3D Network SiC-metals Composites for Heavy Duty Brake Applications

Abstract

A critical component of high-speed trains is their braking systems. A key technology of a braking system is the braking material. Its primary function is to dissipate mechanical energy by converting it into heat during the braking process without experiencing damages in structure and deterioration in property. Currently, the most commonly used brake materials for high-speed trains of 200~300 km/hour are copper matrix powder metallurgy materials composed by base metal Cu, Sn and Zn and additives Fe, Ni, Mo and graphite (Desplanques et al., 2001). These materials have various advantages such as stable friction coefficient, lower noise compared to iron shoe materials, high thermal conductivity and well running-in characteristic (Zhang et al., 2010) and (Wahlstrom et al., 2010). However, with increasing the speed to 380 km/hour, these materials suffer from several problems including adhesion, over abrasion, fatigue fracture and flake spalling. These materials become inadequate to withstand 30 MJ of braking energy during the braking process in emergency situations (Guerin et al., 1997). Therefore, it is necessary to develop new brake materials of improved performances. The development of these materials is critical for the success of the technology of high-speed trains. The success of the project is of high technical significance. To meet the request for brake material application for speeds above 350 km/hour, main properties of the brake material need to satisfy the following requirements (Tirovic et al., 2001): 1. Heat capacity above 500 J/kg.K; 2. Thermal conductivity above 45 W/m·K; 3. Crushing strength above 280 MPa; 4. Bending strength above 70 MPa; 5. Average friction coefficient 0.35 and the vibration below 20%; 6. Abrasion below 210-3 cm3/MJ·cm2; 7. Withstand heat energy above 30 MJ during braking. The current copper matrix braking materials are able to meet all the above except requirements (1) and (7). Their heat capacities are 390 J/kg.K. Moreover, they cannot dissipate 30 MJ. Generally, at 22 MJ, their surface temperature may reach 1100°C, above the melting point of copper (Bauer&Li, 2005). To solve the problem, an option is to introduce second phase materials of high melting points and high heat capacities into the copper