【作者】 田首夫；

【导师】 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 自润滑材料一般由润滑剂和承载相组成，当滑动摩擦时存在润滑剂失效、溅落等问题，在空间环境或高精密仪器仪表环境下适用范围有限，金属材料作为承载体，需要加入大量的固体润滑剂，往往使得力学性能与自润滑性不能同时兼顾，因此设计制备一种既有一定机械强度，又有自润滑性能的材料具有重要的工程意义和材料科学价值。赵敏博士等人发现了TiB₂/Al复合材料具有高强度和自润滑特性，但是对其自润滑机理研究还很不深入。本论文以GCr15轴承钢为对磨件对TiB₂/Al复合材料的自润滑行为及机理进行进一步的的研究。对增强体TiB₂颗粒进行预氧化处理，用压力浸渗法制备TiB₂/Al复合材料，采用扫描电镜（SEM）、透射电镜（TEM）、高分辨透射电镜（HRTEM）对微观组织进行了观察，采用CJS111A型和WTM-2E型销盘式摩擦磨损试验机对材料摩擦学性能进行了测试，并对摩擦学机理进行探讨。摩擦学研究具有系统依赖性和时间依赖性。在系统依赖性方面，TiB₂/Al-GCr15摩擦副的内部因素如复合材料界面结合、增强体体积分数和外部因素如载荷、滑动速度、GCr15的表面粗糙度、真空及氩气气氛试验等诸多条件，并且进行了系统分析和对比研究。在时间依赖性方面，综合各种条件下的磨合曲线，总结并推导出了TiB₂/Al复合材料的自润滑机理。研究发现，TiB₂颗粒预氧化是TiB₂/Al复合材料产生自润滑特性的必要条件。预氧化过后的TiB₂颗粒表面被一层20-30nm厚的由TiO2和B₂O₃组成的混合氧化物包裹。两种氧化物为TiB₂在预热温度下与空气中的O2反应所致。其中反应物B₂O₃及其与空气中的水蒸气反应生成的具有层状结构的固体润滑剂硼酸（H₃BO₃）对摩擦磨损性能有重要影响，这是TiB₂/Al复合材料具有自润滑性的内在因素。增强体体积分数与摩擦学行为研究表明，存在黏着磨损向自润滑状态转变的临界体积分数。体积分数低于24.3%，不具备自润滑性；两者之间为过渡区，自润滑现象的产生受到试验条件的影响；高于31.6%，则具备自润滑性。选取了0.49N、0.98N、1.96N、3.92N载荷研究载荷对材料摩擦磨损性能的影响，结果表明，当载荷≥0.98N时，不具备自润滑特性，载荷为0.49N时，材料在各种速度下出现了自润滑性。可以据此推论：摩擦时在材料表面的润滑膜很薄，承载能力较弱，高载下无法有效的起到降低摩擦的作用。选取0.2、0.5、0.8、1.0、1.5、2.0m/s时的摩擦系数研究了速度对摩擦学行为的影响。结果表明，1)随着速度的升高，摩擦系数从0.5降到0.2。磨损机制也从黏着磨损为主转化成以氧化磨损为主。2)材料自身具备自润滑剂，但是低速下仍然不具备自润滑特性，说明维持自润滑特性仅仅依靠预氧化产生的TiO2和B₂O₃远远不够，需要TiB₂在摩擦热作用下的持续氧化来源源不断的提供自润滑剂。3)自润滑条件下的复合材料磨损表面存在润滑膜，局域分布，且由氧化物混合组成，很薄。本文还研究了GCr15盘的表面粗糙度对摩擦磨损行为的影响。发现存在自润滑现象的最佳表面粗糙度，且该数值与TiB₂颗粒预氧化后氧化物层厚度有紧密联系。设TiB₂的表面氧化物厚度为h，对磨盘的表面粗糙度为Ra。则最佳表面粗糙度的大小与增强体表面预氧化产生的TiO2和B₂O₃层厚度大小相当，在20-30nm数量级，即Ra⁰.02-0.03μm。1)Ra>>h，对应Ra0.606μm和Ra0.372μm。接触时氧化物层无法填满对磨盘微凸体间隙，造成高硬度的对磨盘微凸体对复合材料的磨粒磨损，产生大量犁沟。2)Ra^h，对应Ra0.023μm。接触时氧化物层刚好填满对磨盘微凸体间隙，阻止了对磨盘与基体合金的黏着，减小了摩擦。3)Ra<<h，对应Ra0.005μm。接触时氧化物层能够填满对磨盘微凸体间隙，但是由于表面过于光滑，分子作用占据主导地位，实际接触面积大大增加，黏着作用占据主导地位，摩擦反而升高。摩擦系数曲线的实时变化，是摩擦副体系内各种减小摩擦、增大摩擦的因素互相影响的一种外在表现。对不同载荷、滑动速度、表面粗糙度情况下的摩擦系数曲线进行综合分析，得出预氧化TiB₂颗粒表面氧化物在磨合阶段起作用，平稳阶段主要是摩擦热的积累使得增强体TiB₂急剧氧化，进而提供源源不断的润滑剂，减小了摩擦。TiB₂/Al-GCr15组成的摩擦副体系，产生自润滑现象时，润滑剂产生的来源，一个是预氧化TiB₂引入，一个是摩擦热使增强体TiB₂持续氧化所致。更多还原

【Abstract】 Self-lubricating material is generally used for the solid lubricant as lubricating phase,the metal material as the carrier body, usually a large amount of the solid lubricant is neededto satisfy the lubricating requirment. But the mechanical properties and self-lubrication cannot be satisfied at the same time, therefore one kind of material, which has good mechanicalstrength and self-lubrication is needed.Zhao min has found TiB₂/Al composites can meet the above requirements, but did notanalysis its self-lubricating mechanism in depth. The purpose of this thesis is to investigatethe self-lubricating mechanism of TiB₂/Al composite in detail.The reinforcement TiB₂particles are pre-oxidized, and the pre-oxidation temperature isoptimized, and then TiB₂/Al composites are fabricated by the pressure infiltration method.Microstructure is analyzed by using scanning electron microscopy （SEM）, transmissionelectron microscopy （TEM）, high-resolution transmission electron microscopy （HRTEM）.Tribological properties were tested using CJS111A and WTM-2E type pin-on-disc weartester, and tribological mechanism was discussed.For tribology, there are system dependence and time dependence. The tribologicalsystem is divided into internal and external factors for TiB₂/Al-GCr15system. The internalfactors, including the composite interface and volume fraction; external factors, includingload, sliding speed, surface roughness, vacuum and argon atmosphere. Both factors areinvestigated in detail. Finally, through the study of time-dependence of coefficient offriction, the self-lubricating mechanism of TiB₂/Al composite is deduced..Microstructure observation showed that TiB₂particles after pre-heating were coated byone layer （0.02-0.03μm） of mixed oxide composed of TiO2and B₂O₃. Furthermore, B₂O₃reacted with H2O from the air to generate H₃BO₃, which has good lubrication. This wasthe intrinsic self lubricating factor for TiB₂/Al composites.The investigation of volume fraction showed that there were critical values:non-adhesion wear volume fraction （24.3%） and self lubricating volume fraction （31.6%）.And theoretical calculation showed that the critical volume fraction of non-adhesive wearand self-lubricating,24.3%and31.6%, respectively. Volume fraction of less than24.3%donot have self-lubricating properties; higher than31.6%, self-lubrication is expected;between the two values is the transition zone, self-lubricating phenomenon is affected bythe test conditions.0.49,0.98,1.96,3.92N were selected to investigate the effect of load on tribologicalproperties. Test results show that when load>0.49N, self-lubricating characteristics do notappear, load=0.49N, the material showed self-lubrication. It can be deduced: Duringsliding, the lubricating film of the surface is thin, it can not reduce friction effectively. The microstructure observed after pre-oxidation of the surface oxide layer showed a thickness of20-30μm, which can not withstand a greater load.0.2,0.5,0.8,1.0,1.5,2.0m/s were selected as the experimental conditions toinvestigate the effect of speed on tribological properties. The results show that1) As thespeed increases, the coefficient of friction is from0.5to0.2. Wear mechanism was fromadhesive wear to oxidation wear.2) material has lubricant by itself, introduced bypre-oxidation of reinforcement, but still do not have self-lubricating properties at thelow-speed, which means the maintaining of self-lubricating properties needs a large numberof lubricant, the supply of pre-oxidation of TiB₂oxidized is not enough.3) there wasself-lubricating film in the wear surface, local distributed.Effect of surface roughness of GCr15steel. There was one optimal surface roughnessfor self-lubrication, and the value was related to the thickness of oxide coated TiB₂. SetTiB₂surface oxide thickness as h, surface roughness was Ra. Then, the size of optimalsurface roughness is in the same magnitude of TiO2and B₂O₃layer thickness, equivalent to0.02-0.03μm, i.e. Ra⁰.020-0.030μm.1) Ra>> h, corresponding to Ra0.606μm andRa0.372μm. Oxide layer can not fill the asperity, resulting in a large number of furrows.2)Ra^h, corresponding to Ra0.023μm. The oxide layer just fill asperities on the disc gap, toprevent the adhesion of the disc with the matrix alloy, reducing the friction.3) Ra <<h,corresponding to Ra0.005μm. The oxide layer can fill the disc asperity gap, but the surfaceis too smooth, so that the molecular mechanism is dominant, and the actual contact area isgreatly increased, therefore increased friction.The introduction of pre-oxidation of the oxide layer is embodied in the curve of thecoefficient of friction. Real-time changes in the Coefficient of friction curve, reducingor increasing was an external performance for different factors influencing friction.Coefficient of friction curves in different load, sliding speed, surface roughness wereanalyzed, results show that the pre-oxidation of TiB₂particles influence the coefficientof friction in the initial stage of the friction curve. In a stable stage, the frictional heataccumulation enhanced TiB₂oxidation, providing a steady source of lubricant to reducefriction. For TiB₂/Al-GCr15system, during self-lubricating period, there are twosources of lubricant: pre-oxidation of TiB₂and oxidation of the reinforcement TiB₂during sliding.更多还原