铜基自润滑复合材料的制备及摩擦磨损性能研究

【作者】 张伟；

【导师】 肖金坤； 施国春；

【作者基本信息】 扬州大学 ， 机械工程（专业学位）， 2019， 硕士

【摘要】 铜基自润滑复合材料兼具金属基体良好的力学性能和物理化学性能,以及固体润滑剂优良的摩擦学特性,适合在化学、电气、高低温、重载、高真空、强辐射等一些不宜采用油润滑的特殊工况下工作。揭示铜基自润滑复合材料摩擦磨损机理,发展摩擦表面关键特征的定量表征新方法,建立相关模型,是金属基自润滑复合材料的设计和应用领域急需解决的关键问题。本文通过粉末冶金热压法制备铜-二硫化钼和铜-二硫化钨自润滑复合材料,主要研究以上两种材料的组织结构演变和摩擦磨损行为,建立并验证了金属基自润滑复合材料摩擦模型。具体内容如下:(1)研究MoS2含量对Cu-MoS2复合材料摩擦磨损性能的影响发现,在MoS2添加含量低于20 vol%时,MoS2对降低铜基复合材料的摩擦系数非常有效。然而,在复合材料中进一步添加MoS2,几乎不能降低摩擦系数,这与磨损表面上MoS2润滑膜的覆盖面积有关;MoS2润滑膜由大量剥落的MoS2纳米片形成,MoS2纳米片在磨损表面的覆盖面积随着添加量的增加而增加,摩擦表面最外层中的MoS2含量远高于复合材料基体,这是由层状MoS2晶体在摩擦过程中的滑移引起的。(2)研究WS2含量和退火温度对Cu-WS2复合材料组织演变以及力学和摩擦学性能的影响发现,大部分WS2颗粒在700℃和800℃退火后分解,900℃和950℃退火时存在大量的W和Cu2S;WS2的添加对降低Cu-WS2复合材料的摩擦磨损的效果显著,当添加了10 vol%WS2时,Cu基体的摩擦系数从0.76降低至0.2,Cu-40 vol%WS2复合材料的磨损率远小于纯铜;900℃和950℃退火后,Cu-20vol%WS2复合材料的摩擦系数由0.2增加到0.5,700℃退火的复合材料的磨损率最高;摩擦层的严重塑性变形可导致WS2片与滑动方向平行排列,有利于润滑膜的形成和摩擦表面下裂纹的扩展,主要磨损机制是剥层磨损。(3)通过XPS技术深度剖析方法对Cu-MoS2复合材料的磨损表面进行分析。研究发现,MoS2润滑膜在Cu-MoS2复合材料的磨损表面由大量小于200 nm的MoS2薄片组成,从摩擦表面到基体MoS2含量逐渐减小,最外表面MoS2膜的覆盖率为基体的2.9-6.2倍;MoS2膜的覆盖率与MoS2体积含量呈指数关系,这是为何添加过多的润滑剂不会显著降低摩擦系数的原因;通过对薄膜覆盖率的定量表征,成功建立了摩擦系数、润滑膜覆盖率和润滑剂体积分数之间的关系,验证了金属基自润滑复合材料摩擦模型。更多还原

【Abstract】 Copper matrix self-lubricating composites possess good mechanical,physical and chemical properties of metal matrix and excellent tribological properties of solid lubricants,which are suitable for chemical,electrical,high and low temperature,heavy load,high vacuum,strong radiation and so on.Revealling the friction and wear mechanism of copper matrix self-lubricating composites,developing a new method of quantitative characterization of the key features of friction surfaces,and establishing relevant models are the key problems that need to be solved in the design and application of metal-based self-lubricating composites.In this paper,the Cu-Mo2S and Cu-W2S self-lubricating composites were prepared by power metallurgy hot pressing process.the microstructure evolution and friction and wear behavior of the two materials were studied.The friction model of metal matrix self-lubricating composite is established and verified.The details were shown as follows:(1)The effect of MoS2 content on the friction and wear properties of Cu-MoS2 composites was studied.MoS2 was very effective in reducing the friction coefficient of copper matrix composites when the content of MoS2 was less than 20 vol%.When the content of MoS2 is added further,the friction coefficient can hardly be reduced,which is related to the covering area of the MoS2 lubricating film on the worn surface.The MoS2 lubricating film was formed by a large number of peeling MoS2 nanoparticles.The coverage area of MoS2 nanoparticles on the worn surface increased with the increase of MoS2 content,and the content of MoS2 on the outermost surface was much higher than that of the composite material,which was caused by the slip of layered MoS2 crystals during friction.(2)The effects of WS2 content and annealing temperature on microstructure evolution,mechanical and tribological properties of Cu-WS2 composites were investigated.A large number of W and Cu2S appeared in most WS2 particles after annealing at 700℃ and 800℃.The effect of WS2 on reducing the friction and wear of Cu-WS2 composites is remarkable.The friction coefficient of Cu matrix decreases from 0.76 to 0.2 when 10 vol%WS2 is added,and the wear rate of Cu-40 vol%WS2 composites is much lower than that of pure copper.After annealing at 900℃and 950℃,the friction coefficient of Cu-20 vol%WS2 composites increased from 0.2 to 0.5.The wear rate of the composites annealed at 700℃ was the highest.The severe plastic deformation of the friction layer could lead to the parallel arrangement of the WS2 sheets in the sliding direction.It is beneficial to the formation of lubricating film and crack propagation under friction surface,and the main wear mechanism is delamination.(3)The worn surface of Cu-MoS2 composites was analyzed by XPS technique.It was found that the coverage area of MoS2 film on the worn surface of Cu-MoS2 composites decreased from the friction surface to the matrix,which was consisted of a large number of MoS2 thin sheets less than 200nm.The coverage of MoS2 film on the outermost surface is 2.9-6.2 times that of the substrate.The coverage of MoS2 film is exponentially related to the volume content of MoS2.This is why adding too much lubricant does not significantly reduce the friction coefficient.The relationship among friction coefficient,lubricant film coverage and lubricant volume fraction was successfully established,and the friction model of metal matrix self-lubricating composite was verified.更多还原