沉积温度对CVI+PIP工艺C/C复合材料微观组织及磨损性能的影响

采用化学气相浸渗(CVI)与聚合物浸渍裂解法(PIP)相结合的工艺制备碳/碳(C/C)复合材料,利用CFT-I型材料表面性能综合试验仪对C/C复合材料进行往复摩擦磨损测试,采用扫描电镜对C/C复合材料的微观组织与摩擦磨损试验后的表面形貌进行表征,研究了沉积温度对CVI+PIP工艺C/C复合材料微观组织与摩擦磨损性能的影响规律。结果表明:与石墨材料相比,C/C复合材料具有更加理想的摩擦磨损性能;沉积温度为1050℃制得的C/C复合材料具有稳定的摩擦系数和最低的磨损率,在该温度下产生的孔洞和裂纹极少,浸渗效果最为理想。

利用束丝复合材料对PIP工艺制备2D-SiC_f/SiC复合材料力学性能进行表征

为了找到一种能有效对陶瓷基复合材料先驱体浸渍裂解(PIP)工艺参数进行优化的方法,提出利用束丝复合材料对二维复合材料力学性能进行表征的方案。对5种PIP工艺条件制备的束丝以及二维SiCf/SiC复合材料在不同PIP工艺条件下力学性能变化规律进行了研究,并对采用束丝复合材料对二维复合材料力学性能表征的有效性进行了分析。研究表明,束丝复合材料和二维复合材料力学性能随PIP工艺的变化规律完全相同,这是因为两种复合材料界面、纤维损伤等特性基本相同。采用强度比对两种复合材料力学性能一致程度进行了表征,结果表明两者一致性较好,但随PIP工艺复杂程度的提高,两者一致性降低。利用束丝复合材料可以对二维复合材料力学性能进行较好的表征,可对二维等实体复合材料制备工艺进行初步优化,从而使材料工艺设计效率大为提高。

PIP工艺对2DC／SiC-ZrB2复合材料结构和力学性能的影响

采用CVI结合SI及PIP工艺制备2D C/SiC-ZrB2复合材料。研究了PIP工艺中循环浸渍次数及热处理对复合材料结构和力学性能的影响。比较了多孔C/SiC浸渍浆料后用PIP结合CVI致密化和仅用CVI致密化的效果。结果表明:浸渍裂解后,热处理温度相同,热处理次数对复合材料的开孔率和弯曲强度影响不大。2D C/SiC-ZrB2复合材料的弯曲强度不随PIP次数的增多而增加,PIP处理二次后,复合材料的强度逐渐增加,PIP处理五次,强度达到最大值,制备的复合材料开孔率为8.0%、弯曲强度为423 MPa。SI后用PIP结合CVI致密化比仅用CVI致密化效果好。

Al粉作为活性填料对PIP法SiC_f/SiC复合材料性能的影响

利用2.5D SiC纤维预制件,通过前驱体浸渍裂解法(PIP法)制备SiC_f/SiC复合材料,通过在第一次浸渍浆料中加入活性Al粉和惰性颗粒SiC粉来提高浸渍效率.研究了活性填料的加入以及纤维表面热解碳层的厚度对材料性能的影响.结果表明,由于Al粉在热解过程中与含碳有机小分子发生化学反应生成新的物相,使得复合材料的力学性能得到了很大的提高,在1200℃经过六个周期的浸渍裂解后,复合材料的三点弯曲强度达到441MPa,比例极限应力达到380MPa.在200～500nm厚度范围内,热解碳的厚度对复合材料的抗弯强度影响不明显.复合材料的弹性模量随着热解碳层厚度的增加而降低.

PIP工艺对2D高硅氧/甲基硅树脂复合材料结构与性能的影响

研究了不同浸渍工艺对2D高硅氧织物增强甲基硅树脂复合材料结构与性能的影响。结果表明,复合材料的密度及抗氧化性随着浸渍循环次数和热裂解温度的增加而增加;当热裂解温度不高于400℃时,复合材料仍具有较好的假塑性;但当热裂解温度高于400℃时,复合材料表现为典型的脆性断裂。当浸渍过程中热裂解温度为400℃、循环次数为2次时,500℃热处理20 m in的复合材料的室温弯曲强度最高,为49.8 MPa,比未处理的提高了150%。

CVI-PIP法制备连续纤维增韧碳化硅基复合材料的研究

CMC-SiC是航空航天等高科技领域不可缺少的材料。先驱体浸渍热解(PIP)和化学气相渗透(CVI)是制备CMC-SiC较为理想的方法。采用PIP和CVI相结合的技术制备了CMC-SiC。结果表明,制备CMC-SiC的最好工艺是初始进行短期的CVI过程,随后再进行反复的PIP循环。

Novel C_(sf)/SiBCN composites prepared by densifying C_(sf)/MA-SiBCN with the PIP process:Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.

KD-S SiC_f/SiC composites with BN interface fabricated by polymer infiltration and pyrolysis process

Continuous silicon carbide fiber reinforced silicon carbide matrix(SiC_f/SiC) composites are attractive candidate materials for aerospace engine system and nuclear reactor system. In this paper, SiC_f/SiC composites were fabricated by polymer infiltration and pyrolysis(PIP) process using KD-S fiber as the reinforcement and the LPVCS as the precursor, while the BN interface layer was introduced by chemical vapor deposition(CVD) process using borazine as the single precursor. The effect of the BN interface layer on the structure and properties of the SiC_f/SiC composites was comprehensively investigated. The results showed that the BN interface layer significantly improved the mechanical properties of the KD-S SiC_f/SiC composites. The flexure strength and fracture toughness of the KD-S SiC_f/SiC composites were evidently improved from 314±44.8 to 818±39.6 MPa and 8.6± 0.5 to 23.0±2.2 MPa·m^(1/2), respectively. The observation of TEM analysis displayed a turbostratic structure of the CVD-BN interface layer that facilitated the improvement of the fracture toughness of the SiC_f/SiC composites. The thermal conductivity of KD-S SiC_f/SiC composites with BN interface layer was lower than that of KD-S SiC_f/SiC composites without BN interface layer, which could be attributed to the relative low thermal conductivity of BN interface layer with low crystallinity.

3D C_f/SiBCN composites prepared by an improved polymer infiltration and pyrolysis

Using liquid poly(methylvinyl)borosilazanes(PMVBSZ)as precursor,carbon fiber reinforced SiBCN matrix composites(C_f/SiBCN)were fabricated by a modified polymer infiltration and pyrolysis(PIP)process.With dicumyl peroxide added as cross-linking agent,the PMVBSZ could be solidified at a low temperature of 120℃,leading to a high ceramic yield of～70%.The cross-linking mechanism and ceramization processes of the precursor were investigated in detail.Moreover,a modified infiltration technology was developed,which improved the efficiency and protected the precursor against moist air during PIP.Consequently,the obtained C_f/SiBCN composites had an oxygen content of around 1.22 wt%.Benefiting from the high ceramic yield and high efficiency of the modified PIP,C_f/SiBCN composites with an open porosity of～10%and uniform microstructure were obtained after only 7 cycles of PIP.The flexural strength and fracture toughness of the derived C_f/SiBCN composites were 371 MPa and 12.9 MPa·m^(1/2),respectively.This work provides a potential route for the fabrication of high performance C_f/SiBCN composites.

Progress in Recrystallized SiC and Its Composites

Recrystallized silicon carbide（ RSi C）,a high purity Si C material sintered by the process of evaporation-condensation without any additives,is one of the most important structural materials in the fields of high temperatures. However,its low density and porous structure caused by the sintering mechanism in the absence of shrinkage,restrict its wide applications in engineering.This paper reviews the research progress and related technologies on the preparation of high-density RSi C and its composites. RSi C with relative high density up to 2. 75g·cm- 3can be obtained by a combination of pretreatment to Si C raw materials such as reshaping,modification and particle size distribution,and appropriate forming method. Post treatments such as cyclic pyrolysis and impregnation- recrystallization,and slurry impregnation- recrystallization are needed for the further density increase of RSi C（ 2. 99 g·cm- 3）. In addition,high performance RSi C- Mo Si2 and RSi C- Al composites obtained by melt infiltration are also reviewed.

Microstructural regulation,oxidation resistance,and mechanical properties of C_(f)/SiC/SiHfBOC composites prepared by chemical vapor infiltration with precursor infiltration pyrolysis

To further improve the oxidation resistance of polymer derived ceramic(PDC)composites in harsh environments,Cf/SiC/SiHfBOC composites were prepared by chemical vapor infiltration(CVI)and precursor impregnation pyrolysis(PIP)methods.The weight retention change,mechanical properties,and microstructure of C/SiC/SiHfBOC before and after oxidation in air were studied in details.Microscopic analyses showed that only the interface between the ceramics and fibers was oxidized to some extent,and hafnium had been enriched on the composite surface after oxidizing at different temperature.The main oxidation products of Cf/SiC/SiHfBOC composites were Hf0_(2)and HfSi04 after oxidation at 1500℃for 60 min.Moreover,the weight retention ratio and compressive strength of the Cf/SiC/SiHfBOC composites are 83.97%and 23.88±3.11 MPa,respectively.It indicates that the Cf/SiC/SiHfBOC composites should be promising to be used for a short time in the oxidation environment at 1500℃.

A novel mullite anti-gyroid/SiC gyroid ceramic metastructure based on digital light processing 3D printing with enhanced electromagnetic wave absorption and mechanical properties

Sic-based composites are widely used as electromagnetic wave absorbers due to their excellent dielectric properties.However,the constraints associated with structural design and the intricacies of the preparation process hinder their broader application.In this study,novel mullite anti-gyroid/SiC gyroid metastructures are designed to integrate the mechanical and electromagnetic wave(EMW)absorption properties of composite materials.Mullite anti-gyroid/SiC gyroid composites are fabricated utilizing a combination of digital light processing(DLP)three-dimensional(3D)printing and precursor infiltration and pyrolysis(PiP)processes.Through the modulation of structural units,the electromagnetic parameters can be effectively regulated,thus improving the impedance matching characteristics of the composites.The structural composites show outstanding EMW absorption properties,with a minimum reflection loss of-54 dB at a thickness of 1.9 mm and an effective absorption bandwidth of 3.20 GHz at a thickness of 2.2 mm.Furthermore,the PIP process significantly enhances the mechanical properties of the composites;compared with those of the mullite/SiC ceramics,the flexural strength of the composites is improved by 3.69-5.85 times(13.28±1.15 MPa vs.(49.05±1.07)-(77.78±3.72)MPa),and the compressive strength is improved by 4.59-13.58 times(8.55±0.90 MPa vs.(39.02±1.63)-(116.13±2.58)MPa).This approach offers a novel and effective method for fabricating structural composites with an expanded range of higher electromagnetic wave absorption properties and improved mechanical properties.

高性能C/SiC复合材料的快速制备

研究开发了“CVI+PIP”组合工艺 ,本着“低成本、短研制周期 ,适合批量化生产”的目的 ,研制的C/SiC复合材料弯曲强度高达 5 6 1MPa ,断裂韧性高达 17MPa·m1/2 ,制成的C/SiC复合材料推力室开孔率小于 2 % ,在0 .6MPa气压下不漏气。

聚合物浸渍裂解法制备C/C-ZrC-SiC-ZrB2复合材料及其性能研究

以有机ZrC、ZrB2前驱体和聚碳硅烷的混合溶液为浸渍前驱体,利用聚合物浸渍裂解法(PIP)制备了C/C-ZrC-SiC-ZrB2复合材料,并对材料的微观形貌、弯曲和烧蚀性能进行了研究。研究结果表明:利用该方法可制备出陶瓷相填充充分且分布均匀的C/C-ZrC-SiC-ZrB2复合材料。材料的弯曲强度为126.31 MPa,断面有大量的纤维束拔出,表现出良好的假塑性断裂模式。经过120 s氧–乙炔烧蚀,材料无明显烧蚀,其线烧蚀率和质量烧蚀率分别为–2.50×10-4mm/s和–1.33×10-4g/s。在材料表面不同区域形成不同的保护层,不仅能够降低氧气和热流向材料内部扩散,还具有弥补缺陷的作用,使材料表现出优异的抗烧蚀性能。

活性填料在先驱体转化法纤维增强陶瓷基复合材料中的应用Ⅰ .复合材料的致密化模型

在先驱体转化陶瓷基复合材料的制备中,坯体在裂解前后的体积发生变化。引入体系体积收缩率参数,对单一先驱体转化纤维增强陶瓷基复合材料致密化模型进行了修正。同时,分别对含惰性填料和/或活性填料的先驱体浆料浸渍-裂解纤维增强陶瓷基复合材料致密化进行了模型分析。从理论上揭示了复合材料的浸渍-裂解周期与材料的理论密度和理论孔隙率之间的关系。当先驱体浆料中含有活性填料时,复合材料的理论密度和理论孔隙率与活性填料的反应陶瓷产率、反应密度比、体积收缩率有密切的数学关系。在先驱体中引入活性填料比引入惰性填料能更为有效地提高材料的密度,降低材料的孔隙率。

C/SiC复合材料的常压制备与性能研究

采用聚碳硅烷作为碳化硅先驱体,以二维0°/90°正交编织碳布叠层后作为增强体,采用真空压力浸渍的方法制备了C/SiC复合材料,研究了裂解温度和浆料浓度对复合材料性能的影响.结果表明:复合材料的弯曲强度随着裂解温度的升高以及浆料浓度的增加都呈增加趋势;基体在纤维束内部分布均匀,但依然有一些小气孔存在;在1100℃时,基体中开始生成一定量的β-SiC相,复合材料的三点弯曲强度达到232MPa,断裂韧性达到10.50MPa·m^(1/2).在断裂过程中表现出明显的韧性断裂,断口有较长的纤维拔出.

制备工艺对碳纤维增强碳化硅基复合材料结构和力学性能的影响

以化学气相沉积碳为界面层,聚碳硅烷为先驱体,经过10个周期的浸渍-裂解制备了三维编织碳纤维增强碳化硅复合材料(3D-Cf/SiC)。考察了碳涂层高温预处理和陶瓷先驱体第一个周期1600℃裂解对复合材料结构与性能的影响。结果表明:碳涂层高温预处理有助于复合材料密度的提高,弱化了复合材料的界面结合,从而显著提高了复合材料的力学性能,复合材料弯曲强度达到571 MPa,剪切强度51 MPa,断裂韧性18 MPa.m1/2。

低分子量聚碳硅烷制备3D-Cf/SiC复合材料

研究了低分子量聚碳硅烷(PCS)通过先驱体浸渍裂解(PIP)工艺制备Cf/SiC复合材料.分析表明:PCS的数均分子量为400,活性较强,陶瓷化产率为70%左右,在1200℃基本转化为微晶态的β-SiC.分别通过3种不同升温速率制备了3D-Cf/SiC复合材料试样,其弯曲强度分别为745.2 MPa、686.7 MPa和762.5 MPa,明显高于文献报道3D-Cf/SiC复合材料弯曲强度300～500 MPa的水平.试样断口的SEM照片均显示长的纤维拔出,有良好的增韧效果,低分子量PCS裂解得到的基体比较致密.实验结果说明,低分子量PCS适合于制备3D-Cf/SiC复合材料,并且提高升温裂解速率对材料性能影响很小.

新型含锆聚碳硅烷制备C/C-SiC-ZrC复合材料及烧蚀性能

目的提高C/C-SiC复合材料的抗烧蚀性能。方法通过交联固化-碳化工艺获得新型含锆聚碳硅烷(Polyzirconocenecarbosilane,PZCS)裂解产物。采用FT-IR、XPS、TG、XRD、SEM等分析手段表征PZCS先驱体基本结构和固化、裂解产物结构及元素分布等。以PZCS为溶液浸渍先驱体,通过PIP工艺制备得到C/C-SiC-ZrC复合材料,采用氧乙炔烧蚀试验表征其抗烧蚀性能。结果PZCS陶瓷先驱体经过交联固化工艺能够显著提高其陶瓷产率。TG结果表明,980℃时陶瓷产率达66.37%,所得陶瓷粉末为分散均匀的SiC-ZrC复相陶瓷。C/C-SiC-ZrC复合材料经过氧乙炔试验烧蚀600s后,其线烧蚀率为0.0067mm/s,表现出良好的抗烧蚀性能。结论SiC-ZrC复相陶瓷基体烧蚀过程中,氧化形成SiO2和ZrO2等氧化物涂层,氧化物隔离层能够隔离氧气和热量,阻止其向复合材料内部进一步扩散,可有效提高复合材料烧蚀性能。

先驱体浸渍裂解结合化学气相渗透工艺下二维半和三维织构SiC/SiC复合材料的结构与性能

通过先驱体浸渍裂解工艺结合化学气相渗透工艺(PIP+CVI)制备了二维半(2.5D)和三维(3D)编织结构的碳化硅纤维增强碳化硅基(SiC/SiC)复合材料,对两者的密度、热导率、力学性能以及微观结构等进行了测试分析。结果表明,PIP+CVI工艺制备的SiC/SiC复合材料具有较低的密度(1.98~2.43g·cm-3)和热导率(0.85~2.08 W·m^(-1)·K^(-1)),初期CVI纤维涂层能够提高纤维-基体界面剪切强度(~141.0 MPa),从而提高SiC/SiC复合材料的力学性能,后期CVI整体涂层明显提高了2.5DSiC/SiC复合材料的密度、热导率和力学性能,对3DSiC/SiC复合材料性能的影响不明显。