高强石墨基复合材料的低成本制备与性能研究
发布时间：2018-11-03 12:21
【摘要】：本论文针对核反应堆主泵推力轴承和其他止推轴承用轴瓦对高强度、低摩擦系数石墨的需求,以天然鳞片石墨为原料,采用碳化硅弥散强化和碳化硅/碳纤维复合强化技术结合一步热压工艺制备了高强石墨基材料；系统研究原料比例和制备工艺对石墨复合材料密度、强度、摩擦性能、传导性能的影响规律。研究工作主要包括以下方面： (1)向天然鳞片石墨中引入硅粉,通过原位反应合成碳化硅增强相,得到碳化硅增强的石墨基复合材料。随着硅粉含量从0提高到37.49wt%,复合材料的抗弯强度从59MPa单调上升到206MPa。引入硅粉原位反应生成的碳化硅使复合材料致密化,提高了复合材料的传导性能,随着硅粉含量的增加,复合材料的传导性能下降,但强度和传导性能的提高并没有导致复合材料润滑性能的下降,硅粉含量小于31.46wt%时,复合材料的摩擦系数保持在0.1左右,润滑性能与商品石墨相当。 (2)分散在石墨中的硅粉在高温作用下发生液化并向石墨颗粒间流动渗透,浸润石墨；石墨碳向液相硅中扩散溶解,并与硅反应生成碳化硅；生成的碳化硅具有准片状形貌,与石墨界面结合良好,极大提高了材料的整体强度；但液硅的流动聚集也导致了碳化硅的团聚,降低了弥散均匀性。 (3)为改善碳化硅在石墨中的弥散均匀性,直接向石墨基体中加入碳化硅粉体,在热压和烧结助剂的作用下,碳化硅和基体石墨之间形成了包埋和嵌入界面结构,使石墨强度显著提高：随着碳化硅含量从0增加到40vo1%,复合材料的抗弯强度从59MPa提高到180MPa,摩擦系数保持在0.1左右,与商品高强石墨相当；继续提高碳化硅含量到50vo1%,虽然复合材料的抗弯强度提高到236MPa,但摩擦系数急剧增长到0.23。 (4)与原位反应生成方式相比,直接加入碳化硅颗粒时由于碳化硅与石墨之间没有相互扩散,界面结合弱；但这种弱界面连接避免了摩擦过程中的粘着剥落,降低了摩擦损耗。 (5)将短切碳纤维引入鳞片石墨中,采用碳化硅-碳纤维复合强化,进一步提高石墨材料的抗弯强度。碳纤维和碳化硅均匀分散在石墨基体中,形成了碳化硅/石墨和碳纤维/碳化硅/石墨两种界面；当碳化硅和石墨体积比为3：7、碳纤维含量为5vol%时,所制备材料的抗弯强度达到221MPa,是商品高强石墨的3.7倍；摩擦系数为0.116,与高强石墨相当；磨损量为是高强纯石墨的2.3倍。 (6)强化相的引入显著改变了鳞片石墨的取向和晶格参数：高硬度碳化硅颗粒在石墨鳞片间的弥散分布阻碍了石墨在垂直于压制方向的排列取向,降低了复合材料的各向异性度;石墨(002)晶面层间距增大,微晶尺寸变小,降低了复合材料的传导性能。
[Abstract]:In this paper, natural flake graphite is used as raw material to meet the demand of high strength and low friction coefficient graphite for thrust bearing and other thrust bearing of nuclear reactor main pump. High strength graphite-based materials were prepared by silicon carbide dispersion strengthening and silicon carbide / carbon fiber composite strengthening combined with one-step hot pressing process. The effects of raw material ratio and preparation process on density, strength, friction property and conductivity of graphite composites were studied systematically. The main work includes the following aspects: (1) Silicon powder was introduced into natural flake graphite and silicon carbide reinforced phase was synthesized by in-situ reaction to obtain silicon carbide reinforced graphite matrix composite. With the increase of silicon powder content from 0 to 37.49 wt, the flexural strength of the composite increases monotonously from 59MPa to 206 MPA. The silicon carbide produced by in-situ reaction of silicon powder densifies the composites and improves the conductivity of the composites. With the increase of silicon powder content, the conductive properties of the composites decrease. However, the increase of strength and conductivity did not lead to the decrease of the lubricating properties of the composites. When the content of silica fume was less than 31.46 wt%, the friction coefficient of the composites was kept around 0.1, and the lubricating property was equivalent to that of the commercial graphite. (2) the silica powder dispersed in graphite is liquefied and infiltrated into graphite particles at high temperature, and graphite carbon diffuses and dissolves in liquid silicon and reacts with silicon to form silicon carbide; The formed silicon carbide has quasi-flake morphology and good bonding with graphite interface, which greatly improves the overall strength of the material, but the flow and aggregation of liquid silicon also lead to the agglomeration of silicon carbide and decrease the dispersion uniformity. (3) in order to improve the dispersion uniformity of sic in graphite, silicon carbide powder was added directly to graphite matrix. Under the action of hot pressing and sintering assistant, the interfacial structure between sic and graphite was formed. With the increase of sic content from 0 to 40V1, the flexural strength of the composites increases from 59MPa to 180MPa, and the friction coefficient remains about 0. 1, which is equivalent to that of commercial high strength graphite. While the flexural strength of the composites increased to 236 MPA, the friction coefficient increased sharply to 0.23 MPA. (4) compared with in-situ reaction, the interface bonding is weak when silicon carbide particles are added directly because there is no diffusion between silicon carbide and graphite; But this kind of weak interface connection avoids the adhesion and spalling in the friction process and reduces the friction loss. (5) the short cut carbon fiber was introduced into the flake graphite, and the flexural strength of the graphite material was further improved by the composite strengthening of silicon carbide and carbon fiber. Carbon fiber and silicon carbide are uniformly dispersed in graphite matrix, forming silicon carbide / graphite and carbon fiber / silicon carbide / graphite interface. When the volume ratio of silicon carbide to graphite is 3: 7 and the content of carbon fiber is 5 vol%, the bending strength of the prepared material is 221 MPA, which is 3.7 times of that of commercial high strength graphite, and the friction coefficient is 0.116, which is equivalent to that of high strength graphite. The wear rate is 2.3 times higher than that of high strength pure graphite. (6) the introduction of strengthening phase significantly changed the orientation and lattice parameters of flake graphite. The dispersion distribution of high hardness silicon carbide particles between graphite flakes hindered the orientation of graphite perpendicular to the pressing direction. The anisotropy of composites is reduced. The interlayer spacing of graphite (002) crystal layer increases and the microcrystalline size becomes smaller, which reduces the conductivity of the composites.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB332
本文编号：2307774
[Abstract]:In this paper, natural flake graphite is used as raw material to meet the demand of high strength and low friction coefficient graphite for thrust bearing and other thrust bearing of nuclear reactor main pump. High strength graphite-based materials were prepared by silicon carbide dispersion strengthening and silicon carbide / carbon fiber composite strengthening combined with one-step hot pressing process. The effects of raw material ratio and preparation process on density, strength, friction property and conductivity of graphite composites were studied systematically. The main work includes the following aspects: (1) Silicon powder was introduced into natural flake graphite and silicon carbide reinforced phase was synthesized by in-situ reaction to obtain silicon carbide reinforced graphite matrix composite. With the increase of silicon powder content from 0 to 37.49 wt, the flexural strength of the composite increases monotonously from 59MPa to 206 MPA. The silicon carbide produced by in-situ reaction of silicon powder densifies the composites and improves the conductivity of the composites. With the increase of silicon powder content, the conductive properties of the composites decrease. However, the increase of strength and conductivity did not lead to the decrease of the lubricating properties of the composites. When the content of silica fume was less than 31.46 wt%, the friction coefficient of the composites was kept around 0.1, and the lubricating property was equivalent to that of the commercial graphite. (2) the silica powder dispersed in graphite is liquefied and infiltrated into graphite particles at high temperature, and graphite carbon diffuses and dissolves in liquid silicon and reacts with silicon to form silicon carbide; The formed silicon carbide has quasi-flake morphology and good bonding with graphite interface, which greatly improves the overall strength of the material, but the flow and aggregation of liquid silicon also lead to the agglomeration of silicon carbide and decrease the dispersion uniformity. (3) in order to improve the dispersion uniformity of sic in graphite, silicon carbide powder was added directly to graphite matrix. Under the action of hot pressing and sintering assistant, the interfacial structure between sic and graphite was formed. With the increase of sic content from 0 to 40V1, the flexural strength of the composites increases from 59MPa to 180MPa, and the friction coefficient remains about 0. 1, which is equivalent to that of commercial high strength graphite. While the flexural strength of the composites increased to 236 MPA, the friction coefficient increased sharply to 0.23 MPA. (4) compared with in-situ reaction, the interface bonding is weak when silicon carbide particles are added directly because there is no diffusion between silicon carbide and graphite; But this kind of weak interface connection avoids the adhesion and spalling in the friction process and reduces the friction loss. (5) the short cut carbon fiber was introduced into the flake graphite, and the flexural strength of the graphite material was further improved by the composite strengthening of silicon carbide and carbon fiber. Carbon fiber and silicon carbide are uniformly dispersed in graphite matrix, forming silicon carbide / graphite and carbon fiber / silicon carbide / graphite interface. When the volume ratio of silicon carbide to graphite is 3: 7 and the content of carbon fiber is 5 vol%, the bending strength of the prepared material is 221 MPA, which is 3.7 times of that of commercial high strength graphite, and the friction coefficient is 0.116, which is equivalent to that of high strength graphite. The wear rate is 2.3 times higher than that of high strength pure graphite. (6) the introduction of strengthening phase significantly changed the orientation and lattice parameters of flake graphite. The dispersion distribution of high hardness silicon carbide particles between graphite flakes hindered the orientation of graphite perpendicular to the pressing direction. The anisotropy of composites is reduced. The interlayer spacing of graphite (002) crystal layer increases and the microcrystalline size becomes smaller, which reduces the conductivity of the composites.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB332
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