【作者】 余海峰；

【导师】 马学鸣；

【作者基本信息】 上海大学 ， 材料学， 2005， 博士

【摘要】 基于纳米材料诱人的特性和应用前景,本论文首次将纳米技术应用在AgC触头材料的制备中,研制出性能优异的新型AgC触头,并对其机械物理性能和耐电弧磨损性能进行了系统研究。 为整体改善传统机械混粉AgC触头的机械物理性能和耐电弧磨损性能,首先从粉体制备上入手,引入化学包覆工艺改善其成分偏聚和组织不均匀性,采用高能球磨获得纳米级石墨,作为后续银原子非均质形核核心,结合还原剂液相喷雾技术制备出纳米晶AgC包覆粉,利用该粉体良好的烧结致密性能实现了块体触头性能的全面改善。 以纯度为C%>99.5%、粒度为200目的石墨粉为原料,通过QM-1SP型行星式球磨机,经过最佳球磨时间10h高能球磨后,制备出一维纳米级石墨,平均厚度50-60nm。对球磨包覆Ag-5%C粉的X衍射测试表明,制备的包覆粉中Ag的平均晶粒尺寸约为50nm。 论文研究了制备出的纳米晶AgC包覆粉体的烧结性能及其块体触头材料的机械物理性能,研究了球磨时间对触头性能及组织的影响以及烧结温度对其性能的影响,对AgC体系三种不同的粉体制备工艺触头材料进行了组织和机械物理性能对比分析并建立了简要的机理模型分析,研究了纳米晶包覆粉的配比添加对常规机械混粉触头性能的影响。 研究结果表明,随着球磨时间的增加,AgC块体触头出现了石墨定向组织。电导率均匀组织时最高,出现石墨定向组织时降低,又随定向组织的增多而回升,但材料的硬度和致密性下降。随着烧结温度的升高,触头的致密度增加,硬度上升,电导率明显提高。在840℃左右,材料性能最佳。与机械混粉和滴加-包覆工艺相比,球磨石墨喷雾-包覆工艺制备的Ag-5%C材料具有极好的机械物理性能和更加均匀的组织。新工艺中采用还原剂液相喷雾技术,大大增加了还原剂与反应溶液单位时间接触面积,提高了分散在反应溶液中的C粉充当Ag原子非均质形核核心的几率;同时大大降低了还原剂在反应溶液中的局域浓度,有效抑制了Ag原子长大速率。两方面作用下该技术实现了细化包覆粉体及其晶粒度的作用并改善了其包覆效果,更好地消除了C在Ag基体中的成分偏聚。利用球磨-包覆工艺制备的纳米晶Ag-5%C包覆粉,混合在传统的Ag-5%C机械混粉中,实现了通过利用纳米晶粉的晶粒长大填补机械混粉材料中的微小孔隙,从而达到了改善机械物理性能的目的。更多还原

【Abstract】 In view of the distinguished feature and application prospect of nanomaterials, the nanotechnology was first applied in the fabrication of silver/graphite electrical contact materials, and newly developed AgC electrical contacts were prepared in the thesis. And also, their physical and mechanical properties and arc erosion resistance were systematically researched.To improve the properties of traditional blending AgC electrical contact material, electroless plating technique was employed in powder preparation to improve their component segregation and microstructure nonuniformity. Nanocrystalline AgC coating powders were then prepared under the combination of the reducer liquid spraying-electroless plating method and nanosized graphite, which came from the high-energy milling and worked as the heterogeneous cores of Ag atoms nucleating. Because of its well sintering densification, the properties of block contacts were totally improved.The graphite powders with over 99.5% content of C and 200 mesh granularity were used as raw material and milled for the best ten hours on the QM-1SP planetary mill and one-dimension nanosized graphite was then fabricated, with the average thickness of 50-60nm. The X-ray diffraction test showed that the average grain size of Ag in the as-prepared electroless plating Ag-5%C powders was about 50nm.In the thesis, the sintering properties of fabricated nanocrystalline AgC electroless plating powders and the physical and mechanical properties of their block contacts were researched, along with the influence of milling time on their properties and microstructure and the sintering time on the properties. At the same time, the AgC contacts fabricated by three different techniques were compared on their microstructure and properties and accordingly a brief mechanism model was established. At last, the influence of nanocrystalline electroless plating powders on the properties of conventional blending AgC contacts was researched.The research showed that with milling time going, graphite orientation structure appeared in the AgC block contacts. At that time, the electrical conductivity went lower, which was highest when uniformly microstructured, but it rose again as the orientation structure growing, with the decline of its hardness and density ratio at thesame time. While with the sintering temperature growing, the density ratio, hardness and electrical conductivity of the contacts increased and arrived their highlight at about 840 °C. The Ag-5%C material fabricated by milled graphite spraying-electroless plating technique had superior physical and mechanical properties and uniform microstructure to those made by blending and dropping-electroless plating techniques. With the reducer liquid spraying-electroless plating method, the contact area between reaction solution and reducer in unit time and the ratio of graphite powders separated in the reaction solution working as heterogeneous cores of Ag atoms nucleating were greatly increased. At the same time, the local concentration of reducer in reaction solution was largely reduced, and then the growth of Ag atoms was suppressed. Because of the factors mentioned above, the refinement of electroless plating powders and their grains and the improvement of electroless plating effect were achieved, and the component segregation of graphite in the Ag matrix was well eliminated. Mixed with various content of the as-prepared nanocrystalline electroless plating powders, the micropores in blending AgC material were filled by the growth of nanocrystalline grains. As a result, the mechanical and physical properties of the fabricated contacts were improved.The uninterrupted experiment for erosion behavior of the prepared new type AgC contact and its traditional blending counterpart by breaking arcs were done by using an ASTM Contact Material Automatic Measuring Device. In the meantime, the experiment for erosion behavior of 6 group contacts, the two contacts mentioned and four blending contacts mixed with nanocrystalline electroless plating powders, by breaking arcs were done. The arc erosion resistance properties and characteristics of the as-prepared new type AgC contact material were tested and studied, and also the improvement mechanism of the former was analyzed and discussed.As was shown in the uninterrupted experiment for erosion behavior, compared with coarse graphite blending material, the new type AgC electrical contact had less average weight loss of breaking arcs and 40% higher arc erosion resistance and better resistance against welding. In the experiment for erosion behavior by stages, the samples had similar weight loss at the beginning, but with breaking time growing, the fabricated new type AgC contact showed better arc erosion resistance at every stage than blending contacts. For blending materials, the relationship between their loss and breaking times took the shape of an exponent function curve, whose exponent was larger than 1. That meant in the anaphase of breaking, the arc erosion got aggravatedand the properties of contacts got worse and even noneffective because of the existence of electric vortex erosion, which was caused by the aggravation of the potholes of contact surface. And for milling-electroless plating Ag-5%C contact, the relationship between its loss and breaking times presented the shape like a linearity function curve, which meant the weight loss tended to be stable at every stage and the situation mentioned above won’t happen. After arc erosion, such morphology characteristics were formed on the contact surface of AgC materials as loose structure, Ag enrichment structure, graphite sediment structure, arc impact crater structure, gas pore and hole structure and crack structure. Under the impact of arcs, the new type electrical contact were superior to its traditional blending counterpart to prevent the melted Ag beads to spray and get away from the matrix and keep up the formation and development of surface cracks.The new type AgC contact material, employed on the miniature circuit breakers from Schneider Shanghai low voltage terminal Apparatus Co., Ltd. and ABB Beijing low voltage Apparatus Co., Ltd., had respectively passed the short circuit circulation test by China National Centre for Quality Supervision and Test of Low Voltage Apparatus. It had been supplied to several manufacturing corporations like SSLVTA and ABB Beijing by small batch and good economic income had been achieved.Prepared by the combination of high-energy milling, electroless plating and powder metallurgy technique, with carbon nanotubes as the fiber reinforcer, the new type carbon nanotubes-reinforced AgC electrical contact material was fabricated and its National Invention Patent was applied. The carbon nanotubes aggregate employed had the size of tens of microns, which was comprised of carbon nanotubes sized 30-60nm. And the average grain size of Ag in the as-prepared carbon nanotubes-reinforced Ag-5%C electroless plating powders was about 50nm. In electroless plating powders, graphite and carbon nanotubes were coated by microsized Ag granules with flocculent structure and the floccules had small and uniform internal micropores, which was helpful to the further densification in sintering. Thus, the prepared carbon nanotubes-reinforced Ag-5%C contact showed better physical and mechanical properties compared with blending contacts and better hardness even with other milling-electroless plating contact.Although they had similar weight loss at the original stages, the new Ag-5%C electrical contact prepared by milling-electroless plating technique and nanotubes-reinforced milling-electroless plating technique showed better arc erosion更多还原