【作者】 刘学然；

【导师】 刘勇兵； El-Ghannam；

【作者基本信息】 吉林大学 ， 材料学， 2008， 博士

【摘要】 纳米功能复合材料是纳米科技的重要研究领域之一。本文采用新型粉末冶金技术制备了具有自润滑功能的纳米铜/碳复合材料和具有生物活性功能的纳米氧化硅/磷酸钙复合材料。Cu-C不互溶体系机械合金化24h后,Cu和C实现了原子级的混合,Cu-4%C粉末形成了纳米结构的过饱和固溶体,但是,Cu-6%C和Cu-8%C粉末中还有少量的残余碳,以非晶态碳和层片状石墨形式存在。XPS研究表明,除了少量的碳形成了氧化物及铜碳间隙固溶体外,大部分碳以单质形式固溶在位错、晶界等缺陷处,故为亚固溶。冷压成型和放电等离子烧结后铜/碳复合材料仍保持着纳米结构,SPS烧结样品中Cu-C键的数量明显增加,Cu-C界面干净,结合良好。形成过饱和固溶体的铜/碳复合材料表现出更好的减摩耐磨性能,使从轻微磨损向严重磨损的转折点从机械混合冷压样品的100N提高到140N。在磨损过程中,铜/碳复合材料以挤出-涂抹-机械混合的机制形成表面富石墨的润滑膜,Cu-4%C在140N,Cu-8%C在100N载荷时磨损表面形成的润滑膜最完整,显著提高了铜/碳复合材料的摩擦磨损性能。氧化硅/磷酸钙复合材料(SCPC)主要由β-NaCaPO4和α-cristobalite晶相组成,在低的压力或温度下,晶粒尺寸在纳米级。随着压力和烧结温度增加,材料的孔隙率、晶粒尺寸和SiO2熔化相百分含量明显增加,导致SCPC的力学性能显著降低。压缩试验表明:纳米SCPC具有优异的抗压强度(105.62~246.64MPa)和弹性模量(9.49~14.07GPa),相当于密质骨的力学性能。更多还原

【Abstract】 Material, energy and information are three mainstays of the modern science and technology. New materials continually appear and develop towards the composite, high functional or intelligentized direction. Hence, functional nano-composites have been attracting much attention due to their particular properties and new laws, such as nanosized materials, amorphous materials, magnetic materials, superconductive materials, self-lubricating materials, and biomaterials. Self-lubricating metal matrix composites not only have mechanical properties of metal matrix, but also have good tribological properties of solid lubricant. Biomaterials have been used as the graft substitutes or regeneration. The powder metallurgy technology is used to prepare the functional nano-composites because it has the ability of controlling the composition and microstructure of the material in the wide range and taking shape. Powder metallurgy technology gives the new method and thought of developing new functional composites.Cu/C composites are a kind of the metal matrix composites combining both structural and functional properties, which have been paid great attention due to combinations of high strength, conductivity, thermal conductivity, and excellent wear resistance. Cu/C composites are always the priority materials for the electric contact and brush. But, the interface between C and Cu is not almost wettable and exists in the form of mechanical bonding. This kind of low bonding strength often leads to the enforcement pulling out and falling out. In general, the matrix alloyed or carbon enforcement surface processed is used to improve the wettability between Cu matrix and carbon enforcement, but the effect is not evident. Therefore, the improvement of strength, hardness and wear resistance has been the central task for the research and development of Cu/C materials.In this work, mechanical alloying (MA) of mixtures of copper and graphite were performed in a high-energy ball mill, and Cu/C nano-composites were fabricated by cold press process and spark plasma sintering (SPS), respectively. The microstructure, Cu-C interface, phase composition, properties, frication and wear characteristics were studied, which will lay a solid foundation for the development of novel low-friction and anti-wearing Cu/C self-lubricating nano-composites.Copper powders with 2, 4, 6, and 8 wt.% C were mechanical alloyed for various times to obtain the nanostructurally supersaturated solid solution of carbon in copper. The investigations indicate that in the Cu-C immiscible system, copper and graphite powders form the samdwich, and nanocrystalline, amorphous, and supersaturated solid solution appear during milling. After milling for 24 h, Cu-4%C powders form the nanostructurally supersaturated solid solution of carbon in copper. Whereas, there are a few residual carbon atoms in the form of amorphous carbon and lamellar graphite for Cu-6%C and Cu-8%C powders except for the formation of nanostructural solid solution. XPS study reveals that the solid solution of carbon in copper is formed at atomic level during milling. However, it is obvious that most of carbon atoms can locate in graphite regions, namely, segregated in the interfaces and dislocations to form sub-solid solution. Therefore, a high-energy ball mill can largely extend the solid solubility of carbon in copper and 4% C is dissolved in Cu. It is ascribed to the decrease of the grain size and increase of the lattice strain.The microstructures of cold-pressed and SPS sintered Cu/C composites keep the nanostructure. It is noted that the carbon particles and strips exist in the interior of copper particles, the interface or pore. In comparison with cold-pressed compacts, the number of the Cu-C boud of SPS compacts increases obviously. Some Cu twins in the width of 20 nm and good Cu-C interface binding are found. A double activation mechanism for the consolidation of Cu/C composites in the MA-SPS processing is proposed, which improves the sintering activity of Cu/C powders. Dense Cu/C nano-composites are able to be obtained by SPS sintering at 600℃for 3 min.Cu-4%C compact sintered at 600℃has the relative density of 98%, which is rather high than that of cold-pressed compact of 87% with the same carbon content. On the other hand, the microhardness of SPS compacts is rather high than that of cold-pressed compacts. The cold-pressed compacts for Cu-2%C have a maximum value of 122 HV, and the SPS compacts reach a maximum value of 239 HV.Tribological properties of Cu/C nano-composites forming supersaturated solid solution were investigated. The results reveal that the Cu/C composites prepared by different processing show better wear resistance than pure Cu, and tribological properties of Cu/C composites forming supersaturated solid solution are better than the Cu/C mechanically mixed for 1h, which results in the turning point from the light wear to heavy wear increasing from 100N for mechnical mixing to 140 N for mechanical alloying. MA-SPS samples have the best wear resistance. For Cu-4%C nano-composites at the load of 140 N and Cu-8%C at 100 N, the worn surface forms an entire lubricative film with rich-in graphite. Therefore, the friction coefficient and wear rate decrease considerably.Salica-calcium phosphate composite (SCPC) was fabricated by the powder metallurgy technology. The microstructure, morphology, phase compositions, and mechanical properties were studied. The results show that SCPC is mainly made ofβ-NaCaPO4 andα-cristobalite crystalline phases. Under low compact pressure or sintering temperature, SCPC grains are nanosized. A melting phase appears under high compact pressure or sintering temperature. In addition, the percent of the melting phase increases significantly with the compact pressure or sintering temperature. SEM-EDX and TEM-EDX reveal the melting phase is a SiO2 amorphous phase. The increase of compact pressure or sintering temperature leads to the increase in the porosity, grain and the percent of the melting phase, which causes the decrease of the mechanical properties of SCPC. Compressive test indicates that SCPC nano-composites have the superior compressive strength of 105.62~246.64MPa and modulus of elasticity of 9.49~14.07GPa, which are comparable to the reported values for cortical bone.更多还原