The Role Of Fe In Copper-based P/M Friction Materials

Copper-based powder metallurgy materials, which are used in the manufacture of braking pad, are constituted by a variety of ingredients, the performance of materials are improved through the regulation and controlling the contents and forms of the material elements. Therefore, studies of the Fe powder in the role of copper-based mechanism, and clear Fe powder's friction and wear Properties for copper-based friction materials are meaningful for developing high-performance brake materials. In addition, China's territory vast, climate variability, the complexity of the railway-operating environment, the friction in these harsh conditions, the materials properties shown by the decision is often the key to product performance. Therefore, the analysis of the harsh conditions for powder metallurgy materials friction and wear performance is guiding significance to improve the performance of brake pad.The copper-based powder metallurgy braking material was fabricated by powder metallurgy, measured by the constant-speed tester, under the speed of 200~3000 r/min, the pressure of 0.5~1.1MPa and the additive water rate of 4.7 ml/min. The results show that:With the increased content of Fe, the wear rate increases, the friction coefficient increases in the low speed, reduced in the high speed. It was because with the increment of iron content, the division of iron in the matrix increase, the wear rate increases. At low speed, materials with high iron content have more hard particles contact the disk, increasing the friction coefficient, and at high speed, the third body on the friction surface of materials with high iron content is denser, reducing the friction coefficient. With iron content of about 5%, the friction materials have the best performance, such as lower wear rates, higher friction coefficient, and steady friction coefficient and wears rate.Compared of water and dry friction, when the braking pressure was small, wear rate under water friction was larger than that of dry friction. It was because when under water friction, the effects of water erosion on the materials accelerated the loss of the third body, results in enhancement of the direct joggle effect between the micro-convex bodies on the friction surface and increase of wears rate. When speed was low, the friction coefficient of dry friction was greater than that of water friction; when speed was high, the friction coefficient of water and dry friction was almost the same. It was because that when the speed was low, for the dry friction, the granular third body increases the joggle level of the micro-convex bodies, and friction coefficient was great. For the water friction, the effect of water erosion on the material surface took away a lot of granular third body, reduced the joggle level and the friction coefficient; when speed was high, water had little influence on the friction surface, so the friction coefficient of wet and dry friction all most the same. With the increasing of brake pressure, friction coefficient increased at low speed and did not change significantly at high speed. It were attributed that at low friction speed, when the brake pressure increased, positive pressure on the wear surface and sub-surface increased, plastic deformation of sub-surface increased. Interaction of the convex-concave peak on grinding surface increased, the actual contact area between the friction disc and SiO2 and Fe increased, the cutting level of increased, the number of hole form by flaking-off increased, and the friction coefficient become greater. Under the conditions of high-speed friction, high brake pressure intensified the effect of surface temperature. With high temperature, the flow lubrication effect of the third body on the surface increased, lead to friction coefficient change smoothly.