Properties Optimization Of FeSi75 Modified C/C-SiC Brake Composites

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(?).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 ? 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 ? 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 ?m/time,which is much lower than that of C/C-SiC self-mated disks(SI-SI)(~1.46 ?m/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 ? during the braking process.The ? 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 ?m/time to 0.64 ?m/time,which is still much lower than that of SI-SI(~1.46 ?m/time).