高強(qiáng)石墨基復(fù)合材料的低成本制備與性能研究
發(fā)布時(shí)間：2018-11-03 12:21
【摘要】：本論文針對(duì)核反應(yīng)堆主泵推力軸承和其他止推軸承用軸瓦對(duì)高強(qiáng)度、低摩擦系數(shù)石墨的需求,以天然鱗片石墨為原料,采用碳化硅彌散強(qiáng)化和碳化硅/碳纖維復(fù)合強(qiáng)化技術(shù)結(jié)合一步熱壓工藝制備了高強(qiáng)石墨基材料；系統(tǒng)研究原料比例和制備工藝對(duì)石墨復(fù)合材料密度、強(qiáng)度、摩擦性能、傳導(dǎo)性能的影響規(guī)律。研究工作主要包括以下方面： (1)向天然鱗片石墨中引入硅粉,通過原位反應(yīng)合成碳化硅增強(qiáng)相,得到碳化硅增強(qiáng)的石墨基復(fù)合材料。隨著硅粉含量從0提高到37.49wt%,復(fù)合材料的抗彎強(qiáng)度從59MPa單調(diào)上升到206MPa。引入硅粉原位反應(yīng)生成的碳化硅使復(fù)合材料致密化,提高了復(fù)合材料的傳導(dǎo)性能,隨著硅粉含量的增加,復(fù)合材料的傳導(dǎo)性能下降,但強(qiáng)度和傳導(dǎo)性能的提高并沒有導(dǎo)致復(fù)合材料潤(rùn)滑性能的下降,硅粉含量小于31.46wt%時(shí),復(fù)合材料的摩擦系數(shù)保持在0.1左右,潤(rùn)滑性能與商品石墨相當(dāng)。 (2)分散在石墨中的硅粉在高溫作用下發(fā)生液化并向石墨顆粒間流動(dòng)滲透,浸潤(rùn)石墨；石墨碳向液相硅中擴(kuò)散溶解,并與硅反應(yīng)生成碳化硅；生成的碳化硅具有準(zhǔn)片狀形貌,與石墨界面結(jié)合良好,極大提高了材料的整體強(qiáng)度；但液硅的流動(dòng)聚集也導(dǎo)致了碳化硅的團(tuán)聚,降低了彌散均勻性。 (3)為改善碳化硅在石墨中的彌散均勻性,直接向石墨基體中加入碳化硅粉體,在熱壓和燒結(jié)助劑的作用下,碳化硅和基體石墨之間形成了包埋和嵌入界面結(jié)構(gòu),使石墨強(qiáng)度顯著提高：隨著碳化硅含量從0增加到40vo1%,復(fù)合材料的抗彎強(qiáng)度從59MPa提高到180MPa,摩擦系數(shù)保持在0.1左右,與商品高強(qiáng)石墨相當(dāng)；繼續(xù)提高碳化硅含量到50vo1%,雖然復(fù)合材料的抗彎強(qiáng)度提高到236MPa,但摩擦系數(shù)急劇增長(zhǎng)到0.23。 (4)與原位反應(yīng)生成方式相比,直接加入碳化硅顆粒時(shí)由于碳化硅與石墨之間沒有相互擴(kuò)散,界面結(jié)合弱；但這種弱界面連接避免了摩擦過程中的粘著剝落,降低了摩擦損耗。 (5)將短切碳纖維引入鱗片石墨中,采用碳化硅-碳纖維復(fù)合強(qiáng)化,進(jìn)一步提高石墨材料的抗彎強(qiáng)度。碳纖維和碳化硅均勻分散在石墨基體中,形成了碳化硅/石墨和碳纖維/碳化硅/石墨兩種界面；當(dāng)碳化硅和石墨體積比為3：7、碳纖維含量為5vol%時(shí),所制備材料的抗彎強(qiáng)度達(dá)到221MPa,是商品高強(qiáng)石墨的3.7倍；摩擦系數(shù)為0.116,與高強(qiáng)石墨相當(dāng)；磨損量為是高強(qiáng)純石墨的2.3倍。 (6)強(qiáng)化相的引入顯著改變了鱗片石墨的取向和晶格參數(shù)：高硬度碳化硅顆粒在石墨鱗片間的彌散分布阻礙了石墨在垂直于壓制方向的排列取向,降低了復(fù)合材料的各向異性度;石墨(002)晶面層間距增大,微晶尺寸變小,降低了復(fù)合材料的傳導(dǎo)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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB332
本文編號(hào)：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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB332
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