Availableonlineatwww.sciencedirect.cor ° Science Direct CERAMICS INTERNATIONAL ELSEVIER Ceramics International 33 (2007)1395-1398 www.elsevier.com/locate/ceramint Short communication Unidirectional carbon fiber and Sic particulate Co-reinforced fused silica composite G H. Zhou a, b S W. Wang a, * X.X. Huang a. J.K. Guo a Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China Received 8 September 2005: received in revised form 3 March 2006: accepted 14 April 2006 Available online 25 September 2006 Abstract Unidirectional carbon fiber (uni-Cr) reinforced fused silica composite with the addition of 20 wt %o SiC particulate(SiCp)(uni-CH SiO2+ 20 wt% SiCp) was prepared by slurry infiltration and hot-pressing. The room temperature mechanical properties were investigated and the fracture features of composites were observed. While the flexural strength parallel to the fiber direction decreased from 667.3 to 431.8 MPa, that of perpendicular to the fiber direction increased from 18.0 to 54.3 MPa for uni-C /SiO, composite after the addition of SiCp. Obviously, the anisotropy of mechanical properties was strongly modified. The increased flexural strength might be ascribed to the increase of the fiber/matrix interfacial bonding strength caused by the SiCp addition C 2006 Elsevier Ltd and Techna Group S.r. l. All rights reserved Keywords: B. Composites; C Mechanical properties; D. Glass ceramics; D. SiC; Fused silica 1. Introduction in mechanical properties. That is, flexural strength parallel to the fiber direction was up to 600 MPa. However, its strength In the area of space lightweight structural materials, carbon perpendicular to the fiber direction was lower than 20 MPa In fiber reinforced glass matrix composites have demonstrated a 1990s, Han et al. prepared a fused silica matrix composite wide range of attributes which include high strength, high reinforced by chopped carbon fiber and si3N4, BN particle [9- stiffness, excellent toughness, low density, unique wear 11]. Though mechanical properties of this composite did not resistance, and environmental stability for structural applica- show anisotropy, a flexural strength of 73.2 MPa was obtained tions [1-4]. Fused silica is one of the glass matrix material for and the reinforced effort was far from being comparable with heat shields and space lightweight structural applications those of fiber yarn [8, 12]. The present work was undertaken to cm), low coefficient of thermal expansion (CTE), low forced SiO2 composite (uni-C/SiO2)with the addition of thermal conductivity, high softening temperature and excel- submicron SiC particulate (SiCp). The mechanical properties lent chemical inertness [5,6]. However, monolithic fused and microstructure of the hot-pressed composites were silica is rarely used due to its intrinsic brittleness and very low investigated. The toughening mechanism of the composite mechanical properties [7]. In 1970s, Guo et al. studied the was discussed unidirectional carbon fiber reinforced fused silica glass composite. The results showed its flexural strength was 12- 2. Experimental procedures fold that of fused silica, its impact strength was upgraded by 40-fold, and its work of fracture was increased by three orders Fused silica powder (SiO2 >99 wt %o pure, and average of magnitude [8]. However, this composite showed anisotropy particle size around 2.8 um), PAN-based carbon fit (2800 MPa average tensile strength, and 6-7 um in diameter), and silicon carbide powder (a-Sic >98 wt. pure, and Corresponding author. Tel: +86 21 52414320 fax: +86 21 52413903. average particle size around 0.5 um) were used as starting ang51@ mail sic ac cn(S.w. Wang) naterials. The powders were mixed in deionized water with 2-8842/$3200C 2006 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016 1-ceramint.2006.04008
Short communication Unidirectional carbon fiber and SiC particulate Co-reinforced fused silica composite G.H. Zhou a,b , S.W. Wang a, *, X.X. Huang a , J.K. Guo a a Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, PR China b Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China Received 8 September 2005; received in revised form 3 March 2006; accepted 14 April 2006 Available online 25 September 2006 Abstract Unidirectional carbon fiber (uni-Cf) reinforced fused silica composite with the addition of 20 wt.% SiC particulate (SiCp) (uni-Cf/ SiO2 + 20 wt.% SiCp) was prepared by slurry infiltration and hot-pressing. The room temperature mechanical properties were investigated and the fracture features of composites were observed. While the flexural strength parallel to the fiber direction decreased from 667.3 to 431.8 MPa, that of perpendicular to the fiber direction increased from 18.0 to 54.3 MPa for uni-Cf/SiO2 composite after the addition of SiCp. Obviously, the anisotropy of mechanical properties was strongly modified. The increased flexural strength might be ascribed to the increase of the fiber/matrix interfacial bonding strength caused by the SiCp addition. # 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; C. Mechanical properties; D. Glass ceramics; D. SiC; Fused silica 1. Introduction In the area of space lightweight structural materials, carbon fiber reinforced glass matrix composites have demonstrated a wide range of attributes which include high strength, high stiffness, excellent toughness, low density, unique wear resistance, and environmental stability for structural applications [1–4]. Fused silica is one of the glass matrix material for heat shields and space lightweight structural applications because of its prominent properties such as low density (2.2 g/ cm3 ), low coefficient of thermal expansion (CTE), low thermal conductivity, high softening temperature and excellent chemical inertness [5,6]. However, monolithic fused silica is rarely used due to its intrinsic brittleness and very low mechanical properties [7]. In 1970s, Guo et al. studied the unidirectional carbon fiber reinforced fused silica glass composite. The results showed its flexural strength was 12- fold that of fused silica, its impact strength was upgraded by 40-fold, and its work of fracture was increased by three orders of magnitude [8]. However, this composite showed anisotropy in mechanical properties. That is, flexural strength parallel to the fiber direction was up to 600 MPa. However, its strength perpendicular to the fiber direction was lower than 20 MPa. In 1990s, Han et al. prepared a fused silica matrix composite reinforced by chopped carbon fiber and Si3N4, BN particle [9– 11]. Though mechanical properties of this composite did not show anisotropy, a flexural strength of 73.2 MPa was obtained and the reinforced effort was far from being comparable with those of fiber yarn [8,12]. The present work was undertaken to modify the anisotropy of unidirectional carbon fiber reinforced SiO2 composite (uni-Cf/SiO2) with the addition of submicron SiC particulate (SiCp). The mechanical properties and microstructure of the hot-pressed composites were investigated. The toughening mechanism of the composite was discussed. 2. Experimental procedures Fused silica powder (SiO2 >99 wt.% pure, and average particle size around 2.8 mm), PAN-based carbon fiber (2800 MPa average tensile strength, and 6–7 mm in diameter), and silicon carbide powder (a-SiC >98 wt.% pure, and average particle size around 0.5 mm) were used as starting materials. The powders were mixed in deionized water with www.elsevier.com/locate/ceramint Ceramics International 33 (2007) 1395–1398 * Corresponding author. Tel.: +86 21 52414320; fax: +86 21 52413903. E-mail address: swwang51@mail.sic.ac.cn (S.W. Wang). 0272-8842/$32.00 # 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2006.04.008
G.H. Zhou et al. /Ceramics International 33(2007)1395-1398 carboxymethyl cellulose( CMC) as a binder and isopropyl alcohol as a dispersant, and then ball-milled with agate balls The prepreg was prepared by infiltrating the continuous carbon Fiber Bundle Failure fiber into the slurry and then dried, stacked in a graphite die and hot-pressed at 1350C and 20 MPa in a N2 atmosphere. For omparison, fused silica and unidirectional carbon fiber reinforced fused silica composites were also prepared. The t content of carbon fiber was approximately 30 vol %o in the Zigzag composites Density measurements were performed based on Archi medes principle. The specimens were machined into bars of 36 mm x 4 mm x 3 mm to measure the flexural strength by the three-point bending method with a span of 30 mm and a cocracking cross-head speed of 0.5 mm/min at room temperature (RT in air. Single-edge notched-beam (SENB) samples were 0000.250.50 fabricated by notching the segments of tested flexure specimens nt/m with a 0.20 mm thick diamond wafering saw. The Fig. 1. Load-displacement curves: (a) uni-CHSiO2 and (b) uni-Cr 30 mm x 6 mm x 3 mm SENB samples were tested in SiOz+ 20wt% SiCE three-point loading with a span of 24 mm and a cross-head speed of 0.05 mm/min Fracture toughness Kic was calculated from 18.0 to 54.3 MPa, and the fracture toughness also had a by the AsTme 399-74 formula[ 13]. The flexural strength and slight increase from 20.1 to 21.9 MPa m". This is because the the fracture toughness measurements were conducted viscosity of fused silica increased Instron-1195 testing machine. Five specimens were tested for would retard the process of densification at the same sintering each sample. The fracture surface of composite was observed temperature Density measurements showed the relative density y electron probe X-ray microanalyser(EPMA, JXA-8100). (R D )of uni-CuSiO2 composite was 97.6%. However, R.D. of The microstructural features of interface were examined using uni-C/SiO2 +20 wt %o SiCp composite was 95.0%. The lower transmission electronic microscope (TEM, Model 200CX, R D. was responsible for the decrease of flexural JEOL, Japan). parallel to the fiber direction for uni-CHSiO2+20 wt. omposite. On the other hand, the increase of flexural st 3. Results and discussion perpendicular to the fiber direction may be attributed to the enhancement of the fiber/matrix interfacial bonding strength by Table I is the mechanical properties of several SiO2-based the addition of SiCp, which was similar to the case of 10 vol composites. Enhanced by unidirectional carbon fiber, the chopped CrSiOz+ 5 vol. Si3N4 composite [14] flexural strength and the fracture toughness of the hot-pressed Fig. la and b show the typical load-displacement curves of fused silica increased from 54.8 to 667.3 MPa and 1.0 to uni-CrSiO2 and uni-Cr/SiO2+ 20 wt SiCp composites, 20.1 MPa m"parallel to the fiber direction(Cr), respectively. respectively. With the increase of the load, the two samples Nevertheless, the flexural strength of uni-C.SiO2 composite exhibit elastic response in the initial stage, and then a deviation was only 18.0 MPa perpendicular to the fiber direction (1C+). appears at a load of about 170 MPa, indicating occurrence of Parallel to the fiber direction, the reinforcing effect of C was microcracking in the matrix. After that, the second elastic significant and the continuous fiber played an important role in response appears up to the maximum load where a significant carrying the load. On the contrary, perpendicular to the fiber drop in load occurs, which is attributed to fiber bundle failure. direction, there was no Cr to carry the load and the interstices The final stage is the non-linear region-the tail of curve, between carbon fibers resulted in the decrease of the revealing fiber pull-out, bridging, and sliding [6, 15. There are mechanical properties, to values lower than the matrix itself. two differences in the load-displacement curves of the two After SiCp addition, it was seen that though the flexural strength samples. Firstly, the second elastic response of uni-CrSio parallel to the fiber direction decreased from 667 3 to composite is smooth(Fig. la), whereas, that of uni-CH 431.8 MPa, that perpendicular to the fiber direction increased SiO2+ 20 wt SiCp composite is zigzag, which is ascribed to Table 1 Properties of SiOz-based composites Properties Hot-pressed Uni-C小SiO2 Uni-C/SiO2+ 20 wt% SiC 10 vol %o chopped CH fused silica SiO2+5vol%SiN4[14】 2.02 2.15 Flexural strength(MPa) 6673±33.9(C ±283(|Cp 73 180±20(⊥Cr Fracture toughness, KIc(MPa m 1.0 20.1±2.0(|C 219±14(|C 2.4
carboxymethyl cellulose (CMC) as a binder and isopropyl alcohol as a dispersant, and then ball-milled with agate balls. The prepreg was prepared by infiltrating the continuous carbon fiber into the slurry and then dried, stacked in a graphite die and hot-pressed at 1350 8C and 20 MPa in a N2 atmosphere. For comparison, fused silica and unidirectional carbon fiber reinforced fused silica composites were also prepared. The content of carbon fiber was approximately 30 vol.% in the composites. Density measurements were performed based on Archimedes principle. The specimens were machined into bars of 36 mm 4 mm 3 mm to measure the flexural strength by the three-point bending method with a span of 30 mm and a cross-head speed of 0.5 mm/min at room temperature (RT) in air. Single-edge notched-beam (SENB) samples were fabricated by notching the segments of tested flexure specimens with a 0.20 mm thick diamond wafering saw. The 30 mm 6 mm 3 mm SENB samples were tested in three-point loading with a span of 24 mm and a cross-head speed of 0.05 mm/min. Fracture toughness KIC was calculated by the ASTME 399-74 formula [13]. The flexural strength and the fracture toughness measurements were conducted by Instron-1195 testing machine. Five specimens were tested for each sample. The fracture surface of composite was observed by electron probe X-ray microanalyser (EPMA, JXA-8100). The microstructural features of interface were examined using transmission electronic microscope (TEM, Model 200CX, JEOL, Japan). 3. Results and discussion Table 1 is the mechanical properties of several SiO2-based composites. Enhanced by unidirectional carbon fiber, the flexural strength and the fracture toughness of the hot-pressed fused silica increased from 54.8 to 667.3 MPa and 1.0 to 20.1 MPa m1/2 parallel to the fiber direction (jjCf), respectively. Nevertheless, the flexural strength of uni-Cf/SiO2 composite was only 18.0 MPa perpendicular to the fiber direction (?Cf). Parallel to the fiber direction, the reinforcing effect of Cf was significant and the continuous fiber played an important role in carrying the load. On the contrary, perpendicular to the fiber direction, there was no Cf to carry the load and the interstices between carbon fibers resulted in the decrease of the mechanical properties, to values lower than the matrix itself. After SiCp addition, it was seen that though the flexural strength parallel to the fiber direction decreased from 667.3 to 431.8 MPa, that perpendicular to the fiber direction increased from 18.0 to 54.3 MPa, and the fracture toughness also had a slight increase from 20.1 to 21.9 MPa m1/2. This is because the viscosity of fused silica increased after SiCp addition, which would retard the process of densification at the same sintering temperature. Density measurements showed the relative density (R.D.) of uni-Cf/SiO2 composite was 97.6%. However, R.D. of uni-Cf/SiO2 + 20 wt.% SiCp composite was 95.0%. The lower R.D. was responsible for the decrease of flexural strength parallel to the fiber direction for uni-Cf/SiO2 + 20 wt.% SiCp composite. On the other hand, the increase of flexural strength perpendicular to the fiber direction may be attributed to the enhancement of the fiber/matrix interfacial bonding strength by the addition of SiCp, which was similar to the case of 10 vol.% chopped Cf/SiO2 + 5 vol.% Si3N4 composite [14]. Fig. 1a and b show the typical load–displacement curves of uni-Cf/SiO2 and uni-Cf/SiO2 + 20 wt.% SiCp composites, respectively. With the increase of the load, the two samples exhibit elastic response in the initial stage, and then a deviation appears at a load of about 170 MPa, indicating occurrence of microcracking in the matrix. After that, the second elastic response appears up to the maximum load where a significant drop in load occurs, which is attributed to fiber bundle failure. The final stage is the non-linear region—the tail of curve, revealing fiber pull-out, bridging, and sliding [6,15]. There are two differences in the load–displacement curves of the two samples. Firstly, the second elastic response of uni-Cf/SiO2 composite is smooth (Fig. 1a), whereas, that of uni-Cf/ SiO2 + 20 wt.% SiCp composite is zigzag, which is ascribed to 1396 G.H. Zhou et al. / Ceramics International 33 (2007) 1395–1398 Table 1 Properties of SiO2-based composites Properties Hot-pressed fused silica Uni-Cf/SiO2 Uni-Cf/SiO2 + 20 wt.% SiCp 10 vol.% chopped Cf/ SiO2 + 5 vol.% Si3N4 [14] Density (g/cm3 ) 2.17 2.02 2.10 2.15 Flexural strength (MPa) 54.8 667.3 33.9 (jjCf) 431.8 28.3 (jjCf) 73.2 18.0 2.0 (?Cf) 54.3 1.9 (?Cf) Fracture toughness, KIC (MPa m1/2) 1.0 20.1 2.0 (jjCf) 21.9 1.4 (jjCf) 2.40 Fig. 1. Load–displacement curves: (a) uni-Cf/SiO2 and (b) uni-Cf/ SiO2 + 20 wt.% SiCp.
G.H. Zhou et al./Ceramics international 33(2007)1395-1398 1397 b 20. Oky x300 10um wD11mm 28.kV x310m11m Fig. 2. The morphology of fracture surface: (a) uni-CHSiO2 and(b)uni-C/SiO,+20 wt %o SiC microcracking induced by the mismatch of the thermal composite was higher than that of uni-CrSiOz+ 20 wt %o SiCp expansion coefficients(CTE) between SiCp and the SiOz composite. In the light of interface theory of ceramic matrix atrix [6, 15, 16]. This microcracking also resulted in the composites( CMCs), strong fiber/matrix interfacial bonding decrease of flexural strength parallel to the fiber direction after results in the matrix microcracks propagating through the fiber iCp addition. The second difference is the non-linear region- with the increase of load. Thus, the fibers are easily broken the tail of load-displacement curves. The tail length of uni-C+ Whereas, in the case of weak fiber/matrix interfacial bonding Sio2 composite is longer than that of uni-CHSiO2+ 20 wt %o the matrix microcracks propagate along the weak interface, SiCp composite. These two differences would be further which results in the fiber/matrix interface debonding. Conse discussed in the next part quently, fibers are easily pulled out. According to the fiber pull Typical fractographs of the composite are shown in Fig. 2. out lengths, it can be concluded that the fiber/matrix interfacial Without SiCp addition( Fig 2a), extensive fiber pull-out was bonding of uni-CrSiOz+ 20 wt %o Sicp composite was observed in the fracture surface, and accompanying with very stronger than that of uni-CiSiO2 composite, which might be large pull-out lengths. While, fiber pull-out was short after SiCp related to the fiber/matrix interfacial sliding stress addition(Fig. 2b). Therefore, the different tail lengths in the Thouless et al. [17] reported that the distribution in fiber ad-displacement curves resulted for the two samples, pull-out lengths in unidirectional CMCs should be related respectively. Fiber pull-out lengths can also explain why fiber/matrix interfacial sliding stress, fiber diameter, and flexural strength(parallel to the fiber direction) of uni-C/SiO2 Weibull modulus of the fiber. Presently, fiber/matrix interfacial SiOz Matrix Fig 3. The transmission electron micrographs of composites:(a) uni-C!SiO2 and(b) uni-CHSiO2+ 20 wt. SiC
microcracking induced by the mismatch of the thermal expansion coefficients (CTE) between SiCp and the SiO2 matrix [6,15,16]. This microcracking also resulted in the decrease of flexural strength parallel to the fiber direction after SiCp addition. The second difference is the non-linear region— the tail of load–displacement curves. The tail length of uni-Cf/ SiO2 composite is longer than that of uni-Cf/SiO2 + 20 wt.% SiCp composite. These two differences would be further discussed in the next part. Typical fractographs of the composite are shown in Fig. 2. Without SiCp addition (Fig. 2a), extensive fiber pull-out was observed in the fracture surface, and accompanying with very large pull-out lengths. While, fiber pull-out was short after SiCp addition (Fig. 2b). Therefore, the different tail lengths in the load–displacement curves resulted for the two samples, respectively. Fiber pull-out lengths can also explain why flexural strength (parallel to the fiber direction) of uni-Cf/SiO2 composite was higher than that of uni-Cf/SiO2 + 20 wt.% SiCp composite. In the light of interface theory of ceramic matrix composites (CMCs), strong fiber/matrix interfacial bonding results in the matrix microcracks propagating through the fiber with the increase of load. Thus, the fibers are easily broken. Whereas, in the case of weak fiber/matrix interfacial bonding, the matrix microcracks propagate along the weak interface, which results in the fiber/matrix interface debonding. Consequently, fibers are easily pulled out. According to the fiber pullout lengths, it can be concluded that the fiber/matrix interfacial bonding of uni-Cf/SiO2 + 20 wt.% SiCp composite was stronger than that of uni-Cf/SiO2 composite, which might be related to the fiber/matrix interfacial sliding stress. Thouless et al. [17] reported that the distribution in fiber pull-out lengths in unidirectional CMCs should be related to the fiber/matrix interfacial sliding stress, fiber diameter, and Weibull modulus of the fiber. Presently, fiber/matrix interfacial G.H. Zhou et al. / Ceramics International 33 (2007) 1395–1398 1397 Fig. 2. The morphology of fracture surface: (a) uni-Cf/SiO2 and (b) uni-Cf/SiO2 + 20 wt.% SiCp. Fig. 3. The transmission electron micrographs of composites: (a) uni-Cf/SiO2 and (b) uni-Cf/SiO2 + 20 wt.% SiCp
G.H. Zhou et al. /Ceramics International 33(2007)1395-1398 liding stress should play an important role in the fiber pull-out [2] D. C. Phillips, R.A. Sambell, D. Bowen, The mechanical properties of lengths. Fig. 3a and b show microstructures at the fiber/matrix carbon fiber reinforced Pyrex glass, J. Mater. Sci. 7(1972)1454-1464. interface for these two samples. Without SiC, addition 3I R.A. Sambell, D.H. Bowen, D.C. Phillips, Carbon fiber composites with (Fig. 3a), the fiber/matrix interface is clear but a pore is 972)676681 entrapped. On the other hand, partial Sicp were sandwiched [4] D.C. Phillips, Interfacial bonding and the toughness of carbon fiber into the fiber/matrix interface in the SiCp added sample reinforced glass and glass-ceramics, J Mater. Sci. 9(1974)1847-1854 (Fig. 3b). The interfacial sliding stress caused by SiCp at the 5IT. Vasilis, T Erturk, R Ambati SCS-6 SiC hiber reinforced fused silica fiber/matrix interface enhanced the interfacial bonding strength (6) D.C. Jia, Y.Zhou, T.Q. Lei, Ambient andelevated temperature mechanical nd retarded the slippage. As a result, during flexural test, the roperties of hot-pressed fused silica matrix composite, J. Eur. Ceram. subtle effect of interface sliding stress among SiO2 matrix, Sicp Soc.23(2003)801-808 and carbon fibers resulted in the zigzag curve of the second [7] Q. Yu, Materials Technology, Series of Missiles and Spaceflight-Mate- elastic response and an increase of flexural strength perpend rials and Technology(Lower), Publishing House of Aerospace, Beijing. cular to the fiber direction 1993.pp.1-215 [8] J K. Guo, T.S. Yan, Microstructure and Properties of Ceramic Materials, Science Press, Beijing, 1984, Pp. 281-289 4. Conclusions [9] H.Q. Han, Microstructure and properties of several Sio2 matrix c Is Thesis, Harbin Institute of Technology. Harbin, 1995. pp (1) Uni-C/SiO and uni-C.SiO2+20 wt% SiCp composites [10] J.J. Yao, B.S. Li, X.X. Huang, J.K. Guo, Mechanical properties and its were prepared by slurry infiltration and hot-pressing. A ening mechanisms in SiO2-Si, N4 composite, J Inorg. Mater. 12(1) (1997)47-53 flexural strength of 667.3 MPa and fracture toughness of [11] G.W. Wen, G L Wu, T Q Lei, et al. Co-enhanced Sioz-BN ceramics for 20. 1 MPa m"parallel to the fiber direction for the uni-C+ high temperature dielectric applications, J. Eur. Ceram. Soc. 20(2000) Sio2 was attributed to the fiber pull-out. 1923-1928 (2)The flexural strength perpendicular to the fiber direction [12] G.T. Wu, Exploratory research on the applications of carbon fiber rein- increased from 18.0 to 54.3 MPa after the addition of sic forced silica on the thermal-protective structure of satellite and aero-ship pace Mater. Technol. 4(1991)72-78. The anisotropy of mechanical properties was strongly [131 Z.D. Guan, Z.T. Zhang J.S. Jiao, The Physical Properties of Inorganic modified for the uni-C/SiOz composite. Materials, Tsinghua University Publishing Company, 1992, p. 59. ()The dispersion of SiCp might enhance the interfacial sliding [14] H.Q. Han, QL Ge, T.Q. Lei, et al., The properties of fused silica increase of the fiber/matrix interfacial bonding strength and >/AG.Eales, Powder Metall.Technol.17(3)(1999)201-204 stress at the fiber/matrix interface which contributed to the e of fiber rein. forced ceramic matrix composites, high temperature/high perfo the flexural strength perpendicular to the fiber direction omposites, in: F.D. Lemkey, S.G. Fishman, et al. (Eds ) Mat. Res Soc symp.Poc,vol.120.1988,pp.213-24 16] H. Zhao, Z.Z. Jin, The analysis of residual stress and toughening mechan- References isms of particulate reinforced dual-phase ceramics, J Chin. Ceram. Soc 24(10)(1996)491-497 1] K.M. Prewo, J.J. Brennan, G.K. Layden, Fiber reinforced glasses and [17 M D. Thouless. O. Sbaizero, L.S. Sigl, A G. Evans, Effect of interface lass-ceramics for high performance applications, Ceram. Bull. 65(2) echanical properties on pullout in a SiC-fiber-reinforced LAS glass- (1986)305-313. ceramics, J. Am. Ceram Soc. 72(4)(1989)525-532
sliding stress should play an important role in the fiber pull-out lengths. Fig. 3a and b show microstructures at the fiber/matrix interface for these two samples. Without SiCp addition (Fig. 3a), the fiber/matrix interface is clear but a pore is entrapped. On the other hand, partial SiCp were sandwiched into the fiber/matrix interface in the SiCp added sample (Fig. 3b). The interfacial sliding stress caused by SiCp at the fiber/matrix interface enhanced the interfacial bonding strength and retarded the slippage. As a result, during flexural test, the subtle effect of interface sliding stress among SiO2 matrix, SiCp and carbon fibers resulted in the zigzag curve of the second elastic response and an increase of flexural strength perpendicular to the fiber direction. 4. Conclusions (1) Uni-Cf/SiO2 and uni-Cf/SiO2 + 20 wt.% SiCp composites were prepared by slurry infiltration and hot-pressing. A flexural strength of 667.3 MPa and fracture toughness of 20.1 MPa m1/2 parallel to the fiber direction for the uni-Cf/ SiO2 was attributed to the fiber pull-out. (2) The flexural strength perpendicular to the fiber direction increased from 18.0 to 54.3 MPa after the addition of SiCp. The anisotropy of mechanical properties was strongly modified for the uni-Cf/SiO2 composite. (3) The dispersion of SiCp might enhance the interfacial sliding stress at the fiber/matrix interface, which contributed to the increase of the fiber/matrix interfacial bonding strength and the flexural strength perpendicular to the fiber direction. References [1] K.M. Prewo, J.J. Brennan, G.K. Layden, Fiber reinforced glasses and glass-ceramics for high performance applications, Ceram. Bull. 65 (2) (1986) 305–313. [2] D.C. Phillips, R.A. Sambell, D. Bowen, The mechanical properties of carbon fiber reinforced Pyrex glass, J. Mater. Sci. 7 (1972) 1454–1464. [3] R.A. Sambell, D.H. Bowen, D.C. Phillips, Carbon fiber composites with ceramic and glass matrices. Part 2. Continuous fibers, J. Mater. Sci. 7 (1972) 676–681. [4] D.C. Phillips, Interfacial bonding and the toughness of carbon fiber reinforced glass and glass-ceramics, J. Mater. Sci. 9 (1974) 1847–1854. [5] T. Vasilos, T. Ertu¨rk, R. Ambati, SCS-6 SiC fiber reinforced fused silica composites, Ceram. Eng. Sci. Proc. 14 (9–10) (1993) 962–995. [6] D.C. Jia, Y. Zhou, T.Q. Lei, Ambient and elevated temperature mechanical properties of hot-pressed fused silica matrix composite, J. Eur. Ceram. Soc. 23 (2003) 801–808. [7] Q. Yu, Materials Technology, Series of Missiles and Spaceflight—Materials and Technology (Lower), Publishing House of Aerospace, Beijing, 1993, pp. 1–215. [8] J.K. Guo, T.S. Yan, Microstructure and Properties of Ceramic Materials, Science Press, Beijing, 1984, pp. 281–289. [9] H.Q. Han, Microstructure and properties of several SiO2 matrix composites, MS Thesis, Harbin Institute of Technology, Harbin, 1995, pp. 47–50. [10] J.J. Yao, B.S. Li, X.X. Huang, J.K. Guo, Mechanical properties and its toughening mechanisms in SiO2–Si3N4 composite, J. Inorg. Mater. 12 (1) (1997) 47–53. [11] G.W. Wen, G.L. Wu, T.Q. Lei, et al., Co-enhanced SiO2–BN ceramics for high temperature dielectric applications, J. Eur. Ceram. Soc. 20 (2000) 1923–1928. [12] G.T. Wu, Exploratory research on the applications of carbon fiber reinforced silica on the thermal-protective structure of satellite and aero-ship, Aerospace Mater. Technol. 4 (1991) 72–78. [13] Z.D. Guan, Z.T. Zhang, J.S. Jiao, The Physical Properties of Inorganic Materials, Tsinghua University Publishing Company, 1992, p. 59. [14] H.Q. Han, Q.L. Ge, T.Q. Lei, et al., The properties of fused silica composites, Powder Metall. Technol. 17 (3) (1999) 201–204. [15] A.G. Evans, D.B. Marshall, The mechanical performance of fiber reinforced ceramic matrix composites, high temperature/high performance composites, in: F.D. Lemkey, S.G. Fishman, et al. (Eds.), Mat. Res. Soc. Symp. Proc., vol. 120, 1988, pp. 213–246. [16] H. Zhao, Z.Z. Jin, The analysis of residual stress and toughening mechanisms of particulate reinforced dual-phase ceramics, J. Chin. Ceram. Soc. 24 (10) (1996) 491–497. [17] M.D. Thouless, O. Sbaizero, L.S. Sigl, A.G. Evans, Effect of interface mechanical properties on pullout in a SiC-fiber-reinforced LAS glassceramics, J. Am. Ceram. Soc. 72 (4) (1989) 525–532. 1398 G.H. Zhou et al. / Ceramics International 33 (2007) 1395–1398