Study On Surface Texture And Solid-liquid Lubrication Materials For Improving Tribological Properties Of Titanium Alloys

Titanium?Ti?alloys are widely employed in many fields such as aerospace and medical science owing to their high strength,high temperature resistance and excellent corrosion resistance.However,the high plasticity,low hardness,low wear resistance and sensitivity to fretting wear limit their usages in some harsh conditions.Surface texture technology and favorable lubricant have good effect on promoting the friction and wear properties of friction pairs.In order to improve the tribological characteristics of titanium alloys,the study on surface texture and solid-liquid lubrication materials is carried out in this work.Firstly,texture structures with varying dimple diameters and densities are produced on titanium alloy surface by laser processing technique,and the influence of laser marking parameters on texture morphology and depth is discussed.The process parameters are optimized according to the characterization results of textured surface,and then optimal marking parameters are obtained.Secondly,the friction and wear behaviors of the resulting titanium alloy with different texture structures are evaluated by linear reciprocating friction mode.The results show that the textured titanium alloy surfaces with morphology of 200?m dimple diameter and 8.7%dimple density exhibit the best anti-wear and friction-reducing ability among all modified samples,which is mainly due to the accumulation of debris in the dimples and thus reducing wear caused by third-body.ANSYS Workbench is used for finite element simulation of rubbing process on textured surface.The results reveal that large texture density leads to excessive local contact stress on the interface and wear aggravation.The simulation results are in good agreement with the experimental results.Furthermore,the tribological properties of typical texture forms under 10W40 and PFPE lubrication are discussed.The results show that the textured titanium alloy surfaces with morphology of 200?m dimple diameter and 19.6%dimple density have best friction-reducing ability under 10W40 lubrication,and the effect of friction reduction on texture surface is more obvious when the friction speed is higher,which is due to that higher friction speed is more conducive to enhance the micro-fluid hydrodynamic bearing effect of texture surface.Under PFPE lubrication,the textured surfaces with morphology of 200?m dimple diameter and8.7%dimple density display best friction-reducing ability,which can be interpreted as follows.During the rubbing process,the surface texture can improve the lubrication state,and on the other hand the increase of contact stress leads to more formation of metal fluoride FeF₂ on the friction surface.The FeF₂ can be used as solid lubricant which is benefit for friction reduction and wear resistance.Finally,the 1H,1H-perfluorooctylamine?FOA?is covalently grafted onto the GO surfaces and then the product is reduced for synthesizing a modified graphene nanomaterial of FOA-rGO,and the tribological performances of GO,rGO and FOA-rGO dispersed in PFPE respectively for lubricating titanium alloys are discussed.The results show that FOA-rGO nanosheets disperse uniformly in PFPE oil without any obvious deposites and aggregates compared to GO and rGO.The friction coefficient is reduced by 52.7%and the wear rate is reduced by almost 5 orders of magnitude,when compared to the pure PFPE.The excellent lubricating ability of FOA-rGO is closely related to its excellent dispersibility in PFPE that favors the formation of a thin,durable,and stable boundary tribofilm between the contact surfaces.The homogeneous tribofilm together with the PFPE oil can form a stable solid-liquid lubrication film in the contact area and hence prevent the friction pairs from directly contacting during rubbing process.Further,lubrication characteristics of FOA-rGO/PFPE on different texture surfaces are evaluated,and the results reveal that the synergistic lubrication effect between PFPE oil containing modified graphene additives and surface texture is poor,which is due to that it is difficult for graphene to form a stable and uniform friction film on textured surface.