| Owing to the excellent properties of low density,high specific strength,strong heat resistance,etc.,TC4-based self-lubricating composites can be used to make lightweight structural parts in intelligent engineering machinery such as industrial robots and numerical control machines,which are expected to be popularized and applied in smart manufacturing.At present,the structural design and preparation methods are relatively incompolete,resulting in strength defects and unstable lubricating properties of traditional metal-based solid self-lubricating materials.Meanwhile,in the theoretical research,there has been a lack of in-depth research on the influence mechanism of these factors on the lubrication performance,such as the bearing characteristics of soft metal lubricating film,the physical and chemical reactions and self-healing effects that occur on the friction surface and the dynamic evolution and coverage of lubricants on the friction surface.In addition,there are few reports about the research on the detection and evaluation of the wear states of metal-based solid self-lubricating materials.Accordingly,this thesis takes TC4 titanium alloy as the research object,and TC4-based self-lubricating composites with surface microporous channels have been designed and prepared using 3D printing and vacuum pressure infiltration technology.And then through the combination of experimental testing and theoretical analysis,the tribological characteristics,lubrication mechanism and its control elements of TC4-based self-lubricating composites have been systematically studied.Meanwhile,the wear states of TC4-based self-lubricating composites have been evaluated based on Lamb wave characteristic parameter,which has certain reference value and guiding significance for reducing material and energy loss in the friction and wear process,as well as ensuring the safe and reliable operation of mechanical parts.This thesis has achieved the following research results:（1）Based on the characteristics of soft metal solid lubricants,Sn,Ag and Cu are preliminarily determined as the basic components,and a variety of specifications of composite soft metal solid lubricant SnAgCu spherical powders have been designed and prepared.And then the wettability between SnAgCu and TC4 substrate,the residual thermal stress of SnAgCu spreading on the surface of TC4 substrate,and the influence mechanism of hard particles on the bearing characteristics of soft metal lubricanting film have been studied.In addition,the equivalent stresses of TC4 substrate surface with non-holes,straight holes,oblique holes and microporous channels have been analyzed by finite element,and the friction interface structural element model with microporous channels has been established to explore the influence law of structural parameters such as micropore pitch,micropore diameter and the depth of microporous channel on the mechanical properties of TC4-based self-lubricating composites.The studies find that the wettability between composite soft metal solid lubricant 50Sn45Ag5Cu and TC4 substrate is relatively excellent.The equivalent stress of TC4 substrate surface with microporous channels is smaller,and when the vertical depth of microporous channel is 3 mm or 3.5mm,the micropore pitch is greater than 2.5 mm,and the micropore diameter is 0.8 mm or1 mm,TC4-based self-lubricating composites can obtain better mechanical properties.（2）TC4 substrates with different structure parameters of microporous channel have been prepared by selective laser melting technology,and the basic mechanical properties of TC4 samples with the structures of non-holes,straight holes,oblique holes and microporous channels have been compared and analyzed.And then the composite soft metal solid lubricants SnAgCu with different components have been filled into the microporous channels on the surface of TC4 substrate by vacuum pressure infiltration process to prepare multiple groups of TC4-based self-lubricating composites.Moreover,the friction and wear behaviors of TC4-based self-lubricating composites with different lubricant components and structure parameters of microporous channel have been characterized and analyzed using the multifunctional friction testing machine and modern advanced testing technology.The research results show that the mechanical properties of TC4 sample with microporous channel structure is close to the non-holes TC4 sample,and the quality of prepared TC4-based self-lubricating composites is excellent.Meanwhile,when the lubricant composition is 50Sn45Ag5Cu,the vertical depth of microporous channel is 3.5 mm,the micropore pitch is 3 mm,and the micropore diameter is 0.8 mm,TC4-based self-lubricating composites have obtained better tribological performance.（3）The tribological properties of TC4-based self-lubricating composites under different temperatures and loads have been analyzed and compared,and the physical and chemical reactions occurring on the friction surface and the friction reduction and wear resistance mechanism of the lubricating film have been investigated in detail.At the same time,the self-healing effect of the friction surface has been further studied.The research results show that temperature has an important influence on the precipitation and spreading behaviors of SnAgCu,and at 400℃,enough SnAgCu precipitates from the microporous channels to form a relatively complete lubricating film on the friction surface.Therefore,TC4-based self-lubricating composites have obtained the best tribological performance.In addition,adding an appropriate amount of Al2O3nanoparticle to SnAgCu,which can play an excellent synergistic lubrication effect on the friction surface,thus making TC4-based self-lubricating composites still obtain outstanding tribological behavior under heavier loads.The studies also find that during the friction process,SnAgCu and TC4 substrate will undergo different degrees of interfacial reaction,generating some intermetallic compounds Ag3Sn,Cu6Sn5,Cu3Sn,Ti3Sn and oxides CuO,TiO2,etc.,which further improve the self-lubricating properties of the material.Meanwhile,the flow of SnAgCu and Al2O3 nanoparticle on the friction surface and the oxidation behavior of Sn and Cu make the surface of TC4-based self-lubricating composites produce a self-healing effect,thereby greatly improving the tribological and mechanical properties of the material.（4）The coverage of lubricating film on the friction surface of TC4-based self-lubricating composites has been calculated using the image segmentation technology based on FCM algorithm,and a quantitative relation expression between the coverage of lubricating film and the friction coefficient has been established.The results show that the calculated friction coefficients are approximately equal to the experimental friction coefficients,which confirms that the tribological performance of TC4-based self-lubricating composites can be predicted according to the coverage of lubricating film.On this basis,a mathematical model of the relationship between the coverage of lubricating film on the friction surface of TC4-based self-lubricating composites and the structure parameters of microporous channel,the characteristics of the lubricant and the friction test conditions has been further established,and then the influence law of the above factors on the coverage of lubricating film have been explored.The studies find that the structure parameters of microporous channel,lubricant characteristics and friction test conditions have a great influence on the coverage of lubricating film.By reasonably adjusting the above influencing factors,the self-lubricating effect on the friction interface of TC4-based self-lubricating composites can be controlled effectively,thus making the material obtains good tribological properties.（5）A mathematical model that characterizes the relationship between Lamb wave characteristic parameter and the preparation quality and wear state of TC4-based self-lubricating composites has been established,and then TC4-based self-lubricating composites with different preparation qualities and wear stages have been detected and analyzed by the non-linear ultrasonic guided wave detection technology.Subsequently,the preparation quality evaluation criteria and wear state evaluation method for TC4-based self-lubricating composites have been put forward,and furthermore the interaction relationship between the microstructure evolution and Lamb wave characteristic parameter during the wear process of TC4-based self-lubricating composites has been revealed.The studies find that Lamb wave characteristic parameter is proportional to the volume fraction of precipitates from TC4-based self-lubricating composites.Taking Lamb wave characteristic parameter corresponding to the qualified TC4-based self-lubricating composites as the benchmark characteristic parameter,the rapid evaluation of whether the quality of TC4-based self-lubricating composites is qualified or not has been realized.In addition,the research results of the evaluation wear state of TC4-based self-lubricating composites based on Lamb wave characteristic parameter show that the volume of friction surface precipitates and the microcracks formed by the internal stress concentration are the dominant factors that cause Lamb wave characteristic parameter to change. |
