【作者】 李娜；

【导师】 邓娟利；

【作者基本信息】 长安大学 ， 材料物理与化学， 2017， 硕士

【摘要】 C/C-SiC刹车材料是最新一代刹车材料,具有低密度、高强度、抗氧化、摩擦系数较高、环境适应性强等优点。已有研究表明C/C-SiC刹车材料磨损率大、刹车不平稳;FeSi75改性C/C-SiC刹车材料,可有效提高材料的抗磨损性能,但在高速高能刹车条件下摩擦系数出现剧烈衰减现象。为了解决FeSi75改性C/C-SiC刹车材料高能载下摩擦系数严重衰减的问题,本文利用刹车材料软硬相匹配的原则,通过改变刹车对偶的材质和对刹车材料进行热处理两种方法来改善FeSi75改性C/C-SiC的摩擦磨损性能。主要研究内容和结果如下:1、研究了FeSi75改性C/C-SiC与C/C-SiC刹车材料互对偶在干态、淡水和海水湿态条件下的摩擦磨损性能和规律。结果表明:(1)在干态条件下,FeSi75改性C/C-SiC与C/C-SiC刹车材料互对偶的摩擦系数大约为0.55±0.02,比FeSi75改性C/C-SiC刹车材料自对偶的摩擦系数提高~83%;FeSi75改性C/C-SiC与C/C-SiC刹车材料互对偶的平均线磨损率(~0.57μm/time)远远低于C/C-SiC刹车材料自对偶(~1.46μm/time);(2)在淡水和海水湿态下,FeSi75改性C/C-SiC与C/C-SiC刹车材料互对偶的摩擦系数几乎无衰减,材料环境适应能力强。2、研究了热处理对FeSi75改性C/C-SiC刹车材料物相与微结构的影响,结果表明:(1)热处理温度从1600°C增加到1700°C,SiC相含量从~18.54 wt%增加到~27.68wt%,Si相含量从~7.02 wt%降低到~4.61 wt%;(2)随热处理温度的升高,孔隙增加,密度减小,SiC晶粒尺寸增大,残余Si含量不再呈大范围聚集分布,而是小范围均匀分布于基体中。3、研究了热处理对FeSi75改性C/C-SiC刹车材料的力学性能的影响,结果表明:随着热处理温度的提高,复合材料弯曲强度从~140 MPa下降到~78 MPa,断裂韧性从~9.0 MPa·m1/2下降到~5.9 MPa·m1/2。4、研究了热处理对FeSi75改性C/C-SiC刹车材料热物理性能的影响规律,表明材料的热膨胀系数、比热容和热扩散系数随热处理温度的提高而下降。5、研究了热处理对FeSi75改性C/C-SiC刹车材料摩擦磨损性能的影响,结果表明:热处理后FeSi75改性C/C-SiC刹车材料中硬质相SiC含量增多、晶粒尺寸增大,使得刹车过程中犁沟效应增强,即提高了材料的摩擦系数,又增加了材料的磨损率。在高速高能刹车条件下摩擦系数从~0.3提高到~0.36,磨损率从~0.36μm/time增加到~0.64μm/time,远小于C/C-SiC刹车材料的磨损率(~1.46μm/time)。更多还原

【Abstract】 Carbon fiber reinforced silicon carbide(C/C-SiC)brake materials have now been the latest generation of brake materials,owing to their excellent properties of low density,high strength,oxidation resistance,high coefficient of friction,and strong environmental adaptability.The available studies have shown that the application field of C/C-SiC is still limited mainly because of higher wear rate and poorer stability of the coefficient of friction(μ).By introducing metallic FeSi2 into C/C-SiC brake composites,FeSi75 modified C/C-SiC brake composites were obtained.The results shown that wear resistance of the FeSi75 modified C/C-SiC brake composites was effectively improved.However,the μ decreased for the introducing of FeSi2,especially under higher braking speed.In order to solve the problem,two methods were proposed to optimize the microstructure and properties of the FeSi75 modified C/C-SiC brake composites.(1)With the principle of combining soft phase with hard phase,the friction and wear properties of FeSi75 modified C/C-SiC and C/C-SiC mutual-mated brakes(FS-SI)were investigated.(2)Heat treatment was conducted on the FeSi75 modified C/C-SiC brake material,and the influences of heat treatment temperature on microstructure,phase,mechanical properties,thermo-physical properties and tribological behaviors were studied.The main conclusions were as the following:1.Tribological properties of FeSi75 modified C/C-SiC and C/C-SiC mutual-mated disks(FS-SI)under dry condition,fresh water and sea water condition were studied.(1)In dry condition,the μ of FS-SI is 0.55±0.02,and it is about 83% higher than that of FeSi75 modified C/C-SiC self-mated disks(FS-FS).The average wear rate of disks in FS-SI is about 0.57 μm/time,which is much lower than that of C/C-SiC self-mated disks(SI-SI)(~1.46 μm/time).(2)The frictional properties of FS-SI in wet condition didn’t faded,which indicated that FS-SI possessed excellent adaptability to the surroundings.2.The influence of heat treatment temperature on microstructure and phase of FeSi75 modified C/C-SiC brake materials:(1)From 1600°C to 1700°C,the content of SiC increased from18.54 wt% to 27.68 wt%,and the content of C decreased from 55.44 wt% to 48.44 wt%;(2)More big pores appeared in the FeSi75 modified C/C-SiC brake materials after heat treatment process,and residual Si phase was no longer gathering distribution but uniform distribution,and the size of SiC particles growing gradually with increasing of the heat treatment temperature.3.The influence of heat treatment temperature on mechanical properties of FeSi75 modified C/C-SiC brake materials: flexural strength of the samples decreased from 140 MPa to 78 MPa with increasing of the heat treatment temperature,and fracture toughness decreased from 9.0 MPa·m1/2 to 5.9 MPa·m1/2.4.The influence of heat treatment temperature on thermo-physical properties of FeSi75 modified C/C-SiC brake materials: the thermal expansion coefficient,thermal capacity and thermal diffusivity declined with increasing of the heat treatment temperature.5.The influence of heat treatment temperature on tribological properties of FeSi75 modified C/C-SiC brake materials: The content of the hard phase of SiC in FeSi75 modified C/C-SiC brake materials increased with the rise of temperature,which enhanced the plough effect and increased the μ during the braking process.The μ of FeSi75 modified C/C-SiC brake material increased from 0.30 to 0.36 under higher braking speed after heat treatment,while the wear rate increased from 0.36 μm/time to 0.64 μm/time,which is still much lower than that of SI-SI(~1.46 μm/time).更多还原