Tribological behavior of 3J1 paired G95Cr18 under 15# aviation hydraulic oil lubrication

The aviation industry is increasingly demanding higher speeds, loads, and temperatures, necessitating the urgent development of a new friction and wear system. This article examines the tribological behavior of Ni36CrTiAl (3J1) and G95Cr18 in 15# aviation hydraulic oil. We selected a pair and employed a UMT5 multifunctional friction and wear tester for the study. Our results indicated that as speed increased, the system’s friction coefficient initially rises, then falls, before rising again. Concurrently, the wear scar diameter steadily increased. As the speed increased, the friction coefficient of the system increased from 0.103 (10 mm/s) to 0.122 (30 mm/s), then decreased to 0.095 (75 mm/s), and finally increased to 0.101 (100 mm/s). When 3J1 and G95Cr18 were lubricated with 15# aviation hydraulic oil, the friction coefficient was at its minimum of only 0.095 when the rotational speed was at 75mm/s. This indicated that the lubrication conditions for this system were optimal under these circumstances. A long-wear experiment was conducted for 30 minutes under conditions of 5N, 75mm/s, and room temperature, followed by testing the friction coefficient of the system at different speeds. The results revealed that as the speed increases, the system enters a state of mixed lubrication. Observations from the microscope showed that as the speed increased, the carbon film gradually wears away and a new friction reaction film gradually forms at a rate faster than its consumption. Therefore, the friction coefficient was at its lowest at this point, but the wear scar enlarged. Calculations from 3D-light topography interferometer data showed that the wear rate was at its lowest at 75mm/s, being only 4.1×10-7 mm3/(N·m). As the speed changed, the primary wear mechanisms were abrasive wear and adhesive wear. The system exhibited the same trend with increased load as it does with increased speed. As the load increased, the friction coefficient of the system increased from 0.092 (1 N) to 0.133 (3 N), then decreased to 0.095 (5 N), and finally increased to 0.102 (10 N). Additionally, a long-wear experiment was conducted for 30 minutes under conditions of 5N, 75mm/s, and room temperature, followed by testing the friction coefficient of the system at different loads. The results showed that as the load increased, the system remained in a state of mixed lubrication. As the load increased, the wear rate gradually decreased. When the load is 10N, the wear rate was at its lowest, being only 9.8×10⁻⁸ mm³/(N·m). As the load changed, the primary wear mechanisms remained abrasive wear and adhesive wear. We also investigated the impact of temperature on the system’s friction performance. The friction coefficient showed a trend of first decreasing, then increasing, and then decreasing with the increase of temperature. As the temperature increased, the friction coefficient of the system increased from 0.095 (room temperature) to 0.131 (95 ℃) and finally decreased to 0.107 (155 ℃). This was due to the formation of carbides in the contact area, which significantly reduced the friction coefficient and fluctuates greatly. The friction coefficient showed a trend of first decreasing, then increasing and then decreasing again as the temperature increased. Notably, when the temperature rises to 155℃, 15# aviation hydraulic oil carbonized, and the generated carbon benefited friction wear. However, the consumption of carbon intensifies the friction in the wear area, therefore the friction coefficient began to rise again. When the temperature was at 75℃, the wear rate was at its lowest, being only 4.3×10⁻⁸ mm³/(N·m), which was 13.9% of the wear rate at 35℃. As the temperature changed, the primary wear mechanisms were abrasive wear and adhesive wear, and as the temperature rose, the characteristics of adhesive wear became more apparent. Optimal friction performance was achieved when the speed was 75 mm/s, the load was 5N, and the temperature was at room level. Further exploration of the friction mechanism via X-ray photoelectron spectroscopy (XPS) revealed the formation of a reactive oxide film in the friction area. This was key to achieving high-performance friction and wear. Our study provided theoretical guidance from a tribological perspective for material research in the next generation of aviation.