Abstract:
Surface texturing techniques to improve the tribological performance of materials surfaces have been increasingly applied in various engineering fields. However, the exact mechanism of improving the material surface antifriction and wear resistance by surface texturing techniques remains unclear. Therefore, researchers have conducted numerous optimization of geometric parameters and working conditions of surface texture to study the mechanism and application range of surface texturing techniques. Main research findings of surface texture in friction control in recent years are reviewed in this paper. First of all, the friction reduction mechanism and theoretical models under different lubrication conditions are discussed. The state-of-the-art of improving the tribological performance of textured surface in terms of geometric parameters and working conditions is specifically introduced, among them, geometric parameters include surface texturing shape, diameter, depth, area density and arrangement; and working conditions depend on the friction form and operating conditions. The parameters and conditions for improving surface tribological performance are analyzed and summarized based on the vital tribological performance parameters, such as friction coefficient, wear quantity, loading capacity, drag coefficient and lift coefficient. Among geometric features, surface texturing shape, diameter, depth, area density and arrangement are all important parameters that affect tribological properties. When optimizing the surface texturing shape, each one should be optimized individually according to its parameters, and then different shapes obtained by single optimization are compared so as to optimize the texture shape suitable for the working conditions. When the texture diameter and depth are optimized under different working conditions, there is an optimal depth-diameter ratio. When the depth-diameter ratio is too high, the micro-rotating vortex is easy to form in pits, which affects the hydrodynamic lubrication. The area density of the surface texture also has an important impact on the loading capacity and the transformation of the form of lubrication. Under dry friction, boundary lubrication or mixed lubrication, the area density directly affects the surface contact area and the ability to capture worn particles. In a certain range, with the increase of the area density, the friction coefficient decreases gradually, and under fluid lubrication, the area density directly affects the stress distribution of the contact surface. With the increase of area density, the friction coefficient generally decreases rapidly first and then slowly decreases. The effect of texture arrangement on the friction performance is related to the sliding direction. In general, the area density of the surface texture has the greatest impact on the friction properties, followed by the diameter and depth, and finally the arrangement. The friction form has the most significant effect on the friction characteristics. Fluid lubrication has better anti-friction and wear resistance properties than boundary lubrication conditions. The high viscosity lubricating oil has a better hydrodynamic lubrication effect than the low viscosity lubricating oil, and it is easier to change the lubricating state, and the friction reduction effect gets better with the increase of sliding speed and load to a certain extent. At present, the combination of surface texturing with solid lubricant, that is, surface composite treatment technology, can achieve the effect of “1+1>2”. The combination of the solid lubricant coating and liquid lubricant can also play a dual lubrication effect. The operating conditions are also crucial for the effect of surface texturing friction reduction. The operating conditions include relative speed, contact load, lubricating film thickness and relative sliding direction. Under fluid lubrication, with the increase of the sliding speed, the hydrodynamic lubrication effect and loading capacity improve, the optimal depth decreases, the optimal diameter increases, and the optimal area density decreases. In the lower range of load, the friction coefficient can be kept constant at a low value; however, with the increase of load, which will lead to the transition of the friction form to mixed lubrication or boundary lubrication, resulting in more serious wear. The thickness of the lubricating film is also the key factor affecting the anti-friction effect of the surface texture. When the thickness of lubricating film increases within a certain range, the friction coefficient decreases and the loading capacity gradually increases; generally, with the thickness of the lubricating film increases, the optimal depth increases and the optimal diameter decreases. In-depth research on the accurate theoretical model, universal simulation method and development of parameter optimization method to improve tribological performance are the emphases and directions for research in the future. It can provide reference value for the study of shape design, simulation optimization methods, experimental methods and optimization ranges of geometric parameters according to the general rules obtained.