热处理温度对碳纤维增强碳复合材料摩擦学性能的影响

EFFECT OF HEAT TREATMENT TEMPERATURE ON THE TRIBOLOGICAL PROPERTIES OF CARBON FIBER REINFORCED CARBON COMPOSITES

釆用MM-1000型摩擦试验机,对化学气相渗透(chemical vapor infiltration,CVI)并经不同热处理温度制备的碳纤维增强碳(carbon fiber reinforced carbon,C/C)复合材料进行模拟飞机正常降落制动试验。通过扫描电镜对摩擦后的表面及磨屑进行形貌观察;测试了不同热处理温度下样品的硬度和石墨化度,并对摩擦机理进行了初步的分析。结果表明:随热处理温度升高(1600～2600℃),材料的石墨化度升高,硬度降低,磨损减小;摩擦系数先增加后减小,在2200℃左右出现峰值(0.42);刹车时间随摩擦系数增大而缩短,在2200℃处理时,刹车时间最短。C/C复合材料的磨损属磨粒磨损类型,硬质磨粒主要为CVI无定形碳颗粒,摩擦面微观形貌呈现典型犁沟条纹。适当石墨相在磨损过程中由于它的柔软性,增加了摩擦有效接触面积,提高了摩擦系数;过多石墨相的自润滑性,降低了摩擦系数,同时,石墨相改善了材料的耐磨性。

The friction and wear properties of carbon reinforced carbon （C/C） composites prepared by thermal-gradient chemical vapor infiltration and heat treated at different temperatures were investigated on an irltemal MM-1000 dynamometer by simulating the normal brake for landing of an aircraft. The wear surfaces and debris were examined with scanning electron microscopy. The hardness and graphitization degrees of the C/C samples were examined, and the friction mechanisms were analyzed preliminarily. The results indicate that the graphitization degree increases and the hardness decreases with the increase of heat treatment temperature （HTT, 1 600-2 600 ℃）. The friction coefficient increases with the increasing of HTr and reaches the maximum when the HTr is 2 200 ℃; it then decreases, but the wear decreases with the increasing of HTr. Braking stop time is shortened with the increasing of fxiction coefficient and reaches the minimum （0.42） when the HTT is 2 200 ℃. The wear mechanism can be considered as the abrasive particle wear style and a typical canonical pan-furrow marking on the wear surface by hard particles formed from chemical vapor infiltration. The graphite phase enlarges the contact area and increases the friction coefficient by its softness when the proper amount of graphite phase is present, yet self-lubrication when there is excessive graphite phase leads to a reduced fi＇iction coefficient, which can improve the wear resistance of the C/C composites.