Effect of Cu‒Fe pre-alloyed powders on the friction and wear properties of Cu-based friction materials
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摘要: 利用粉末冶金方法制备了含不同质量分数铜铁预合金粉末的铜基摩擦材料，并在不同温度下对材料摩擦性能进行测试。结果表明：铜铁预合金粉末的引入使得铁元素在烧结后铜基体中及铜基体与其他组元界面处析出，阻碍了烧结，导致材料密度下降。存在于界面处的铁以及反应生成的珠光体成为硬质强化相，使得材料的磨损机理从纯铜基体时的黏着磨损向添加铜铁预合金粉末之后的磨粒磨损转变，导致摩擦系数先下降后上升。200～250 ℃为摩擦系数保持稳定的临界温度。当超过临界温度时，摩擦表面铜软化，其自润滑作用使得摩擦系数下降。含30%铜铁预合金粉末的铜基摩擦材料（质量分数）的摩擦磨损性能最佳，这是由于此时摩擦材料兼具铜良好的塑性以及生成的适量硬质相能够强化摩擦表面。Abstract: Copper-based friction materials containing the Cu‒Fe pre-alloyed powders in different mass fraction were prepared by powder metallurgy method, and the friction properties were tested at different temperatures. The results show that, with the introduction of the Cu‒Fe pre-alloyed powders, the iron participates in the copper matrix and the interface between copper matrix and other components, which hinders the sintering process and reduces the density. The formed pearlite and the participated iron at the interface act as the hard-strengthening phase, which changes the wear mechanism from the adhesive wear of the pure copper matrix to the abrasive wear after adding the Cu‒Fe pre-alloyed powders, resulting in the reduction of friction coefficient at first and then rising. The critical temperature is 200～250 ℃ for maintaining the stable friction coefficient. When the temperature exceeds the critical temperature, the copper on the friction surface softens and its self-lubricating effect leads to the decrease of friction coefficient. 30% Cu‒Fe pre-alloyed powders by mass is the optimum content for the copper-based friction materials, and the copper-based friction materials have the good plasticity of copper and the appropriate amount of the hard phases to strengthen the friction surface.
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图 1 电解铜粉（a）和铜铁预合金粉末（b）显微形貌
Figure 1. Morphology of the electrolytic copper powders (a) and the copper‒iron pre-alloyed powders (b)
图 3 铜铁预合金粉末基体和CF55试样中铁元素的析出：（a）铜铁预合金粉末基体烧结残留界面上铁元素的析出形貌；（b）透射电镜暗场像下铜铁预合金粉末基体中弥散析出的富铁颗粒；（c）CF55试样中铁沿铜基体‒SiO2界面析出；（d）CF55试样中铁元素以珠光体的形式沿铜基体-石墨界面析出
Figure 3. Iron precipitation in the Cu‒Fe pre-alloyed powder matrix and the sample CF55: (a) precipitation image of Fe element in the residual interface of the Cu‒Fe pre-alloyed powder matrix during sintering; (b) dispersive precipitation of the iron-rich particles in Cu‒Fe pre-alloyed powder matrix in the TEM dark field image; (c) precipitation image of Fe element along the Cu‒SiO2 interface of the sample CF55; (d) precipitation image of Fe element as pearlite along the Cu‒graphite interface of the sample CF55
图 4 不同样品平均摩擦系数随温度的变化
Figure 4. Mean friction coefficient with temperature of the samples
图 5 瞬时摩擦系数：（a）200 ℃；（b）350 ℃；（c）350～100 ℃降温阶段
Figure 5. Instantaneous friction coefficient at the different temperature: (a) 200 ℃; (b) 350 ℃; (c) the cooling stage of 350~100 ℃
图 7 激光共聚焦显微镜下不同样品的摩擦表面：（a）CF0；（b）CF20；（c）CF30；（d）CF55
Figure 7. Friction surface of the different samples under the confocal laser microscope: (a) CF0; (b) CF20; (c) CF30; (d) CF55
图 8 不同试样摩擦表面摩擦膜覆盖区域的显微形貌：（a）CF0；（b）CF15；（c）CF30；（d）CF55
Figure 8. SEM images of the friction surfaces covered by friction film of the different samples: (a) CF0; (b) CF15; (c) CF30; (d) CF55
图 9 CF55破碎界面处的显微形貌及能谱分析：（a）破碎界面处的显微形貌；（b）界面内储存磨屑的能谱分析
Figure 9. SEM images and EDS analysis of the CF55 broken interface: (a) SEM images of the CF55 broken interface; (b) EDS analysis of the wear debris stored in the interface
表 1 铜基摩擦材料化学成分（质量分数）
Table 1. Chemical composition of the prepared copper-basedfriction materials
% 试样编号 Cu Cu‒Fe Sn 石墨 SiO2 莫来石 Fe 余量 CF0 55 0 5 14 5 9 7 5 CF15 36 20 5 14 5 9 6 5 CF30 26.5 30 5 14 5 9 5.5 5 CF55 2.75 55 5 14 5 9 4.25 5 
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表 2 图8（a）中A区域能谱分析（原子数分数）
Table 2. Energy spectrum analysis of area A in Fig.8(a)
% O Cu Fe Al Si Sn Ni 29.34 34.14 23.94 2.68 4.69 1.61 3.59
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