材料工程  2015, Vol. 43Issue (4): 98-101   PDF    
http://dx.doi.org/10.11868/j.issn.1001-4381.2015.04.017
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文章信息

马彦, 陈朝辉. 2015.
MA Yan, CHEN Zhao-hui. 2015.
1800℃热处理对PIP法C/SiC复合材料结构和性能的影响
Effect of 1800℃ Annealing on Microstructures and Properties of C/SiC Composites Fabricated by Precursor Infiltration and Pyrolysis
材料工程, 43(4): 98-101
Journal of Materials Engineering, 43(4): 98-101.
http://dx.doi.org/10.11868/j.issn.1001-4381.2015.04.017

文章历史

收稿日期:2012-07-13
修订日期:2014-09-05
1800℃热处理对PIP法C/SiC复合材料结构和性能的影响
马彦1 , 陈朝辉2    
1. 中国人民解放军总后勤部 建筑工程研究所, 西安 710032;
2. 国防科技大学 航天与材料工程学院, 长沙 410073
摘要:采用扫描电镜(SEM)和透射电镜(TEM),研究氩气中1800℃热处理对先驱体浸渍-裂解(PIP)工艺制备三维编织C/SiC复合材料结构和性能的影响。结果表明:在1800℃热处理过程中,C/SiC复合材料的界面处发生了碳热还原反应和硅扩散,导致基体和纤维之间产生化学结合,纤维受到损伤;1800℃热处理后,PIP法C/SiC复合材料出现8%的失重率,力学性能急剧下降80%以上,断裂行为由韧性转变为脆性断裂。
关键词C/SiC复合材料    力学性能    微观结构    热处理    
Effect of 1800℃ Annealing on Microstructures and Properties of C/SiC Composites Fabricated by Precursor Infiltration and Pyrolysis
MA Yan1 , CHEN Zhao-hui2    
1. Construction Engineering Research Institute, General Logistics Department of People's Liberation Army, Xi'an 710032, China;
2. College of Aerospace and Materials Engineering, National University of Defense Technology, Changsha 410073, China
Abstract: Using SEM and TEM, the effect of 1800℃ annealing on microstructures and properties of 3D braided C/SiC composites was investigated under Ar,fabricated by PIP process. The results show that during 1800℃ annealing, the carbothermic reductions and Si diffusing happen at the interfaces of C/SiC composites, resulting in the chemical bonding between fibers and matrix, and fibers are damaged. After 1800℃ annealing, the C/SiC composites fabricated by PIP process indicate 8% mass loss rate, the mechanical properties sharply decrease over 80%, and the fracture behavior changes from toughness fracture to brittle fracture.
Key words: C/SiC composite    mechanical property    microstructure    annealing    

复合材料具有密度低、强度高和优异的高温力学性能,在航空、航天领域有广泛的应用潜力[1, 2, 3]。制备C/SiC复合材料的工艺有多种,其中先驱体浸渍裂解法(Precursor Infiltration and Pyrolysis,PIP)因为具有工艺简单、能够实现近净成型等特点[4, 5, 6, 7],成为常用工艺之一。

在应用研究中发现,当PIP法C/SiC复合材料处于1600℃高温惰性环境中时,其力学性能有所下降,但仍呈现韧性断裂,且经后续致密化工艺后力学性能能够恢复到原来水平;而当惰性环境温度继续升高,如达到1800℃时,PIP法C/SiC复合材料力学性能急剧下降,并呈现脆性断裂,且经后续致密化工艺不能再恢复[8, 9]。因此,C/SiC复合材料还不能在1800℃及以上高温环境中长时间应用。不过,张立同等[10]认为,C/SiC复合材料在1650~2200℃范围内可以工作数小时至数十小时,适用于液体火箭发动机、冲压发动机和空天飞行器热防护系统等。

本工作利用扫描电镜(SEM)和透射电镜(TEM)手段,对1800℃热处理前后PIP法C/SiC复合材料的性能和结构进行表征,研究了高温环境中该复合材料力学性能和界面结构的演变,并分析了导致此种演变发生的原因。

1 实验 1.1 材料制备

选用日本东丽公司生产的T300炭纤维,采用三维编织法制备纤维预制体,纤维的体积分数为45%。聚碳硅烷(polycarbosilane)由国防科技大学合成,其平均分子量为1742,软化点为175℃。将炭纤维预制体浸渍聚碳硅烷的二甲苯溶液,然后在1200℃惰性气氛中裂解。之后重复上述过程9~12次,得到致密度较高的C/SiC复合材料,记为试样CSC1200。最后,将试样CSC1200在氩气中进行1800℃热处理1h,记为试样CSC1800。

1.2 分析测试

根据阿基米德原理[11],采用排煤油法[11]测试材料的密度,取样数为7。抗弯强度和断裂韧性在WDW-100型电子万能试样机上测定,取样数均为5:抗弯强度采用三点弯曲法测试,试样尺寸为3mm×4mm×60mm,跨距为50mm,加载速率为0.5mm·min-1;断裂韧性采用单边切口梁法测试,试样尺寸为3.5mm×7mm×50mm,切口深度为3.5mm,跨距为30mm,加载速率为0.05mm·min-1

采用FEG S4800型扫描电境(SEM)观察试样断裂面的微观形貌,并对抛光面进行能谱分析(EDS);采用JEOL-2010型高分辨透射电子显微镜(TEM)分析试样的微观结构。

2 结果与讨论

表1是1800℃热处理前后C/SiC复合材料的力学性能。可知,试样CSC1200具有较高的力学性能,但1800℃热处理后,C/SiC复合材料出现较大的失重,同时其力学性能急剧下降。试样CSC1800的抗弯强度是CSC1200的16.4%,断裂韧性仅是CSC1200的11.3%,下降幅度均达80%以上,表明C/SiC复合材料的韧性断裂行为受到了严重的破坏。

表 1 1800℃热处理前后C/SiC复合材料的力学性能 Table 1 Mechanical properties of the C/SiC composites before and after 1800℃ annealing
SampleDensity/
(g·cm-3)
Flexural
strength/
MPa
Fracture
toughness/
(MPa·m1/2)
Mass loss
rate/%
CSC12001.96±0.27473±4126.7±1.60.00
CSC18001.84±0.3277.4±183.01±1.18.43

图1是1800℃热处理前后C/SiC复合材料的载荷-位移曲线。可知,试样CSC1200具有较高的抗弯强度、模量以及较好的韧性:线性OA段说明复合材料在出现显著微观失效前为线弹性;A点由于基体中垂直纤维轴向裂纹的扩展,导致复合材料模量变小,B点出现纤维断裂,因此,AB段中基体裂纹逐渐发展到饱和状态;而BC段复合材料载荷的维持,主要来源于界面的脱粘、纤维断裂和拔出,直至材料失效。对于CSC1800,不仅其抗弯强度和模量下降,而且呈现典型的脆性断裂。

图 1 1800℃热处理前后C/SiC复合材料的载荷-位移曲线 Fig.1 Load-displacement curves of C/SiC composites before and after 1800℃ annealing

图2是1800℃热处理前后C/SiC复合材料断口的SEM照片。可以清楚地看到,1800℃热处理前后C/SiC复合材料断口的微观形貌发生了显著的变化:在试样CSC1200的断口中(图2(a)),基体比较致密,纤维拔出比较长,而且基体与纤维存在界面解离、裂纹偏转等现象(箭头所指),说明此试样的基体-纤维界面结合强度比较适中,因此,复合材料具有较高的断裂强度和韧性,呈现韧性断裂行为[12,13];在试样CSC1800的断口中(图2(b)),基体存在较多缺陷,纤维几乎没有拔出,说明此试样的基体-纤维界面结合强度比较高,同时纤维受到损伤,强度下降,因此,裂纹扩展过程中直接穿过纤维,复合材料呈现脆性断裂行为[8]

图 2 1800℃热处理前后C/SiC复合材料断口的SEM照片 (a)CSC1200;(b)CSC1800 Fig.2 SEM images of the fracture surfaces of the C/SiC composites before and after 1800℃ annealing (a)CSC1200;(b)CSC1800

从以上分析可知,在1800℃高温环境中,C/SiC复合材料发生了一系列物理和化学变化。图3是1800℃热处理前后C/SiC复合材料中相邻两纤维中心之间的EDS谱图。从曲线可知,在试样CSC1200中(图3(a)),氧元素分布在基体-纤维界面处,为两个谱峰,说明氧元素在界面处富集[14, 15];在试样CSC1800中(图3(b)),氧元素基本消失,说明在C/SiC复合材料中发生了如下碳热还原反应[15, 16],与表1中复合材料具有较大失重率的现象相符。

图 3 1800℃热处理前后C/SiC复合材料中相邻两纤维中心之间的EDS谱图 (a)CSC1200;(b)CSC1800 Fig.3 EDS spectra between the centers of two close fibers in the C/SiC composites before and after 1800℃ annealing (a)CSC1200;(b)CSC1800

图4是1800℃热处理后C/SiC复合材料界面结构的TEM图。可以看到,1800℃热处理后,在C/SiC复合材料界面处生长了较大的SiC晶粒,尺寸大于200nm(图4(a));纤维和基体的结晶程度增加,都呈微晶结构,同时两者之间界限不清(图4(b)),表明纤维和基体之间为化学结合,原因是高温环境中碳热还原反应和硅元素扩散。这些现象都说明,在1800℃热处理过程中,C/SiC复合材料的界面结构发生不可逆变化,炭纤维受到较大损伤,因此,1800℃热处理后C/SiC复合材料的力学性能急剧下降[17]

图 4 1800℃热处理后C/SiC复合材料界面结构的TEM图 (a)低倍;(b)高倍 Fig.4 TEM images of the interface microstructures of the C/SiC composites after 1800℃ annealing (a)low magnification;(b)high magnification
3 结论

(1)在1800℃热处理过程中,PIP法C/SiC复合材料的界面处发生碳热还原反应和硅扩散,导致基体和纤维之间产生化学结合,纤维受到损伤。

(2)1800℃热处理后,PIP法C/SiC复合材料出现8%的失重率;力学性能急剧下降,幅度达到80%以上;韧性断裂行为受到严重破坏,转变为脆性断裂模式。

参考文献(References)
[1] NASLAIN R. Design,preparation and properties of non-oxide CMCs for application in engines and nuclear reactors:an overview[J]. Composites Science and Technology,2004,64(2):155-170.
[2] PAPENBRUG U, BEYER S, LAUBE H, et al. Advanced ceramic matrix composites(CMC'S) for space propulsion system. Virginia:American Institute of Aeronautics and Astronautics,1997.
[3] BEYER S, STROBEL F. Development and testing of C/SiC composites for liquid rocket propulsion applications[R]. Virginia:American Institute of Aeronautics and Astronautics,1999.
[4] ZIEGLER G, RICHTER I, SUTTOR D. Fiber-reinforced composites with polymer-derived matrix:processing,matrix formation and properties[J]. Composites Part A,1999,30(4):411-417.
[5] HERWOOD W J, WHITMARSH C K, JACOBS J M, et al. Low cost,near-net shape ceramic composites using resin transfer molding and pyrolysis(RTMP)[J]. Ceramic Engineering and Science Proceedings,1996,17(4):174-183.
[6] ODESHI A G, MUCHA H, WIELAGE B. Manufacture and characterization of a low cost carbon fibre reinforced C/SiC dual matrix composite[J]. Carbon,2006,44(2):1994-2001.
[7] JULIANE M, MARCUS M, MEINHARD K, et al. New porous silicon carbide composite reinforced by intact high-strength carbon fibres[J]. Journal of the European Ceramic Society,2006,26(4):1715-1722.
[8] MA Y, WANG S, CHEN Z. Effects of high-temperature annealing on the microstructures and mechanical properties of Cf/SiC composites using polycarbosilane[J]. Materials Science and Engineering:A,2011,528(7-8):3069-3072.
[9] MA Y, CHEN Z. Effects of 1600 ℃ annealing atmosphere on the microstructures and mechanical properties of C/SiC composites fabricated by precursor infiltration and pyrolysis[J]. Ceramics International,2012,38(5):4229-4235.
[10] 张立同, 成来飞. 连续纤维增韧陶瓷基复合材料可持续发展战略探讨[J].复合材料学报,2007,24(2):1-6. ZHANG L T, CHENG L F. Discussion on strategies of sustainable development of continuous fiber reinforced ceramic matrix composites[J]. Acta Materiae Compositae Sinica,2007,24(2):1-6.
[11] ZHOU C C, CHANG C R, HU H F, et al. Preparation of 3D-Cf/SiC composites at low temperatures[J]. Materials Science and Engineering:A,2008,488(1-2):569-572.
[12] JIAN K, CHEN Z, MA Q, et al. Effects of pyrolysis process on the microstructures and mechanical properties of Cf/SiC composites using polycarbosilane[J]. Materials Science and Engineering:A,2005,390(1):154-158.
[13] 周长城, 张长瑞, 胡海峰, 等. C/SiC 复合材料的低温制备工艺研究[J]. 材料工程,2012,(9):44-47. ZHOU C C, ZHANG C R, HU H F, et al. Preparation of C/SiC composites at low temperature[J]. Journal of Materials Engineering,2012,(9):44-47.
[14] MA Y, WANG S,CHEN Z. In situ growth of a carbon interphase between carbon fibres and a polycarbosilane-derived silicon carbide matrix[J]. Carbon,2011,49(8):2869-2872.
[15] JIANG X X, BRYDSON R, APPLEYARD S P, et al. Characterization of the fibre-matrix interfacial structure in carbon fibre-reinforced polycarbosilane-derived SiC matrix composites using STEM/EELS[J]. Journal of Microscopy,1999,196(2):203-212.
[16] LY H Q, TAYLOR R,DAY R. Conversion of polycarbosilane(PCS) to SiC-based ceramic:part II pyrolysis and characterization[J]. Journal of Materials Science,2001,36(16):4045-4057.
[17] DESPRÉS J F,MONTHIOUX M. Mechanical properties of C/SiC composites as explained from their interfacial features[J]. Journal of the European Ceramic Society,1995,15(3):209-224.