. At the same time, the residual stress remained at a moderate compressive level of approximately -0.8 GPa, and good adhesion strength was preserved, indicating an optimized balance between mechanical performance and stress state. With a further increase in CH4 flow rate to 15 and 20 cm3/min, the coating structure transformed into an FCC phase, accompanied by the precipitation of an amorphous carbon (a-C) phase. Excessive carbon incorporation led to a significant increase in surface roughness and residual compressive stress, while the hardness decreased sharply. At 20 cm3/min, the surface roughness, residual stress, and hardness reached 35.8 nm, -2.21 GPa, and 651HV, respectively, reflecting a deterioration in load-bearing capacity. Tribological tests indicated that the friction coefficient decreased monotonically with increasing CH4 flow rate due to the lubricating effect of the a-C phase. In contrast, the wear rate first decreased and then increased. At a CH4 flow rate of 15 cm3/min, the coating exhibited optimal tribological performance, with a friction coefficient of 0.54 and a minimum wear rate of 8.57×10-7 mm3/(N·m). Under this condition, a stable third-body layer was formed during sliding, consisting of a carbide load-bearing framework synergistically combined with multi-metal oxides and a-C lubricating phases, which enabled the cooperative optimization of high load-bearing capacity and low shear strength. However, when the CH4 flow rate increased to 20 cm3/min, excessive a-C precipitation further reduced the friction coefficient but degraded hardness and surface quality, resulting in a sharp increase in wear rate to 8.56×10-6 mm3/(N·m), which was one order of magnitude higher than that at 15 cm3/min. In summary, rational regulation of CH4 flow rate plays a critical role in tailoring the microstructure, mechanical properties, stress state, and tribological performance of (TiNbCrMoV)C high-entropy carbide ceramic coatings. Optimized carbon incorporation effectively enhances coating density and mechanical strength, improves stress conditions, and promotes favorable lubrication and wear resistance, thereby achieving the synergistic optimization of coating structure and tribological performance.
Key words
high-entropy carbide ceramic coating /
direct current magnetron sputtering (DCMS) /
CH4 flow rate /
microstructure /
mechanical properties /
friction and wear
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Funding
National Natural Science Foundation of China (51401182); Guangdong S&T Program (2025B0101030001); Guangdong Basic and Applied Basic Research Foundation (2024A1515010753); Program of Open Project of the State Key Laboratory of New Brazing Materials and Technology (SKLABFMT-2023-09)
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