Analysis of the Lubricating Properties of the Internal Structure Asymmetric Microtexture on the Material Surface
Microtexture has been proven to have an important role in wear reduction and lubrication of material surfaces,but the internal structure of a symmetric microtexture is more homogeneous in terms of friction direction and lubrication mode.Therefore,studying the symmetry of the internal structure of a microtexture is vital.This study investigated the effect of the internal-structure asymmetric microtexture on the process lubrication characteristics and incentive mechanism to improve the material surface friction properties.Two lubrication states,the internal-structure symmetric and asymmetric groove microtextures,were simulated using the fluid-solid coupling method.By simulating the forward and reverse friction behavior of the symmetric microtexture and two internal-structure asymmetric microtextures,we determined the microtexture parameters and friction direction when the internal-structure asymmetric microtexture reached the optimal lubrication state and analyzed the effect of the symmetry of the internal structure of the microtexture on the cavitation and inertia effects by studying the pressure distribution,flow rate,and flow traces of the lubricant in the microtexture unit.The internal structure of the asymmetric microtexture was prepared via a tilting process using a femtosecond laser,and frictional wear experiments were conducted using an MPT-20 wear tester.The results showed that the internal-structured asymmetric microtexture exhibited better lubricity and friction performance under the conditions of lubricant inertia effect and cavitation effect,and the internal-structure asymmetric microtexture had better performance in forward friction lubrication.Comparing the pressure distribution graphs,flow velocity graphs,and flow traces of the asymmetric microtextures of the two internal structures,we observed that the lubricity of the microtexture grooves was superior when the grooves had right angles,both for forward and reverse friction;the best internal-structure asymmetric microtexture had an oil-film bearing capacity of 146 227 Pa and the fastest flow rate of 6.695 m/s.The inclined machining process was beneficial for improving the microhardness and wear resistance of the material surface.The average microhardness of the machined surface was 1 766.70 HV,which was approximately 11.9％higher.Additionally,a significant reduction in the wear rate with multilevel bonded wear on the unprocessed surfaces was observed,whereas the laser-processed surfaces had a smaller wear area and less bonded wear,and the degree of surface strengthening increased with increasing inclination.The wear rate of the asymmetric surface microtexture of the optimal internal structure was 10.08× 10-3 mm3/(N·m)and the friction factor was 0.0932,which was a reduction of the friction factor of approximately 13.1％.The results proved that the symmetrical characteristics of the internal structure of the microtexture directly affect the flow velocity and the state of the flow traces of the lubricant,which consequently affects the bearing capacity of the oil film.The greater the flow velocity,the more intense the cavitation effect,and the more complex the flow traces,the more concentrated the vortex center,and the stronger the inertia effect.The friction factor of the surface with an internal-structure asymmetric microtexture was smaller than that of the surface with a symmetric microtexture,and the friction factor of the right-angle microtexture was the smallest.The processing of an internally structured asymmetric microtexture can increase surface hardness,and a laser-induced periodic nanostructure(LIPSS)facilitates a reduction in the friction factor.The experimental results matched the simulation results,laying the foundation for the application of internal-structure asymmetric microtextures in the manufacturing industry and enriching the types of material surface microtextures.
万方数据
维普
