Design, Preparation And Tribological Properties Of Copper Matrix Powder Metallurgy Composites For Brake Pads Of High-speed Train

With the rapid development of high-speed trains in China,the safety of trains in operation is gradually being concerned.The friction material for high-speed train brake pads is the core component of the high-speed train braking system,which plays a crucial role in the process of emergency braking,and its performance directly affects the speed,safety and stability of the braking process.It is the core components of high-speed train braking systems.However,most of China's high-speed rail brake pad materials rely on imports.Therefore,in-depth research on copper-based friction materials for high-speed train braking is of great significance to the development of China's high-speed train braking technology and the improvement of economic benefits.This paper takes copper-based powder metallurgical friction materials for high-speed train brake pads as the research object.Through the design of composite materials and the matching between different added components,the interface between the added components and the matrix is optimized and the relationship between the added components and the tribological properties of composite materials and the tribological mechanism are studied to provide a theoretical basis for the preparation,performance improvement and practical production application of brake pads for high-speed trains in China.Using powder metallurgy technology to prepare copper-based powder metallurgical friction materials with different compositions,observe the structure and structure of the composite materials,test the physical,mechanical and friction and wear properties of the composite materials,and discuss the tribological mechanism of the composite materials.The main innovations and main conclusions of this paper are as follows:?1?Select SiO₂ as the hard phase in the composite material,electroless plating was used to plate copper on the surface of the SiO₂ particles to improve the interface wettability between the SiO₂ particles and the copper matrix.The results show that,copper plating on the surface of silica can effectively reduce the pores at the interface of SiO₂ particles and the copper matrix and improve the bonding strength of the interface of SiO₂ particles with the copper matrix,thereby improving the density and hardness of the composite;The addition of SiO₂ particles can increase the friction coefficient and wear resistance of the composite,electroless copper plating on the surface of SiO₂ particles can further improve the friction stability,friction coefficient and wear resist of the material;The main wear mechanism of composites without SiO₂ particles in the friction process is severe adhesive wear and delamination Wear,the addition of SiO₂ particles can reduce the adhesion wear and delamination wear of composite material.The wear mechanism of copper-plated composite materials on the surface of SiO₂ particles is slight adhesion wear and delamination wear.?2?The chemical treatment method is used to increase the distance between the flake graphite layers,and the copper is deposited on the flake graphite surface and between the layers by chemical plating.The copper-coated flake graphite structure with sandwich structure is successfully prepared.Effectively improving the bonding strength of graphite and matrix and the mechanical properties of the composite material.Compared with the samples with flake graphite and copper-plated flake graphite,the copper-coated flake graphite composite material with sandwich structure has the highest friction coefficient ang the lowest wear rate;With the increase of flake graphite content,the physical and mechanical properties of the material decrease,and the friction coefficient of the material also decreases,but the wear resistance of the material is improved.The copper-coated flake graphite composite material with 10wt.%Sandwich sandwich structure has the best tribological properties.?3?Use CrFe alloy particles instead of traditional large-sized ceramic particles to reinforce copper-based composite materials.The results show that the CrFe particles have a good interface bonding with the copper matrix.The hardness of the material increases first and then decreases with the increase of the content of CrFe particles.The material has the highest Brinell hardness?33.4 HBW?when the mass fraction of CrFe particles is 8wt%.The addition of CrFe particles can stabilize the wear rate and friction coefficient of the material.The reason is that during the friction experiment,CrFe alloy particles can limit the plastic deformation of the material surface.The material wear method without adding CrFe particles is mainly delamination wear.The addition of CrFe particles can reduce the delamination wear of the material,but excessive CrFe particles will cause serious abrasive wear.When the content of CrFe particles is 8 wt.%,The material has the most stable friction coefficient and the lowest wear rate.?4?SiO₂ particles?10-20?m?were selected as small-size hard particles,and CrFe particles?average particle size 200?m?were used as large-size hard particles to prepare double-sized hard particles reinforced copper matrix composites.The results show that hard particles of different sizes play different roles in the friction and wear properties of composite materials.The main function of the small size hard particles is to improve the friction coefficient and strengthen the matrix.The large size hard particles mainly serve as a skeleton to prevent the deformation of the matrix and stabilize the friction coefficient and wear rate.The composite material with small size hard particles and large size hard particles added at the same time has more excellent tribological properties than the material with single size hard particles.?5?Copper matrix composites reinforced with molybdenum disulfide were prepared by sintering at different temperatures.The results show that the hardness and compressive strength of the material increase with the increase of the sintering temperature,the friction coefficient of the material increases with the increase of the sintering temperature,and the wear rate decreases with the increase of the sintering temperature.When the sintering temperature is 920?,the material has the best tribological properties.When the sintering temperature is 720?,the wear mode of the material is severe abrasive wear.When the sintering temperature is 920?,the wear mode of the material changes from severe abrasive wear to slight adhesive wear.