【作者】 董志国；

【导师】 姚广春；

【作者基本信息】 东北大学 ， 有色金属冶金， 2008， 博士

【摘要】 石墨增强铝基复合材料是一种性能优良的自润滑材料,与目前广泛使用的铝锡、铝铅、锡青铜自润滑合金相比,具有优良的耐摩擦性、较高的比强度、较好的环保性,因此有广阔的发展前景。由于石墨颗粒密度较小、与铝熔体润湿性差,目前制备方法主要集中在粉末冶金法和挤压铸造法,存在制件小、成本较高的缺点,液态搅拌铸造法与之相比工艺简单、成本较低廉,越来越受到重视。本文研究了利用搅拌铸造法制备纳米级氧化膜包覆石墨颗粒铝基复合材料技术和其性能。本文首先对石墨颗粒表面包覆氧化物进行了研究,以解决石墨与铝基体之间的润湿性问题,在对不同无机盐水解过程和氧化物对石墨包覆过程机理分析的基础上,研究了硅酸钠、硝酸亚铈、氧氯化锆等无机盐作为前驱体制备氧化硅、氧化铈、氧化锆和氧化铈锆包覆石墨的试验条件,通过测量石墨表面的氧化物含量和高温氧化失重率分析了各种制备条件对包覆效果的影响。研究发现,利用硝酸亚铈水解在石墨颗粒包覆上一层连续的二氧化铈纳米膜,其成核机理为异相非均匀成核,包覆于石墨表面的氧化铈与基体之间形成了C-O-Ce键,具有化学反应的特征。利用正交实验研究了以硝酸亚铈、氧氯化锆为前驱物包覆石墨颗粒工艺,得出氧化铈锆包覆石墨工艺适宜条件为,pH值为6,反应温度为80℃,陈化时间为1h,前驱物浓度为0.2M,石墨粉粒度为50μm。本文在搅拌铸造法制备复合材料工艺中采用真空除气法以降低复合材料的气孔率率,制备出气孔率较低,机械性能较好的复合材料。得到熔体搅拌铸造法制备铝基/氧化物包覆石墨复合材料适宜的主要工艺条件为,搅拌温度：560℃-600℃；搅拌时间：5-8min；搅拌速度：1000-1200r/min;真空炉温度：600℃-630℃；真空度：40kPa-60kPa；真空除气时间：3-5min；采用X射线衍射对复合材料中氧化物包覆石墨颗粒与铝熔体之间的界面进行了研究,表明包覆在石墨表面的氧化硅与铝熔体发生了微弱的反应性润湿,包覆在石墨表面的氧化铈与铝熔体发生了强烈的反应性润湿,包覆在石墨表面的氧化锆与铝熔体发生了微弱的反应性润湿,证明采用氧化铈锆复合包覆既可以与铝熔体发生反应性润湿,改善石墨与铝熔体之间的润湿性,又可以保证石墨不被铝熔体侵蚀。对不同氧化物包覆和不同石墨添加量的铝基/石墨复合材料的抗拉性能、摩擦性能和腐蚀性能进行的检测结果表明,铝基复合材料的抗拉强度、摩擦系数和摩擦磨损量都随石墨含量的增加而逐渐降低,表面包覆氧化铈、氧化锆的石墨铝基复合材料的耐蚀性能优于基体合金和氧化硅包覆石墨铝基复合材料,复合材料的耐蚀性随着石墨含量的增加而下降,石墨的增加提高了点蚀的可能性。摩擦测试结果表明,铝基／氧化物包覆石墨复合材料与基体合金相比,在干摩擦条件下具有良好的自润滑性能,铝基／氧化物包覆石墨复合材料的摩擦系数与摩擦磨损量随石墨的增加而减小,但当石墨超过6%(mass%)时摩擦系数增大。石墨含量为6%(masa%)的复合材料的适用范围为：滑动速度不超过2.6m/s,载荷不超过60N。采用纳米氧化铈锆复合包覆石墨颗粒制备的铝基复合材料,由于氧化铈锆与石墨之间属于化学结合,且氧化铈锆与铝基体之间属于反应性润湿,生成的微量界面化合物有益于提高铝基体的性能,因此所制备的复合材料有较好的力学性能和耐蚀性能。更多还原

【Abstract】 Graphite-particle-reinforced aluminum matrix composite was a good self-lubricating material compared with the Sn-Pb, Cul-Sn, and Al-Pb alloys. It is an environment friendly material with excellent ntifrictional performance and high specific strength, so it can be applied in many fields in the future. But the low density of the graphite particles and the poor wettability with aluminum lead to a main study of fabricated technique focused on the powder metallurgic method and extrusion-casting method. But the obvious shortcomings of these two methods were higher cost and relatively small-scale production. The liquid mechanical stirring technique was paid more and more attention due to its simpler process and lower cost. In this paper, a new graphite-particle-reinforced aluminum matrix composite was fabricated by liquid mechanical stirring technique, in which the graphite was coated by a layer of nano-oxide film, and the basic performance of the composite was systemic studied.To improve the wettability of graphite and molten aluminum, the coating method and mechanism of oxide/graphite were studied firstly. Based on a detailed analysis of the mechanism for oxide coated reaction process and the hydrolyzation process of the inorganic salts, the preparation condition was studied by using the Na2Si03, Ce (NO3) 3 and ZrOCl2 as precursors. The influence of several factors on the characters of oxide/graphite was analyzed by study of the coating ratio and oxidation ratio.By the analysis of oxidation ratio, micrograph of composite particle, it was found out that factors such as pH value, coating temperature, concentration of premonitory matter solution mainly were the dominate factors that affect the coating layer forming. With the optimum parameters, the obtained composite particles had many changes compared with uncoated graphite, such as the decrease oxidation ratio. And a C-O-M bond was confirmed between oxide and the graphite.The preparation process of coated graphite with CeNO3 and ZrOCl2 as precursor was studied with orthogonal experiment. The suitable condition was:pH=6, reaction temperature was 80℃, aging time was 1h, concentration of precursor was 0.2M. particle size of graphite was 50μm.In order to decrease the porosity of the composite material, the vacuum condition was used during the stirring technique process. So material with lower porosity and better mechanical performance could be fabricated. The optimistic processing parameters were:stirring temperature was 560℃-600℃, stirring time was 5-8min, stirring speed was 1000-1200r/min, temperature of the vacuum furnace was 600℃-630℃, degree of vacuum was -0.02 MPa--0.04MPa, time for vacuum was≥3min.XRD was used to investigate the interface of oxide/graphite and the Al-matrix. The results showed a weak reactive wettability between SiO2 and Al, a strong reactive wettability between CeO2 and Al and also a weak reactive wettability between ZrO2 and Al, which proved that two oxides of CeO2 and ZrO2 could improve the wettability between graphite and molten aluminum and during fabrication process without corrosion of graphite by molten aluminum.The wear resistance, tensile strength and corrosive characteristics of the composites materials with different content and kinds of oxide/graphite particle were measured. The result showed that the tensile strength, the friction factor and the weight loss after wearing test descended along with the increase of graphite content. The anti-corrosion performance of CeO2 graphite and ZrO2 graphite reinforced composite materials was higher than that of alloy and SiO2 graphite reinforced composite materials. There showed a decreasing tendency of anti-corrosion performance with the increase of graphite content. The addition of graphite particles improve the possibility of pitting in composite materials.The results of wearing test showed that the oxide/graphite composite materials presented a higher self-lubricating performance comparing with Al alloy. The friction factor and the weight loss descended along with the increase of graphite content. But the friction factor increased when the content exceed 6%.Due to the chemical bond of CeO2/graphite/ZrO2 and reactive wettability with Al matrix, trace compounds were formed in the interface between Al-matrix and oxide. These compounds lead to an improvement of the mechanical and the anti-corrosion performance for the composite materials.更多还原