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摘要: 閘片是高速列車制動系統的核心部件，本文設計了350 km·h–1高速列車用銅基閘片材料，對閘片進行了1∶1臺架實驗考核，重點分析了摩擦膜的性質及閘片的摩擦磨損性能。結果表明，研制閘片不僅具有優異的摩擦系數穩定性和低的磨耗，還具有不傷盤的特點。瞬時摩擦系數和平均摩擦系數均滿足TJCL/307—2019標準的要求，摩擦系數穩定性為0.0015，250～380 km?h–1制動速率范圍內的摩擦系數熱衰退僅0.027，在380 km?h–1下的平均摩擦系數仍維持在0.35，平均磨耗僅0.06 cm3?MJ–1。閘片優異的摩擦制動性能歸因于形成了高強韌、低轉移速率的摩擦膜。利用大粒徑摩擦組元作為外部運動障礙釘扎摩擦膜。摩擦膜中的亞微米磨屑作為摩擦膜與對偶盤的嚙合點，提供摩擦阻力，以保持高速制動時的摩擦系數。添加的易氧化組元為摩擦膜源源不斷提供氧化物，研磨生成的納米氧化物作為彌散相強化摩擦膜。通過多尺度顆粒的協同增強，實現了摩擦膜的動態穩定化，賦予了閘片優異的摩擦磨損性能。Abstract: The brake pad is the key component in the braking system of high-speed railway trains. The running speeds of commercial high-speed railway trains in China can reach higher than 350 km·h?1. The friction coefficient of brake pads is a key factor determining the safety of any vehicle brake, and a high and stable friction coefficient is ideal for ensuring the safety of the braking system. In practical applications, the friction coefficient can vary because of the changes in the working conditions, such as sliding speed, braking pressure, and temperature between contact surfaces. Under severe conditions, such as high-speed braking and overload, the friction coefficient decreases markedly, which lengthens the braking distance and braking time. Based on the friction performance collaborative regulation theory of powder metallurgy friction materials, a Cu-based friction material was designed. The performance of the brake pad was tested on the full-scale dynamometer, and the characteristics of the friction film were analyzed in detail. Results show that the brake pad exhibits high stability of the friction coefficient, low wear loss, and the capability to protect the brake disc. Both the instantaneous friction coefficient and average friction coefficient of the developed brake pad meet the requirements of the TJ/CL307—2019 technical condition. The stability of the friction coefficient is 0.0015. The recession of the friction coefficient from 250 to 380 km·h?1 is as low as 0.027. The average friction coefficient at 380 km·h?1 remains at the relatively high value of 0.35, and the average wear loss is only 0.06 cm3·MJ?1. The excellent friction and braking performance of brake pads can be attributed to the formation of friction films with high strength and toughness and low transfer rate. The friction components with large particle sizes are used as external motion obstacles to nail the friction film. The submicron wear debris in the friction film serves as the meshing point between the friction film and the dual disc to provide friction resistance, thus maintaining the friction coefficient during high-speed braking. Oxides are continuously supplied by adding easily oxidized components, and the nanosized oxides generated by the severe grinding process are used in the dispersion-strengthening phase. The multiscale particles synergistically enhance the dynamic stability of the friction film. The metal oxide layer on the friction surface reduces and stabilizes the friction coefficient and enhances the wear resistance because it prevents metal–metal contact between the brake pad and the brake disc. The fade phenomenon that occurs under high braking speed and overload conditions is effectively prevented.
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圖 2 美國Link 3600型1∶1制動臺架.（a）整體形貌；（b）慣量系統；（3）制動盤；（d）實驗過程中制動盤狀態
Figure 2. Full-scale dynamometer (Link 3600, US): (a) overall morphology; (b) inertia system; (c) brake disc; (d) morphology of the brake disc during the test
圖 3 不同制動速度下的瞬時摩擦系數和制動壓力.(a)200 km?h–1；(b)250 km?h–1；(c)300 km?h–1；(d)350 km?h–1；(e)380 km?h–1
Figure 3. Instantaneous friction coefficient and braking force under different braking speeds: (a) 200 km·h?1; (b) 250 km·h?1; (c) 300 km·h?1; (d) 350 km·h?1; (e) 380 km·h?1
圖 4 1∶1臺架實驗的平均摩擦系數.（a）干燥條件；（b）潮濕條件
Figure 4. Average friction coefficient from full-scale dynamometer under different conditions: (a) dry; (b) wet
圖 5 在80 km·h–1下，以30 kW在壓力32 kN下持續制動20 min的瞬時摩擦系數和溫度的變化
Figure 5. Variations of instantaneous friction coefficient and temperature during the continuous 20 min braking with the power of 30 kW, braking force of 32 kN, and braking speed of 80 km·h?1
圖 6 1∶1臺架實驗前(a)后(b)閘片的形貌
Figure 6. Morphology of the brake pad before (a) and after (b) the braking test on the full-scale dynamometer
圖 7 1∶1臺架實驗前后制動盤的形貌.(a)實驗前;(b)實驗后
Figure 7. Morphology of the brake disc: (a) before the test; (b) after the test on the full-scale dynamometer
圖 8 磨損表面在LSCM下的形貌，相應的三維形貌和高度分析.(a1～a3)具有大面積摩擦膜覆蓋的區域;(b1～b3)發生剝離磨損的區域
Figure 8. LSCM images of the worn surface, 3D morphologies, and corresponding height analysis: (a1–a3) regions covered by the large-scale friction film; (b1–b3) wear regions
圖 9 摩擦膜的BSE形貌(a,b)以及圖(b)中相應的元素面分布分析.(c) Cu; (d) Si; (e) Fe; (f) Cr
Figure 9. BSE images of the friction film (a,b) and element mapping in (b): (c) Cu; (d) Si; (e) Fe; (f) Cr
圖 10 摩擦表面橫截面的BSE顯微組織
Figure 10. BSE images of the cross-section of the friction surface
圖 11 表層摩擦膜中納米相的TEM形貌.(a)氧化物顆粒形貌；(b)氧化物的高分辨TEM（HRTEM）顯微組織；（c）石墨形貌；（d）粒徑不同的氧化物顆粒
Figure 11. TEM images of nanoparticles in the friction film: (a) image of oxide particles; (b) HRTEM image of oxide particles; (c) image of graphite; (d) oxide particles with different particle sizes
表 1 銅基閘片材料的成分及各組元粒徑
Table 1. Chemical compositions of Cu-based friction materials and size of the components
Component Mass fraction/% Particle size/μm Cu 44–52 48–75 Fe 16–26 45–150 CrFe 1–5 30–80 Cr 1–5 30–80 Graphite 5–10 150–400 SiO2 1–5 10–40 Others 1–5 — 
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表 2 閘片的力學性能及1∶1臺架試驗數據
Table 2. Mechanical properties of brake pads and test data from the full-scale dynamometer
Performance criteria Prepared brake pads Density/(g·cm–3) 5.04 Hardness(HB) 17 Shear strength of friction body/MPa 16 Shear strength of bonding surface/MPa 25 Compressive strength of friction body/MPa 130 Instantaneous friction coefficient, μa Meet the tolerance requirements of instantaneous friction coefficient Mean friction coefficient, μm Meet the tolerance requirements of the mean friction coefficient Mean wear loss/(cm3·MJ–1) 0.06 Temperature distribution of the brake disc Uniform distribution Stability of μa (50–250 km·h–1) 0.021 Stability of μa (300 km·h–1) 0.0074 Stability of μa (350 km·h–1) 0.0127 Stability of μa (380 km·h–1) 0.0015 Fading of μa (250–380 km·h–1) 0.027 Braking distance, m (braking at 380 km·h–1 and the maximum clamping force) 7018
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