纤维种类对炭_+炭复合材料微观结构和力学性能的影响.pdf
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1、文章编号: 1007- 8827( 2014) 06- 0444- 10纤维种类对炭/炭复合材料微观结构和力学性能的影响郝名扬, 罗瑞盈, 向巧, 侯振华, 杨威, 商海东( 北京航空航天大学 物理科学与核能工程学院,北京 100191)摘要: 采用 6K 的预氧丝和炭纤维制备预制体, 通过化学气相渗积制备炭/炭复合材料。通过偏光显微镜、 拉曼光谱、 纳米硬度和三点弯曲等手段研究其微观结构和力学性能。结果表明, 预氧丝复合材料的基体为暗层和粗糙层炭, 厚度分别为 1 4-2 6m和 10 2- 11 6m; 而炭纤维复合材料的基体为光滑层和粗糙层炭, 厚度分别为 8m 和 4 4m; 预氧丝纤
2、维的模量和硬度明显小于炭纤维, 同时基体的模量和硬度随消光角的增加而降低; 低模量的基体和纤维导致预氧丝复合材料的拉伸强度、拉伸模量、 弯曲强度和模量分别降低了 145%- 242%、 9 7%- 19 8%、 7 3%- 15 4%和 15 1%- 18 6%; 但其韧性指数却提高了224%- 235%, 这是高含量的粗糙层炭和纤维的石墨化收缩所致; 同时提出了一个三单元复合模型用来模拟复合材料的拉伸模量, 模拟误差小于 9 9%。关键词: 炭/炭复合材料; 微观结构; 力学性能; 化学气相渗积中图分类号:TQ342+ 76文献标识码:A收稿日期: 2014- 05- 23; 修回日期: 2
3、014- 12- 08基金项目: 国家自然科学基金( 21071011) 通讯作者: 罗瑞盈, 教授 E- mail:ryluo buaa edu cn作者简介: 郝名扬, 博士研究生 E- mail:haomingyangniat163 comEffects of fiber- type on the microstructure andmechanical properties of carbon/carbon compositesHAO Ming- yang, LUO ui- ying, XIANG Qiao,HOU Zhen- hua, YANG Wei, SHANG Hai- don
4、g( School of physics and Nuclear Energy Engineering,Beijing University of Aeronautics and Astronautics,Beijing100191,China)Abstract:Two carbonized oxidized polyacrylonitrile fiber ( OPF)felts and one polyacrylonitrile- based carbon fiber ( CF)feltwere used as preforms to prepare two kinds of carbon/
5、carbon composites by chemical vapor infiltration, and the effect of fiber typeon the microstructure and mechanical properties of the composites were investigated The microstructure was characterized bypolar-ized light microscopy and aman spectroscopy and the mechanical properties were characterized
6、by nanoindentation and three- pointbend tests The two carbonized OPFs are surrounded by a darklaminar layer about 1 4- 2 6 m thick followed by a rough laminarlayer of about 10 2- 116 m, while the CFs are surrounded by a smooth laminar layer about 8 8 m thick and arough laminar layerof about 4 4 m Na
7、noindentation indicates that the modulus and hardness of the carbonized OPFsare obviously lower than those ofthe CFs,and the modulus and hardness of the matrix decrease with increasing extinction angle The low modulus of the matrix andthe OPFsresult in a decrease of the tensile and flexural strength
8、 by about 14 5%- 24 2% and 7 3%- 15 4% and a decrease of thetensile and flexural modulus by about 9 7%- 19 8% and 15 1%- 18 6%,respectively,for the OPF- derived composites comparedwith the CF- derived composites However,for the OPF- derived composites the ductility factor increases by about 224%- 23
9、5% be-cause of the high content of rough laminarcarbon and the obvious shrinkage of the OPFs after graphitization Meanwhile,a modelin-volving the three components in the composites is proposed to predict their tensile modulus,which shows deviations between experi-mental and predicted results below 9
10、9%Keywords: Carbon/Carbon composites;Microstructure;Mechanical properties;Chemical vapor infiltrationFoundation item:National Natural Science Foundation of China ( 21071011)Corresponding author:LUO ui- ying,Professor E- mail:ryluo buaa edu cnAuthor introduction:HAO Ming- yang,Ph D E- mail:haomingyan
11、gniat163 comEnglish edition available online ScienceDirect (http: www sciencedirect comsciencejournal18725805 ) DOI: 10 1016/S1872- 5805( 14) 60149- 9第 29 卷第 6 期2014 年 12 月新型炭材料NEW CABON MATEIALSVol 29No 6Dec 20141IntroductionCarbon/carbon ( C /C ) composites are widelyused for structural and fricti
12、onal applications in aero-nautic and space industries,as well as brake materialfor high speed vehicles owing to their high specificstrength,stiffness and toughness,self- lubricating ca-pability,low thermal expansion coefficient and out-standing refractory properties1- 3 Chemical vapor in-filtration
13、( CVI)of carbon fiber ( CF)preforms is theaccepted process for mass production of the C /C com-posites used in the aircraft brake industry4 But thehigh cost largely limits their civil applications such asbuilding materials,sport accessories and biologicalprostheses because of the expensive high modu
14、lus CFsand the long densification time5 A simple and ef-fective way to cut the cost is to substitute the highmodulus CFs by the cheap oxidized polyacrylonitrilefibers ( OPFs)obtained by oxidation of polyacryloni-trile fibers in a temperature range of 200- 300 inair6 Moreover,Jia et al7 reported that
15、 the elonga-tion to break of the OPFs is almost four times as highas that of the CFs,which is advantageous for wea-ving Manocha et al8 and Ko et al9 have used OPFco- carbonization with resins to make the C /C com-posites with acceptable mechanical properties Chenet al10 have studied the mechanical p
16、roperties of theC /C composites from the carbonized OPF preformswith CVI/resin carbon hybrid matrix and found thatthe flexural strength ( 100- 115 MPa)was low More-over,Su et al11 have used the CF cloth and the OPFfelt alternately needled as preforms to prepare the C /Ccomposites with remarkable abl
17、ative behaviors How-ever,the fiber- types,which are important to deter-mine the microstructure and mechanical properties ofcomposites,have hardly been taken into account informer studies, and the essential information related totheir effects on the microstructure and mechanicalproperties is relative
18、ly rareThe current work is to compare the microstructureand mechanical properties of the C/C composites pre-pared from carbonized OPF felts with those from CFfelts Because the carbonization of the OPFs has beenhighlighted by previous researchers 12 ,this process isnot discussed and taken into accoun
19、t here So,theproperties of the OPFs after carbonization are only mo-nitored and used directly to compare with that of CFs2Experimental2 1Material preparationNeedle- punched integrated felts were used as pre-forms and the mass ratio of non- woven cloth to short-cut fiber web was 7 3 The fiber types o
20、f the feltswere OPFs ( Jilin carbon plant,China) ,OPFs ( TohoTenax,Japan)and CFs ( Jilin carbon plant,China)named as Nos 1,2 and 3,respectively Moreover,the obtained C /C composites were denoted using thesame names as their preforms The CF felt was usedfor comparison purpose and the two OPF felts we
21、reused to confirm the conclusion The thickness of OPFand CF felts was about 25 and 20 mm,respectivelyThe density of OPF and CF felts was 0 60 and0 45 g /cm3,respectively It is necessary for the OPFfelts to be carbonized before densification because thetwo OPF felts exhibit high shrinkages in cross-
22、sectionand length when used for CVI directly10, 13 To char-acterize the performance of the OPFs after carboniza-tion,6 K OPFs the same as the OPFs for the feltswere selected for this work The carbonization was asfollows:room temperature 200 for 5 h;200-550 for 20 h;550- 700 for 10 h;700- 900 for10h;
23、 900- 1000 for 10 h; 1000 for 2 h Both theOPFs and their felts were carbonized in an N2( purity,99 99%)environment in carbonization furnace with-out stretching The density of the OPF felts after car-bonization was about 0 45 g /cm3 The felts were di-rectly used as preforms after carbonization withou
24、thigh- temperature treatmentThe CF preforms wereheat- treated at 2300 for 2 h After all of the pre-forms were machined to the size of 200 20 mm,they were densified by isothermal CVI,using naturalgas as pyrocarbon precursor,hydrogen as dilute andcarrier gas at a temperature of 1050- 1080 under apress
25、ure of 1- 5 kPa The volume ratio of natural gas/hydrogen was 2/1 The three kinds of preforms wereinfiltrated about for 400 h and the crust was removedby machining every 50 h in the last 200 h The finalbulk density of the three preforms was 1 722,1 718and 1 715 g /cm3for Nos 1,2 and 3,respectively,an
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