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摘要: Cu基粉末冶金闸片在高速制动时受温度的影响易发生摩擦系数的衰退，直接影响列车制动的有效性。利用1:1制动试验台进行不同速度下Cu基粉末冶金闸片的高速制动试验，分析试验后的摩擦材料和磨屑组织。结果表明：制动速度为350 km·h−1和380 km·h−1产生的高温使摩擦材料表层的金属基体发生软化熔融，降低了摩擦副表面微凸点的剪切阻力，导致摩擦系数下降。摩擦表面形成的金属氧化膜具有减磨作用，造成摩擦系数的进一步衰退。在380 km·h−1制动时，石墨在高温下被氧化，摩擦表面失去稳定的润滑膜，出现粘着磨损和材料转移，磨耗量大幅增加。Abstract: Friction coefficients of the Cu-based powder metallurgical brake pads decline due to the high temperature during the high-speed braking, which will directly affect the train braking effectiveness. The 1:1 high-speed braking tests of Cu-based powder metallurgical brake pads were carried out under the different speeds, and the friction materials and abrasive texture after the tests were analyzed. The results show that, the metal matrix on the surface of friction materials melts due to the high temperature under the braking speeds of 350 km·h−1 and 380 km·h−1, decreases the shear resistance of the micro bumps on the friction surface, and causes the decline of friction coefficient. The metal oxide films formed on the friction surface reduce the wear, resulting in the further decline of friction coefficient. The friction surface lost the stable lubricant film when the graphite is oxidized under the high temperature generated by 380 km·h−1 braking, and the wear loss increases significantly due to the adhesive wear and material transfer behavior.
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Key words:
- Cu-based powder metallurgy brake pads /
- friction materials /
- wear loss /
- high speed braking /
- fading
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图 2 平均摩擦系数随制动速度的变化
Figure 2. Variation of the average friction coefficient with the braking speed
图 4 不同制动速度制动后摩擦材料外观形貌：（a）120 km·h−1；（b）300 km·h−1；（c）350 km·h−1；（d）380 km·h−1
Figure 4. Profiles of the friction materials after braking at different braking speeds: (a) 120 km·h−1; (b) 300 km·h−1; (c) 350 km·h−1; (d) 380 km·h−1
图 5 不同制动速度制动后磨屑扫描电子显微形貌：（a）120 km·h−1；（b）300 km·h−1；（c）350 km·h−1；（d）380 km·h−1
Figure 5. SEM images of the abrasive after braking at different braking speeds: (a) 120 km·h−1; (b) 300 km·h−1; (c) 350 km·h−1; (d) 380 km·h−1
图 6 图5磨屑形貌放大图：（a）120 km·h−1；（b）300 km·h−1；（c）350 km·h−1；（d）380 km·h−1
Figure 6. Enlarged images of the abrasive in Fig.5: (a) 120 km·h−1; (b) 300 km·h−1; (c) 350 km·h−1; (d) 380 km·h−1
图 7 不同制动速度制动后磨屑断面显微组织：（a）300 km·h−1；（b）350 km·h−1；（c）、（d）380 km·h−1
Figure 7. SEM images of the abrasive fracture surface: (a) 300 km·h−1; (b) 350 km·h−1; (c), (d) 380 km·h−1
图 8 380 km·h−1制动后的摩擦表面形貌：（a）边缘；（b）中部；（c）横截面；（d）制动盘表面
Figure 8. SEM images of the wear surface after 380 km·h−1 braking: (a) the edge; (b) the center; (c) the cross-section; (d) the brake disc surface
图 9 图8（b）视场元素分布：（a）C；（b）O；（c）Fe；（d）Cu
Figure 9. Element distribution of Fig.8(b): (a) C; (b) O; (c) Fe; (d) Cu
图 10 摩擦材料初始表面元素分布：（a）C；（b）O；（c）Fe；（d）Cu
Figure 10. Element distribution of the original surface: (a) C; (b) O; (c) Fe; (d) Cu
表 1 制动摩擦试验方案
Table 1. Scheme of the brake friction test
制动次序 制动速度 / (km·h−1) 双侧闸片压力 / kN 初始温度 / ℃ 备注 1～3 120 30 50～60 第3闸结束后闸片称重，收集磨屑 4～6 300 30 50～60 第6闸结束后闸片称重，收集磨屑 7～9 350 30 50～60 第9闸结束后闸片称重，收集磨屑 10～12 380 30 50～60 第12闸结束后闸片称重，收集磨屑 
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表 2 摩擦材料的物理和力学性能
Table 2. Physical and mechanical properties of the friction materials
硬度，HBW 密度 / (g·cm−3) 摩擦体剪切强度 / MPa 摩擦体与粘接面剪切强度 / MPa 摩擦体抗压强度 / MPa 16 4.6 10 13 93
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表 3 图6中不同位置磨屑能谱分析
Table 3. EDS analysis of abrasive in Fig.6
位置 质量分数 / % C O Cr Fe Cu 位置1 14.19 18.98 5.49 21.33 39.41 位置2 16.95 14.96 4.07 22.75 33.52 位置3 5.17 16.95 1.10 5.26 70.96 位置4 3.60 13.94 — 5.11 77.35
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