Dual-Film Synergistic Lubrication Mechanism of Sulfurized Oleic Acid Butyl Ester/Modified Castor Oil System in Machining GH4169 Nickel- Based Superalloy

GH4169 nickel-based superalloy is widely used in aerospace critical components manufacturing due to its excellent high-temperature strength, oxidation resistance, and corrosion resistance. However, its machining process often results in issues such as high cutting forces, severe tool wear, and poor surface quality. To address these challenges, a novel green dual-functional cutting fluid system was designed and formulated in this study. The system uses ethoxylated modified castor oil (E-S545) as the base oil and incorporates sulfurized oleic acid butyl ester (SOE) as an ash-free extreme-pressure additive, thereby constructing a composite lubrication system with synergistic physical adsorption and tribochemical reaction mechanisms.High-temperature tribological tests (100–500°C, 100–200 N) and actual turning experiments on GH4169 were conducted to systematically evaluate the friction-reducing, anti-wear, and thermal stability performance of the SOE/E-S545 system. The results showed that the formulated cutting fluid exhibited a remarkably low steady-state friction coefficient of 0.009 at 100°C and 100 N, due to the rapid formation of a dense and stable adsorption film. Even under extreme conditions of 500°C and 200 N, the friction coefficient remained as low as 0.324, demonstrating excellent high-temperature lubrication stability.Cutting experiments further verified that this system significantly reduced cutting forces (up to a 25% reduction) and slowed down the tool wear rate. The tool wear width gradually increased from 237 µm at 10 minutes to 350 µm at 50 minutes, with a uniform and stable wear morphology. SEM, EDS, and XPS analysis revealed that E-S545 formed a uniform physical adsorption layer on the metal surface, while SOE generated FeS and FeSO₄ tribochemical films under high temperature and high pressure. The two layers intertwined to form a continuous and dense "dual-film lubrication" structure, effectively suppressing oxidative wear and metal adhesion.The SOE/E-S545 system achieved excellent friction reduction and anti-wear performance under high-temperature and high-load conditions through a "physical adsorption + chemical reaction" dual lubrication mechanism. This system avoids the environmental hazards associated with traditional chlorine-containing extreme-pressure additives and provides a theoretical basis and formulation design idea for the green machining of nickel-based superalloys.