Tribological Behavior of 15^# Aviation Hydraulic Oil

15^# aviation hydraulic oil as a specific type of hydraulic oil has been widely applied in aviation field. In this paper, viscosity-temperature curve of 15^# aviation hydraulic oil was measured utilizing MCR302 rheometer. Investigating the effects of varying operational parameters, a methodical single-factor analysis was conducted. A four-ball tester, equipped with high-grade GCr15 steel balls, provided a rigorous examination of the oil's tribological behavior under different loads, temperatures, and sliding speeds. This analysis was crucial for understanding how each factor independently impacted the friction and wear properties of the hydraulic oil. To elucidate the underlying mechanisms of wear observed under these conditions, a multi-technique approach was adopted for surface analysis. Wear scars were meticulously examined with an optical microscope, which offered a clear initial assessment of the surface topography. For more in-depth analysis, a scanning electron microscope (SEM) provided high-resolution imaging to reveal microstructural details. A white-light interferometer allowed for precise measurements of the wear scar volumes, offering quantitative data on the extent of material removal. Additionally, an X-ray photoelectron spectroscopy (XPS) analysis was employed to identify any chemical alterations on the worn surfaces. The experimental results were revealing. Under increasing load conditions, the 15^# aviation hydraulic oil maintained a relatively consistent friction coefficient. However, the physical dimensions of wear scars—both their radius and depth—intensified, suggesting a higher material removal rate. This phenomenon indicated that while the oil maintains stable friction, its wear protection capabilities were compromised under heavy loading. In experiments with high loads, the dissipated energy required for plastic deformation and the creation of new interfaces within the work of friction increases compared to experiments with low loads. This results in an increasingly higher wear volume growth rate, ultimately exhibiting exponential growth. Temperature fluctuations also played a significant role. While the friction coefficient showed little variation with rising temperatures, a marked decrease in viscosity was noted. This reduction hindered the oil's ability to form protective reaction films on sliding surfaces, leading to more pronounced wear, especially between the critical temperatures of 75~100 ℃, where wear scar diameter saw a substantial increase of approximately 60%. Variations in sliding speed introduced another dimension to the wear behavior. Initially, the friction coefficient showed little change with increasing speed, yet a point was reached where it began to decline. Concurrently, the wear rate showed a decreasing trend, suggesting an improvement in lubricating conditions. Over time, as speed increased, the oil transitioned from a boundary lubrication regime to mixed lubrication, and ultimately to a hydrodynamic state, indicating that the oil film thickness was sufficient to completely separate the sliding surfaces, significantly reducing wear.