Structure And Properties Of C/SiC Friction Material Made By Reactive Melt Infiltration

Due to low density, high service temperature and good abrasivity, C/SiC composite is a new kind of braking materials. Reactive melt infiltration is the most promising way to manufacture C/SiC braking material with low cost. In this paper, short fiber preform C/SiC braking materials are manufactured by RMI and C cloth lamination and needle-punched felt perform are contrasts to short fiber perform. Effects of different processing parameters on structure and properties C/SiC braking material are discussed. The results are as follows:(1) C/SiC braking materials with low porosity are manufactured. open porosity is between 3.4% —4.8%, and bulk density is between 1.82—2.26 g/cm3.(2) Two kinds of drawbacks of C/SiC braking material are studied. Due to lots of NH3 emission in hot pressing stage, pores with different sizes are created in samples. In RMI prosessing stage, cracks are possibly created because of some factors especially 8.1% volume expansion of liquid Si during freezing.(3) Mechnical properties of short fiber reinforced C/SiC material made by RMI are tested. Compressive strengths are between 107-257 MPa. Flexual strengths are between 56—86MPa. Interlaminar shear strengths are between 21—35MPa. Tensile strength is 26MPa. Requirements of mechnical properties during braking of aircraft are met. C/SiC samples do not suffer a rupture after many simulation braking tests and can resist huge thermal shock during braking.(4) The thermal diffusivity of C/SiC braking materials is investigated. Thermal diffusivity decreases when temperature increases. Axial Thermal diffusivity of short fiber and 2D fabric is twice as large as longitude thermal diffusivity. The thermal diffusivity of high density C felt (0.34 cm~2/s at room temperature) is the highest andconsiderably higher than that of the low density C felt (0.1 cm~2/s at room temperature). Graphitation and SiC filler have obvious effects on thermal diffusivity of short fiber perform C/SiC braking materials.(5) Friction property and wear property of C/SiC friction material are investigated. Coefficient of friction (COF) and its stability decrease in various range when force or energy increase. Graphitation before Si infiltration can improve friction property inmmensly when COF increases from 0.26 to 0.37 and stability of COF increases from 0.46 to 0.56. SiC filler has little inpact on friction property but obvious effect on wear property. SiC filler can increase wear of C/SiC material. Friction property can be affected by different preform C/SiC materials. The stability of coefficient of friction of C cloth lamination preform C/SiC material is interior to that of short fiber C/SiC material.