碳／碳复合材料磨损表面碳结构的激光喇曼光谱分析

采用显微激光喇曼光谱及 X射线衍射考察了基体分别为沥青浸渍碳 /少量气相沉积热解碳和全部气相沉积热解碳的航空刹车用碳 /碳复合材料磨损表面碳结构的变化特征 ,并分析了引起这些变化的原因 .结果表明 ,经过 10次模拟飞机正常着陆刹车试验后 ,相对于石墨化程度各异的磨损次表层炭纤维及基体碳 ,磨损表面各处的石墨化程度及石墨微晶在 a轴方向的尺寸 La趋于均匀 .换言之 ,就复合材料磨损表面拉曼图谱上位于波数 1338.94 cm- 1 的谱峰与15 85 .2 2 cm- 1处的谱峰的积分强度比值 R的倒数 1/ R而言 ,低石墨化程度组元的 1/ R值显著升高 ,而高石墨化程度组元的 1/ R值有所降低 .磨损表面高石墨化程度组元中的石墨微晶通过转动使其 c轴沿磨损表面法线方向择优取向 ,在机械力作用下 ,石墨片层脱离、碎断 ,均匀分布于磨损表面上 .因此 ,在模拟飞机刹车过程中 ,不同结构和密度的 C/ C复合材料磨损表面形成石墨化程度相近的碳结构 ,这是导致复合材料摩擦系数对结构和密度不敏感的重要原因

Laser Raman Micro-spectroscopic Studies of Worn Surface of Carbon/Carbon Composites in Simulated Braking Test of an Aircraft

The worn surfaces of two kinds of carbon/carbon composites after 10 time simulated braking tests of an aircraft were characterized by means of micro Raman spectroscopy and X ray diffraction. The matrix of the composites consists exclusively of pyrolytic carbon or a combination of carbonized pitch and pyrolytic carbon. The structural changes of the carbon on the worn surfaces of the composites were analyzed, and the effect of the structural changes on the friction and wear behavior of the composites discussed as well. As the results, the difference in the graphitization degree of the carbon fibers in the sub worn surface and the matrix becomes indistinctive on the worn surfaces after 10 time simulated braking testing, the size of the microcrystalline graphite along axial a becomes uniform as well. In other words, with respect to the reciprocal of the integral intensity ratio R of the peaks at 1 338.94 cm -1 and 1 585.22 cm -1 in the Raman spectra of the worn composite surfaces, the value of 1/ R for the components of lower graphitization degree increases considerably after the simulated braking test, while that for the components of higher graphitizatino degree decreases to some extent. At the same time, the graphite crystals on the worn surface turn gradually direction until their c axial comes to vertical to the worn surface, and finally the crystals in flake shape cover the worn surface in the presence of normal stress. Subsequently the worn surfaces of almost the same composition and grapgitization degree were generated for the C/C composites of different structures and densities. This accounts for the insensitivity to the structure and density of the friction and wear behavior of the composites.