Research on Surface Micro-Texture Lubrication and Drag Reduction of Cr₁₂MoV Mold Steel

Surface micro-texture demonstrates outstanding performance in lubrication and drag reduction, and is extensively utilized in areas such as mechanical seal, cylinder liner-piston ring, bearing lubrication, tool drag reduction and others. With the continuous enhancement of the power level of aerospace electromechanical servomechanism and the increasingly severe service environment, the friction performance between the slide valve pairs, which is the key components of the servo valve where motion contact occurs is gaining growing significance. The sliding interface of the slide valve pairs of the servo valve has emerged as the primary factor influencing the precise random movement of the servo valve in accordance with the system command signal. There exists sliding friction between the valve core and the valve sleeve, featuring a small contact area, a short reciprocating distance and a high friction frequency. Hence, the influence of friction and wear is more substantial, which will not only lower the transmission efficiency, but also impact the reliability and service life of the mechanism. Cr₁₂MoV mold steel is one of the essential materials of the slide valve pairs within the aerospace electromechanical servomechanism. To diminish the frictional resistance of the relative contact surface, enhance the transmission efficiency and reliability of the mechanism, hydrodynamic simulation on the micro-textures of square, circle, rhombus and regular hexagonal shapes was conducted by employing ANSYS Fluent software under various micro-texture spacings, depths and different minimum oil film thicknesses with the aim of analyzing the influence of different micro-textures on the lubrication performance of friction pairs. Moreover, the surface micro-textures of Cr₁₂MoV mold steel were fabricated by femtosecond laser. Coupled with the friction and wear test, further research was carried out on the optimal micro-texture morphology of the texture treatment. The results demonstrated that the rhombus micro-texture could more effectively induce and enhance the irregular movement of fluids, such as vortices and augment the influence of the inertia effect. The rapid alteration of the local velocity of the fluid was prone to cause the reduction of local pressure to form bubbles, which providing advantageous conditions for the emergence of the cavitation effect. Under the test temperature of 40 ℃, the relative speed between the friction pair surfaces exerted a significant influence on the tribological lubrication properties of Cr₁₂MoV mold steel, while the load, the micro-texture morphology and the micro-texture spacing had less influence. Compared with the surface without micro-texture, the resistance reduction rate of the optimal rhombus micro-texture parameter was 37.74%. Additionally, through SEM and confocal 3D wear topography, it was discovered that the surface micro-texture was beneficial for the formation of the lubricating oil film between the friction pairs of Cr₁₂MoV mold steel, reducing the risk of direct contact between the friction pairs and enhancing the wear resistance.