Study On The Effect Of Molybdenum Alloy On The Tribological Behavior Of Cu Based Friction Materials

The two main goals of high-speed train braking materials: one is the requirement with high and stable friction coefficient; the other is a good wear resistance. Material compositions and friction conditions are the key factors to determine the friction and wear property, therefore, to study the effect of the two factors on friction material has an important significance. In this paper, three compositions material(copper-graphite-molybdenum alloy) was prepared by powder metallurgy technology. The effect of molybdenum alloy on friction and wear properties of the material was explored for the first time by friction and wear tests and microstructure analysis. Tribological performance of the material under different conditions was discussed. Main results are shown as follows:1. When the content of Molybdenum alloy is between 0-20 %, with the increase of molybdenum alloy content, the wear resistance and friction coefficient are both increased and tend to stable. The reason is that the high hardness molybdenum alloys play the role of hard particles, which reinforce the softening resistance of the matrix and reduce the extent of plowing.2. When the speed friction was constant, friction and wear performance was influenced by both the pressure and speed. When the speed friction ranges from 200r/min to 1000r/min, with the pressure changes, sharpness and crushing degrees of hard asperity on the friction surface are different, which causes the fluctuations of friction coefficient;3. When the speed friction is instantaneous changed, during the increasing speed process of start speed 0-end speed 3000 r/min, as the speed increases, the temperature rises, the cutting and plowing of the third body intensified, resulting in an unstable friction coefficient; during the reducing speed process of start speed 3000-end speed 0 r/min, the compact third body broken and the surface roughness become higher, which lead to the increase in friction coefficient.4. Compared with dry friction condition, coefficient of friction can be reduced under wet friction condition, while the extent of the reduction is related with the friction speed. When constant speed is 200 r/min, the good lubrication and cooling effect of water causes a difference about 0.35 between the dry and wet friction coefficient. As the speed increases, the high temperature causes the evaporation of water and the centrifugal force promote the water "thrown out" from the friction surface, so the difference between the dry and wet friction coefficient reduce to 0.1.