| The key components of advanced equipment are typical friction pairs,such as bearings,gears and wheel rails,and their tribological performance determines the reliability of the equipment.It is an effective way to extend the service life of friction pairs by using surface texturing to improve the tribological properties of materials,which is one of the hot spots in tribological research.In this paper,laser surface texturing was applied to the surface of 45 steel and titanium alloy,followed by tribological tests under the conditions of starved lubrication and dry friction.The effects of texture parameters on tribological properties were studied as well as the tribological behavior of textured and untextured surfaces during starved lubrication to dry friction.The wear mechanism and the influence of surface texturing were analysed.The main contents and conclusions are as follows.（1）Study on tribological properties of textured 45 steel surfaces under starved lubrication and dry friction.The tribological properties of 45 steel samples with different texture parameters were tested and compared with those of untextured samples under starved lubrication.The results show that texture depth is the main parameter affecting the tribological properties of 45 steel,and the wear rate has a good correlation with the friction coefficient.In the selected texture parameters,the optimal texture parameters is the diameter of 100μm,area density of 10%and depth of 10μm,which has better tribological properties than untextured samples under different loads and sliding speeds.However,the surface texturing has limited effect on improving the tribological properties of 45 steel surface under dry friction.The textured surfaces with a diameter of 100μm,area density of 10%and depth of 15μm have a better tribological properties in comparison.（2）Study on tribological properties of textured titanium alloy surfaces under starved lubrication and dry friction.The tribological tests of titanium alloys with different surface densities were carried out under different loads and speeds in starved lubrication,.The results show that the load has a great influence on the tribological properties of titanium alloy.The average friction coefficient of the samples decreases with the increasing of load,while the sample with a higher surface density has a lower average friction coefficient under the same load.The textured samples with a surface density of 20%can reduce the average friction coefficient of titanium alloy by20%～23%,but the wear rate is higher than the others.The textured surfaces with a surface density of 10%can reduce the average friction coefficient by about 11.4%and the average wear rate by about 49%,which have a good antifriction and wear resistance effect in the load of 12 N and the speed of 4 mm/s.However,the surface texturing has no significant effect on the friction properties of titanium alloy surface under dry friction.In contrast,textured surfaces with a diameter of 100μm,area density of 10%and depth of 10μm have a lower friction coefficient.（3）Study on the tribological behavior of textured 45 steel during the transitional period from starved lubrication to dry friction.The friction tests were carried out under a certain load and speed until the friction coefficient increased sharply.The wear mechanism and the influence of surface texturing were studied by means of scanning electron microscope（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The results show that the friction coefficient of 45 steel surface has obvious stage characteristics during the transition period from starved lubrication to dry friction.It can be divided into stable state,variation state and dry friction.The existence of surface textures can effectively prolong the stable state and reduce the friction and wear in the variation state.A layer of friction film（Fe2O3）is formed in the process of friction,which can protect the steel surface and reduce the direct contact of metals.A fresh metal surface is exposed when the friction film is ploughed by the steel ball,and then the fresh metal is oxidized to form a new friction film.The dynamic process of friction film formation can be maintained for a long time due to the secondary lubrication and wear debris collection of surface textures,resulting to an outstanding triboligical properties of the surfaces.（4）Study on the tribological behavior of textured titanium alloys during the transitional period from starved lubrication to dry friction.The effects of single treatment and processing sequence of duplex treatment,as well as the surface density on the tribological properties of titanium alloy were studied.Friction vibration and heat monitoring are introduced as auxiliary criteria for the transition of starved lubrication to dry friction,thus allowing the online monitoring of friction state during the operation of friction pairs.The morphology and element distribution of worn surfaces were investigated by micro analysis technologies in different stages of the friction and wear process,and the mechanism of improving the tribological properties of titanium alloys by TO-LST treatment was discussed.The results show that the LST treatment has limited effect on the tribological properties of the original surface.Zr Ti O4 oxide layer can be formed on the surface of titanium alloy substrate through thermal oxidation,which significantly improves the surface characteristics of titanium alloy.The surface textures can prolong the low friction state by reserving oil and trapping wear debris,thus reducing the friction coefficient and wear rate,which is conducive to reducing the wear of the oxide layer.The existence of the oxide layer,in turn,can contribute to the effective lubrication of the surface.Therefore,TO-layer and LST can further improve the tribological properties during the transitional period from oil starvation to dry friction.The processing sequence of the two treatments has little effect on the tribological properties.The samples with texture surface density of 10%（TO-10%LST and 10%LST-TO）have excellent tribological properties during the friction process regardless of the processing sequence.In summary,this paper reveals the variation characteristics of the tribological properties during the transition period from starved lubrication to dry friction,and clarifies the mechanism of surface texture to improve the tribological properties during the transition period.The research results are expected to enrich the tribilogical theory of starved lubrication and dry friction,and also provide data and theoretical support for tribological properties improvement and the engineering application of laser surface texture. |
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