Study On The Third Body On The Surface Of Brake Disc Material

With the increment of train speed,it has key effects to the safety and comfort of the high-speed trains and the longevity of the brake system that the brake system shows great friction and wear properties in using. The third body,which is created by friction, exists on the surface of the friction pair of the disc braking system.the friction between the disc and pad is changed from the two body friction to the three body friction.the friction and wear properties of the third body decide the using properties and longevity of the braking friction pair.So it makes great sense that we research the third body on surface of the high-speed train’s friction braking material.The friction and wear properties are measured by constant-speed tester,at the friction speed of5880and2930r/min. the friction pressure changes between20N﹑70N﹑100N﹑150N and200N. the research is focused on the micro-morphological characteristics﹑the forming process and the variation of the third body at different friction pressure and different friction speed. Accordingly, the result shows that:The black smooth third body which exists on the surface of the test sample, is a mixture that is made up by the wear debris of the brake disc material and the brake pad material and their oxide.As the micro-morphology, there are lots of raised oxide and adhesive pit in different size, which is full of wear debris. And there are cracks on the surface of the third body and the oxide.Like the process of the nucleation and growth of matal material, the forming process of the third body consist of the phase of nucleation in low temperature﹑the phase of growth and the phase of dynamic balance. As the friction pressure becomes higher, the microhardness of the third body raises.Because the compact degrees of the third body become higher under the higher friction pressure, the wearing quality raises and the abrasion loss gets lower observably.but when the friction pressure is beyond100N, the temperature of the test sample is so high that the intensity of abrasion and oxidation becomes too high, and the abrasion loss gets higher. When the friction pressure is below100N, the abrasion loss decreases as the friction pressure increases because the third body can cover the surface of the test sample symmetrically and compactly. When the friction pressure is beyond100N, the abrasion loss increases as the friction pressure increases because the rate of the creation of the adhesive pit gets higher.