液相气化法制备碳/碳复合材料工艺研究

探索了一种快速制备碳 /碳复合材料的新工艺——液相气化 CVI法。该工艺在沉积温度 80 0～ 14 0 0℃内 ,沉积时间 3h,多孔材料表观密度可达到 1.6 8g/ cm3,致密化速率达到 1.4～ 1.7mm/ h,致密化效率比报道的常规等温 CVI工艺要快 2个数量级以上。本文根据多孔介质传质传热学理论初步分析了该工艺快速致密的根本原因 ,采用偏光显微镜及扫描电镜观察了材料的微观组织结构及热解碳的生长特征 ,并测定了材料的表观密度及力学性能     

快速凝固结合粉末冶金法制备SiCp/AZ91复合材料的组织及性能

用快速凝固结合粉末冶金法制备了SiC颗粒增强镁合金基复合材料(SiCp/AZ91)棒材,研究了SiC颗粒含量对复合材料室温力学性能及显微组织的影响.结果表明:制备的复合材料棒材中SiC颗粒在基体中分布均匀,但仍存在局部颗粒团聚现象;随SiC颗粒含量的增加,复合材料的屈服强度、抗拉强度和断后伸长率均逐渐降低;热挤压过程中,镁、SiC和SiO2之间发生了界面反应,在界面生成Mg2Si等脆性相,影响了复合材料的界面性能.     

三维编织碳/碳复合材料(C/C)的拉伸性能及损伤

C/C复合材料具有优异的高温性能 ,采用编织结构可改善其受外载时的内部应力状态 ,提高力学性能。但是 ,三维编织 C/C复合材料结构、组织的多样性 ,加大了其性能及损伤研究的难度。本文主要研究了三维编织 C/C复合材料的拉伸性能及损伤扩展过程 ,分析了影响性能的主要因素 ,并总结了材料的损伤破坏方式     

催化FBCVI制备碳纳米纤维增强碳/碳复合材料的组织与力学性能研究

采用薄膜沸腾气相沉积(film-boiling chemical vapor infiltration,FBCVI)工艺,制备原位碳纳米纤维增强碳/碳复合材料(carbon nanofibers-reinforced carbon/carbon composites,CNFs-C/C))。研究了致密化过程中CNFs的生长情况和催化剂的引入对材料组织结构和力学性能的影响。研究表明,致密化前期,原位生长CNFs困难;随着沉积时间延长,CNFs大量增多并被碳基体包覆,CNFs主要为碳纳米线(carbon nanowires,CNWs)。CNFs-C/C的碳基体结构为粗糙层(RL),且存在大量的生长锥。相比于未加催化剂的试样,CNFs-C/C的弯曲强度和模量分别提高了30.9%和39.1%,断裂模式为假塑性断裂。     

气相沉积制备C/C复合材料微观组织分析

详细分析了等温 CVI法制备的 C/ C复合材料中基体碳的组织形貌 ,主要对光滑层、粗糙层及各向同性组织的特征作了详细描述 ,并且分析了各种工艺条件对组织形成的影响 ,首次指出沉积空间的大小影响热解碳的成核和生长并最终导致形成不同的组织。用偏光显微照片中的热解碳组织与断口 SEM形貌作对比 ,证明在层状热解碳的层间存在内应力。     

B4C/Al复合材料的组织、力学性能和制备研究进展

B4C颗粒增强铝基复合材料不仅比强度高、耐磨性能优异,还兼具多种功能特性,是核工业、航空航天、汽车工业等领域中不可缺少的结构材料和功能材料.综述了B4C/Al复合材料的研究现状,总结了搅拌铸造法、粉末冶金法和冷喷涂增材制造法等各种方法的优缺点,对比了不同工艺下制备的B4C颗粒增强铝基复合材料的硬度、拉伸强度、屈服强度、...     

自加热化学液相沉积法制备炭/炭-SiC复合材料及其抗氧化性能

以液态炭源为前驱体、炭毡为增强体,采用自加热化学液相法,以二次沉积法制备了炭/炭-SiC复合材料;考察了温度和氧化时间对该材料质量损失的影响.结果表明:炭/炭-SiC复合材料的抗氧化性能较炭/炭复合材料大幅度提高,质量损失率仅为炭/炭复合材料的15%～20%.     

毡基和碳布叠层C/C复合材料的高温力学及抗氧化性能比较

借助三点弯曲、氧化试验和扫描电镜观察,对毡基C/C复合材料的抗氧化性能和高温1973K下的力学性能进行了研究,并和2DC/C复合材料的相应性能作了对比。结果表明:虽然毡基C/C复合材料和2DC/C复合材料的高温力学性能均优于室温力学性能,但毡基C/C复合材料主要以纤维断裂的形式发生弯曲破坏,而2DC/C复合材料主要以基体的层间开裂发生弯曲破坏,所以毡基C/C的弯曲强度、模量较高;另外,毡基C/C复合材料的整体结构可有效抵御热应力开裂,表现为高温条件下具有较强的抗氧化性能。     

C/Al-40%Cu复合材料的原位热解-热压法制备及微观结构

以聚乙烯醇缩丁醛为碳源,采用原位热解-热压法制备C/Al-40%Cu(体积分数)复合材料,研究了该复合材料的物相组成、微观结构以及界面反应特性。结果表明:复合材料主要由铝相、铜相、原位生成的碳材料以及少量残留的高分子材料组成,碳材料连续存在于铝、铜相颗粒之间,有效抑制了Al2Cu和Al4Cu9等金属间化合物的生成;复合材料的实测密度接近于理论密度,组织中未见明显孔洞,致密程度较高;复合材料界面结合良好,铝相和铜相、铝相和碳材料层之间均发生了元素互扩散,形成了厚度分别为2.0~3.5μm和1.0~1.5μm的扩散层,铜相和碳材料层之间以机械结合方式连接。     

密度梯度碳/碳复合材料的制备及性能

采用强制流动热梯度化学气相渗透法在1000～1 250℃制备了密度梯度碳/碳复合材料;借助三点弯曲试验和激光闪烁法测定了复合材料的弯曲性能与导热系数,用偏光显微镜及扫描电子显微镜观察了基体热解碳的组织结构及断口形貌。结果表明:该复合材料上层的最大密度为1.65g·cm~(-3),下层的最小密度为1.10g·cm~(-3),具有明显的密度梯度;复合材料的密度越大,抗弯强度越高;其导热系数也随密度的增加而增大;沉积温度是影响基体热解碳组织的主要因素,高温有利于粗糙层热解碳的生成,而低温有利于光滑层热解碳的生成。     

Characterization of surface grooves and scratches induced by friction of C/C composites at low and high temperatures

Friction experiments were conducted on C/C composites at low and high temperatures during braking with the use of a pin-on-disc tribometer. The surface grooves formed were investigated by an optical camera and a laser profilometer, while scratches were characterized by optical microscopy. Damages were correlated with tribological performances (friction and wear). It is shown that friction at low temperature leads to high friction coefficient and wear rate, and to surfaces strongly grooved and abraded. For friction experiments performed at high temperature, they lead to lower friction coefficient and wear, and the resulting surfaces are rather smooth and slightly grooved.     

Structural and chemical study of C/C composites before and after braking tests

The oxygen, nitrogen, and hydrogen contents of three kinds of C/C composites used for brake discs, before and after braking tests, have been measured by a combustion-infrared method. The morphologies of wear debris have been observed by SEM, and the relationships between their oxygen, nitrogen, and hydrogen contents and crystal structures and friction properties have been established. The results have shown that the oxygen, nitrogen, and hydrogen contents of the C/C composites are mainly determined by structural defects, and are independent of the degree of anisotropy; the greater the number of lattice defects, the higher the contents of oxygen, nitrogen, and hydrogen. Oxygen, nitrogen, and hydrogen were desorbed during the braking tests, but they were re-adsorbed on the friction surface and wear debris in greater amounts after braking. The oxygen content directly affects the friction behavior; the greater the amount of oxygen desorbed, the greater the increase in friction coefficient, that is, the worse the stability of friction.     

沥青基碳/碳复合材料常压浸渍-碳化工艺及组织

对常压下液相浸渍 -碳化法制备沥青基 /碳复合材料工艺及致密规律进行了研究 ,并对所得制件的基体组织结构进行分析 ,从理论上解释其产生的原因 ,为制定工艺规范提供根据和指导     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

B4C/6061Al复合材料焊接接头组织与力学性能研究*

基于碳化硼中¹⁰B同位素优良的热中子吸收能力,铝基碳化硼复合材作为中子吸收材料越来越多的应用于核电站中。但碳化硼颗粒的加入使该材料的可焊性变差,因此研究其焊接行为变得十分必要。采用钨极氩弧焊(Tungsten inert gas,TIG)和搅拌摩擦焊(Friction stir welding,FSW)对体积分数为30%的B₄C/6061Al复合材料进行焊接,研究不同焊接方法、焊缝填充材料对复合材料对接接头微观组织及力学性能的影响。B₄C/6061Al复合材料焊接接头拉伸性能如下：FSW焊>TIG焊(Al-Si焊丝)>TIG焊(6061Al焊丝)>TIG焊(6061Al-Mg焊丝)>TIG焊(无填充)。TIG焊缝区容易产生气孔、B₄C颗粒分布不均匀及有害生成相是导致其力学性能不佳的主要原因。FSW可以有效避免基体金属与增强相的高温化学反应,使得焊缝区的晶粒细化,增强相颗粒的分布比TIG焊均匀,为30%B₄C/6061Al复合材料最佳焊接方法,其接头的室温拉伸强度达247 MPa,为母材强度的85%。     

Structure and water-lubricated tribological properties of Cr/a-C coatings with different Cr contents

The Cr containing amorphous carbon coatings (Cr/a-C) with varying Cr content were deposited using unbalanced magnetron sputtering. The results revealed that the chromium carbide nano-clusters were formed when the Cr content exceeded 4.9 at%. The critical load increased while the hardness decreased after the Cr element incorporation. Although the low Cr containing Cr/a-C coatings (≤4.9 at%) exhibited similar friction coefficient with a-C coatings, but the initial friction coefficient, running-in distance and wear rate of SUS440C balls all decreased. However, the Cr/a-C coatings with high Cr content (11.98–14.09 at%) would worsen the tribological properties because chromium carbides acted as abrasive wear particles during tribotests.     

空气/氮气气氛下电流和摩擦速度对C/C复合材料载流摩擦磨损性能的影响

在空气/氮气气氛下研究了电流、摩擦速度、载荷等试验参数对C/C复合材料载流磨损率和摩擦因数的影响,并对磨损表面的形貌和成分进行了观察和分析。结果表明:随着电流和摩擦速度增大,C/C复合材料的磨损率和摩擦因数均增大;相较于空气气氛,氮气气氛下的摩擦因数较高,磨损率较低;空气气氛中炭材料的氧化加剧了材料的磨损,使得磨损率较高,而摩擦过程中材料表面形成的氧化膜使得摩擦因数较低。     

Effect of rare earths on mechanical and tribological properties of carbon fibers reinforced PTFE composite

The effect of a rare earth (RE) surface treatment on the mechanical and tribological properties of carbon fiber (CF) reinforced polytetrafluoroethylene (PTFE) composites was experimentally investigated. The tensile properties of the CF reinforced PTFE (CF/PTFE) composites treated with air oxidation and RE modifier were superior to those of untreated CF/PTFE composites, while RE treatment was most effective in promoting the tensile strength and strain at break of the CF/PTFE composite. The bending strength of the RE treated CF/PTFE composite was improved by about 16% compared with that of untreated composites, while 2% improvement was achieved by air oxidation. Under oil-lubricated conditions, RE treatment was more effective than air oxidation to reduce the friction coefficient and wear of PTFE composite. RE treatment effectively improved the interfacial adhesion between CF and PTFE. The strong interfacial coupling of the composite made CF not easy to detach from the PTFE matrix, and prevented the rubbing-off of PTFE, accordingly improved the friction and wear properties of the composite.