Powder Metallurgy Fabricated Cu-Fe Based Braking Materials For High Speed Trains

For a large continental country like China, railway transportation is of great importance in the industrialization process and economic development. So far, China has the world’s longest high-speed rail(HSR) network in service as of2011. An increasing requirement for friction materials has to be satisfied in view of the rapid development of the HSR in China. Under such situations, after analyzing and testing the samples imported from abroad, several kinds of braking materials are developed in order to suit such development of the HSR in China.In this paper, based on the analysis on the imported composite braking material samples, the fabrication method is determined to prepare the braking materials with desired performance. Using the powder metallurgy techniques, Fe-Cu based braking materials were prepared. The microstructures and performance of fabricated braking materials were studied in detail.The results show that:(1) the base of imported samples is Cu containing a small amount of Fe. Layered graphite, small amounts of electrode graphite and MoS2were used as lubrication components. The Fe-Cr alloy is used as friction component Friction and wear performance testing results show that:the friction coefficients of such braking materials increase with the rotating speed gradually. The friction coefficient reaches0.42at6800rpm under pressure of0.7MPa. The torque changes with the time smoothly. When the brake pressure is at0.7MPa, the braking time is57s with the calculated braking distance less than3km.(2) Based on the results on foreign samples, we firstly prepared the composite friction braking materials with the Fe-Cr alloy as friction component. We researched the influence of lubrication component, i.e. graphite contents, on the performance of the friction and wear. The results show that the influence of graphite contents on the performance of the friction is not significant. The coefficient of friction decreases gradually with the increase in rotation speed. The friction coefficient reached0.293at6800rpm under0.7MPa. The braking time and braking distance are80s and4km, respectively. The time vs torque curves are smooth too.(3) In order to further improve the friction coefficient, we chose SiC as friction component. The friction coefficient is0.42in6800rpm,0.7MPa. The braking time and braking distance are62s and3.3km, respectively. Though the friction coefficient is comparable with that of the imported sample in value, the coefficient of friction decreased with increasing rotation speeds. The time vs torque curves fluctuate slightly;(4) In order to further improve the properties of fabricated braking materials, we applied heat treatments to Fe-Cr alloy to prepare the harder Fe-Cr alloy, which is used as friction component then. The friction coefficient is0.33at6800rpm under0.7MPa. The braking time and braking distance are65s and3.5km, respectively. At the speed of5000rpm or higher, the friction coefficients increase with the speed. The braking process is smooth. This shows that:changing the friction component properly can improve the friction properties of the composite braking material.