Materials and Design 30(2009)3738-3742 Contents lists available at Science Direct Material Materials and design Design ELSEVIER journalhomepagewww.elsevier.com/locate/matdes Influence factors of C/C-Sic dual matrix composites prepared by reactive melt infiltration Jiang Si-Zhou, Xiong Xiang, Chen Zhao-Ke, Xiao Peng, Huang Bai-Yun State Key Lab for Powder Metallurgy, Central South University, Changsha 410083, China ARTICLE INFO A BSTRACT The effects of the type of carbon matrix, the infiltration temperature and high temperature treatment eceived 24 September 2008 (HTT) on the infiltration behavior of molten Si and preparation of C/c-Sic dual matrix composites have cepted 9 February 2009 Available online 21 February 2009 been investigated. The results showed that: Resin carbon matrix is benificial to the infiltration of molten Si than pyrolysis carbon matrix. 1650C is more suitable for the infiltration of molten Si in porous C/Cpre- forms than 1550C. The high infiltration depth at 1650C is responsible for the high density of C/c-Sic composites. hTt facilitates to the infiltration of molten Si and the formation of more SiC. High density matrix composites and low open porosity C/C-Sic dual matrix composites can be prepared by optimal reactive mol E Mechanical tration method. The flexural strength, elastic modul and impact toughness of up to 265.4 MPa, 28.1 GPa and 28.5 kJ/m respectively. Heat treatment at 2300C decreases the es flexural strength, elastic modul and impact toughness, but improve the fracture behavior of C/c-Sic e 2009 Elsevier Ltd. All rights reserved. 1 Introduction on temperature and high temperature treatment(hTr) on the infiltration behavior of molten Si and the preparation of C/c-Sic C/c composites are the most promiseful brake disc materials for composites will be investigated in detail. In addition, in the rMI are susceptible to oxidation at elevated temperatures, and ease to failure of rupture. Therefore, the mechanical properties of C/c-Sic failure in humidity environment [1-3]. Carbon fiber reinforce opposites had been also discussed arbon and Sic dual matrix composites, namely C/c-SiC comp ites, of many advantages such as low density, good mechanical 2. Experimental procedures and tribological properties, good thermal properties, good oxida- tion and erosion resistance, can survive in severe service 2.1. Raw materials conditions of aviation and space missions. Compared to C/c com- posites, C/C-SiC composites have less change for high temperature To prepare porous C/c preforms with resin carbon matrix or failures. Therefore, as novel friction and wear materials, C/C-Sic pyrolysis carbon matrix, PAN carbon fibre needled felt with a den omposites have been considered to have wide application pros- sity of 0.6 g/cm Furan resin with a viscosity of 40-150 MPas(at pect[4-9. 25C), C3H6 and N2, were used as preform, impregnant, VD car Reactive melt infiltration(RMI)is one of the successful methods bon source and dilute gas respectively. In RMI process, silicon pow- to prepare C/C-SiC composites Compared to other processes such ders of 99% purity and 75 um in diameter were used as Si source to slurry hot pressure, polymer infiltration pyrolysis and chemica prepare C/c-Sic dual matrix com vapor deposition(CVD), RMI possesses many advantages including short fabrication period, low cost, near net shape, low porosity, etc. 2.2. Materials preparation [10-12 and has recently become a commercialized method of 2. 2.1. Preparation of porous C/C preforms However, to prepare C/C-SiC composites by RMi, the influence Pan carbon fibre needled felts are used as preforms. The carbon factor and infiltration behavior of molten Si may be very complex. fiber was PAN-based(T300, 12k, Toray, Japan). The needled felts In this article, the influence of the type of carbon matrix, the infiltra- were prepared by the three-dimensional needling technique, start ing with repeatedly overlapping the layers of 0 non-woven fiber ding author.Tel:+867318836079:fax:+867318836079 cloth, short-cut-fiber web, and 90 non-woven fiber cloth with address:Xiong228@sina.com(Xxiang). needle-punching step by step. 0261-3069/s- see front matter o 2009 Elsevier Ltd. All rights reserved. do:101016/ mates2009020
Influence factors of C/C–SiC dual matrix composites prepared by reactive melt infiltration Jiang Si-Zhou, Xiong Xiang *, Chen Zhao-Ke, Xiao Peng, Huang Bai-Yun State Key Lab for Powder Metallurgy, Central South University, Changsha 410083, China article info Article history: Received 24 September 2008 Accepted 9 February 2009 Available online 21 February 2009 Keywords: A. Ceramic matrix composites B. Fabrics E. Mechanical abstract The effects of the type of carbon matrix, the infiltration temperature and high temperature treatment (HTT) on the infiltration behavior of molten Si and preparation of C/C–SiC dual matrix composites have been investigated. The results showed that: Resin carbon matrix is benificial to the infiltration of molten Si than pyrolysis carbon matrix. 1650 C is more suitable for the infiltration of molten Si in porous C/C preforms than 1550 C. The high infiltration depth at 1650 C is responsible for the high density of C/C–SiC composites. HTT facilitates to the infiltration of molten Si and the formation of more SiC. High density and low open porosity C/C–SiC dual matrix composites can be prepared by optimal reactive molten infiltration method. The flexural strength, elastic modul and impact toughness of C/C–SiC composites are high up to 265.4 MPa, 28.1 GPa and 28.5 kJ/m2 respectively. Heat treatment at 2300 C decreases the composites flexural strength, elastic modul and impact toughness, but improve the fracture behavior of C/C–SiC dual matrix composites. 2009 Elsevier Ltd. All rights reserved. 1. Introduction C/C composites are the most promiseful brake disc materials for applications in military and civilian aircrafts. Unfortunately, they are susceptible to oxidation at elevated temperatures, and ease to failure in humidity environment [1–3]. Carbon fiber reinforced carbon and SiC dual matrix composites, namely C/C–SiC composites, of many advantages such as low density, good mechanical and tribological properties, good thermal properties, good oxidation and erosion resistance, can survive in severe service conditions of aviation and space missions. Compared to C/C composites, C/C–SiC composites have less change for high temperature failures. Therefore, as novel friction and wear materials, C/C–SiC composites have been considered to have wide application prospect [4–9]. Reactive melt infiltration (RMI) is one of the successful methods to prepare C/C–SiC composites. Compared to other processes such as slurry hot pressure, polymer infiltration pyrolysis and chemical vapor deposition (CVD), RMI possesses many advantages including short fabrication period, low cost, near net shape, low porosity, etc. [10–12] and has recently become a commercialized method of great market competition. However, to prepare C/C–SiC composites by RMI, the influence factor and infiltration behavior of molten Si may be very complex. In this article, the influence of the type of carbon matrix, the infiltration temperature and high temperature treatment (HTT) on the infiltration behavior of molten Si and the preparation of C/C–SiC composites will be investigated in detail. In addition, in the RMI process, one may degrade carbon fibers, leading to a catastrophic failure of rupture. Therefore, the mechanical properties of C/C–SiC composites had been also discussed. 2. Experimental procedures 2.1. Raw materials To prepare porous C/C preforms with resin carbon matrix or pyrolysis carbon matrix, PAN carbon fibre needled felt with a density of 0.6 g/cm3 , Furan resin with a viscosity of 40–150 MPa s (at 25 C), C3H6 and N2, were used as preform, impregnant, CVD carbon source and dilute gas respectively. In RMI process, silicon powders of 99% purity and 75 lm in diameter were used as Si source to prepare C/C–SiC dual matrix composites. 2.2. Materials preparation 2.2.1. Preparation of porous C/C preforms PAN carbon fibre needled felts are used as preforms. The carbon fiber was PAN-based (T300, 12k, Toray, Japan). The needled felts were prepared by the three-dimensional needling technique, starting with repeatedly overlapping the layers of 0 non-woven fiber cloth, short-cut-fiber web, and 90 non-woven fiber cloth with needle-punching step by step. 0261-3069/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.02.013 * Corresponding author. Tel.: +86 731 8836079; fax: +86 731 8836079. E-mail address: Xiong228@sina.com (X. Xiang). Materials and Design 30 (2009) 3738–3742 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes
J. Si-Zhou et al Materials and Design 30(2009)3738-3742 Porous C/c preforms with Resin carbon matrix or pyrolysis car- results are showed in Table 1. For resin carbon matrix, the density bon matrix were prepared by impregnation and carbonization(IC) of composites is high with low porosity. For pyrolysis carbon ma- process or CVD respectively. IC process was consisting of three trix, the density is relative lower with slight larger porosity. uran resin impregnation in preforms, solidification at The main reason for higher density of C/c-SiC composites with oC for 1 h, and carbonization at 800-1000C for 2 h. The resin carbon matrix is the easy infiltration and uniform distribu- al CVd was operated at 900-1150C with C3H6 as the tion of molten Si. the uniform distribution facilitate the reaction gas and N2 the dilute gas of molten Si with resin carbon. as a result, Sic was formed and uni- formly distributed in the composites(see in Fig. 1). 2. 2. 2. Preparation of c/c-Sic composites This can be testified by studying the morphology of SiC. The Porous c/C preforms were embedded in Si powders in morphologies of Sic in resin carbon matrix and pyrolytic carbon ite pot. The pot was then placed in a high temperature matrix are quite different(see in Fig. 2). For resin carbon matrix. urnace to prepare C/c-Sic dual matrix composites molten Si can flow into porous C/c preform easily and react with 1550C or 1650C for 1-2h. In infiltration process, the high tem- resin carbon to form a 2-7 um thick SiC layer. While for pyrolytic perature furnace was protected by inert gas at 1 atm pressure carbon matrix, molten Si can only react with pyrolytic carbon in In order to study the influence of HTT, porous C/c preforms with the outer layer. The obtained sic layer is thin and takes the original resin carbon matrix were treated at 2100-2300C for 2 h prior to morphology of pyrolytic carbon. Note that the infiltration process RMI process. of molten Si can be influenced by the different sic morphologies. In porous C/C preform with resin carbon matrix, the wetting angle 23. Characterization (0)changes from that between molten Si and solid C to that be- tween molten si and solid sic due to the formation of a continuous The density and open porosity of porous C/c preforms and c/c- SiC layer. Then the wetting angle is decreased with improved wet- SiC composites were measured according to Archimedes principle. ting performance. Therefore, the infiltration process of molten Samples with a size of 40 mmx5 mmx3 mm were used to test the will be enhanced accordingly. this is to say, Resin carbon matrix flexural strength by INSTRON CSS-44100 machine The gauge size is beneficial to the infiltration of molten St as 30 mm and the cross head speed was 0.5 mm/min The load- displacement curves were recorded by computer at the same time. 3. 2. The influence of temperature Film composition was analyzed by a D/max 2550 VB+18 kw rotating target X-ray diffraction(XRDanalyzer(Rigaku Ltd, Japan, Porous c/c preforms with resin carbon matrix were used to JEOL-6360LV scanning electron microscopy(SEM)with working of molten Si. The results were listed in Table 2. The infiltration of molten Si was difficult at 1550C and the composites were ended up with low relative density and high porosity(>12%).At 3. Results and discussion 1650C, the infiltration was successful with low porosity (a<5%) of the composites. 3. 1. The influence of carbon matrix Assuming the pore shape in porous C/C preform is cylinder and ignoring the ascending inertia force of molten To study the influence of carbon matrix on the infiltration established the infiltration equation [13-15]. behavior of molten si we conducted more tests at 1550C. the dh C20 Table 1 (1 Influence of carbon matrix on density and open porosity of C/c-Sic composites. Matrix Porous C/C preforms C/c-SiC composites where h denotes the infiltration height or depth in m: t the infiltra- (%)p2(gcm-3)a2(x) tion time in s: u the viscosity of molten Si in Pa S: o the surface tension of molten Si in N/m: 0 the wetting angle between molten esin carbon Pyrolysis carbon 1.34 .o 63.4 Si and solid; rt) the mean capillary radius at the time in m: g the ity in m s: p the density of I Si in g/cm. C is a factor te:P1 and Ey are the density and open porosity of porous C/C preforms: Pz and ez whose value is usually taken to be 1 /3, assuming isotropic porous are density and open porosity of C/C-SiC composites. Fig. 1. Microstructures of C/C-SiC composites with resin carbon matrix(a) inter-fiber and(b)inter-bundle
Porous C/C preforms with Resin carbon matrix or pyrolysis carbon matrix were prepared by impregnation and carbonization (IC) process or CVD respectively. IC process was consisting of three steps, Furan resin impregnation in preforms, solidification at 180–200 C for 1 h, and carbonization at 800–1000 C for 2 h. The isothermal CVD was operated at 900–1150 C with C3H6 as the reactant gas and N2 the dilute gas. 2.2.2. Preparation of C/C–SiC composites Porous C/C prerforms were embedded in Si powders in a graphite pot. The pot was then placed in a high temperature induction furnace to prepare C/C–SiC dual matrix composites at either 1550 C or 1650 C for 1–2 h. In infiltration process, the high temperature furnace was protected by inert gas at 1 atm pressure. In order to study the influence of HTT, porous C/C preforms with resin carbon matrix were treated at 2100–2300 C for 2 h prior to RMI process. 2.3. Characterization The density and open porosity of porous C/C preforms and C/C– SiC composites were measured according to Archimedes principle. Samples with a size of 40 mm5 mm3 mm were used to test the flexural strength by INSTRON CSS – 44100 machine. The gauge size was 30 mm and the cross head speed was 0.5 mm/min. The load– displacement curves were recorded by computer at the same time. Film composition was analyzed by a D/max 2550 VB+18 kW rotating target X-ray diffraction (XRD) analyzer (Rigaku Ltd., Japan, Cu Ka radiation, k = 1.54056 Å). Microstructure was analyzed by a JEOL-6360LV scanning electron microscopy (SEM) with working voltage of 25 kV. 3. Results and discussion 3.1. The influence of carbon matrix To study the influence of carbon matrix on the infiltration behavior of molten Si, we conducted more tests at 1550 C. The results are showed in Table 1. For resin carbon matrix, the density of composites is high with low porosity. For pyrolysis carbon matrix, the density is relative lower with slight larger porosity. The main reason for higher density of C/C–SiC composites with resin carbon matrix is the easy infiltration and uniform distribution of molten Si. The uniform distribution facilitate the reaction of molten Si with resin carbon. As a result, SiC was formed and uniformly distributed in the composites (see in Fig. 1). This can be testified by studying the morphology of SiC. The morphologies of SiC in resin carbon matrix and pyrolytic carbon matrix are quite different (see in Fig. 2). For resin carbon matrix, molten Si can flow into porous C/C preform easily and react with resin carbon to form a 2–7 lm thick SiC layer. While for pyrolytic carbon matrix, molten Si can only react with pyrolytic carbon in the outer layer. The obtained SiC layer is thin and takes the original morphology of pyrolytic carbon. Note that the infiltration process of molten Si can be influenced by the different SiC morphologies. In porous C/C preform with resin carbon matrix, the wetting angle (h) changes from that between molten Si and solid C to that between molten Si and solid SiC due to the formation of a continuous SiC layer. Then the wetting angle is decreased with improved wetting performance. Therefore, the infiltration process of molten Si will be enhanced accordingly. This is to say, Resin carbon matrix is beneficial to the infiltration of molten Si. 3.2. The influence of temperature Porous C/C preforms with resin carbon matrix were used to study the influence of temperatures on the infiltration behavior of molten Si. The results were listed in Table 2. The infiltration of molten Si was difficult at 1550 C and the composites were ended up with low relative density and high porosity (e > 12%). At 1650 C, the infiltration was successful with low porosity (e < 5%) of the composites. Assuming the pore shape in porous C/C preform is cylinder and ignoring the ascending inertia force of molten Si, Washburn has established the infiltration equation [13–15], dh dt ¼ C 8lh 2rcos h rðtÞ qgh rðtÞ 2 ð1Þ where h denotes the infiltration height or depth in m; t the infiltration time in s; l the viscosity of molten Si in Pa S; r the surface tension of molten Si in N/m; h the wetting angle between molten Si and solid; r(t) the mean capillary radius at the time in m; g the gravity in m/s2 ; q the density of molten Si in g/cm3 . C is a factor whose value is usually taken to be 1/3, assuming isotropic porous media. Table 1 Influence of carbon matrix on density and open porosity of C/C–SiC composites. Matrix Porous C/C preforms C/C–SiC composites Dq (%) q1 (g cm3 ) e1 (%) q2 (g cm3 ) e2 (%) Resin carbon 1.38 24.0 2.25 1.0 63.4 Pyrolysis carbon 1.34 19.5 2.04 3.9 52.2 Note: q1 and e1 are the density and open porosity of porous C/C preforms; q2 and e2 are density and open porosity of C/C–SiC composites. Fig. 1. Microstructures of C/C–SiC composites with resin carbon matrix (a) inter-fiber and (b) inter-bundle. J. Si-Zhou et al. / Materials and Design 30 (2009) 3738–3742 3739
J. Si-Zhou et al/ Materials and Design 30(2009)3738-3742 (b) Fig. 2. Morphology of SiC formed by the reaction of molten Si with different carbon matrix(a) resin carbon matrix and (b) pyrolytic carbon matrix. Table 2 Influence of temperature on density and open porosity of c/c-Sic composites. aperature(° C/C Porous preforms C/C-SiC composites 3 From Eq (1)we can see that the transport of molten Si is gov-a I-i Substituting typical parameters into Eq(o)一 erned by capillarity effect, the resistance of viscous, wetting angle, surface tension, gravity forces and the reaction between Si and C term on the right is at least two orders of magnitude less than the 1700 capillary term and therefore can be neglected 1600 The pore size of porous C/c preform will change with time c Time /s to the formation of SiC. The effect of chemical reaction on pore size Temperature /K can be represented as Fig 3. The depth of molten Si infiltrated into porous amorphous carbon preforms r()=0-Atl2 (r=100 um)as the function of time and temperature. where To is the original radius of pore: As is the temperature-depen- Agt/ the thickness of SiC layer The temperature-dependent coeffi- A=1/2D )3 Here De is the effective diffusivity: Mc, Msi, Pc and Psi the atomic- 05 tion h(t=0)=0, the infiltration depth allowed for chemical reac 日 tion, takes following form Time/s The infiltration kinetics depends on several factors: time, vis Radius/×105m Fig. 4. The relationship of infiltration height in porous carbon preforms tors are time dependent. The infiltration depth of molten Si (T=1823K) nce of hiT on density and open porosity of C/c-SiC composites. of porous C/C preforms Density increment percent(% Open porosity decrement percent (% Carbonized HTTed 2.38 75.0 HTT-high temperature treatment, 2100-2300C
From Eq. (1) we can see that the transport of molten Si is governed by capillarity effect, the resistance of viscous, wetting angle, surface tension, gravity forces and the reaction between Si and C. Substituting typical parameters into Eq. (1), the second (gravity) term on the right is at least two orders of magnitude less than the capillary term and therefore can be neglected. The pore size of porous C/C preform will change with time due to the formation of SiC. The effect of chemical reaction on pore size can be represented as rðtÞ ¼ r0 Adt 1=2 ð2Þ where r0 is the original radius of pore; Ad is the temperature-dependent coefficient to the time and Adt 1=2 the thickness of SiC layer formed by chemical reaction. The temperature-dependent coeffi- cient is defined as Ad ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2De MCqSi MSiqC s ð3Þ Here De is the effective diffusivity; MC, MSi, qC and qSi the atomic weight and density of C and Si respectively. Integrating the equation according to boundary (initial) condition h(t = 0) = 0, the infiltration depth allowed for chemical reaction, takes following form h ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Cr cos h 2l r0t 2 3 Adt 3=2 s ð4Þ The infiltration kinetics depends on several factors: time, viscosity, surface tension, and wetting angle. Except time, these factors are time dependent. The infiltration depth of molten Si in Fig. 2. Morphology of SiC formed by the reaction of molten Si with .different carbon matrix (a) resin carbon matrix and (b) pyrolytic carbon matrix. Table 2 Influence of temperature on density and open porosity of C/C–SiC composites. Temperature (C) C/C Porous preforms C/C–SiC composites q1 (g cm3 ) e1 (%) q2 (g cm3 ) e2 (%) 1550 1.47 16.9 1.67 12.3 1650 1.47 16.9 1.98 3.4 Table 3 Influence of HTT on density and open porosity of C/C–SiC composites. State of porous C/C preforms Porous C/C preforms C/C–SiC composites Density increment percent (%) Open porosity decrement percent (%) q1 (g cm3 ) e1 (%) q2 (g cm3 ) e2 (%) Carbonized 1.49 18.1 1.97 7.2 32.2 60.2 HTTed* 1.36 26.4 2.38 1.5 75.0 94.3 * HTT-high temperature treatment, 2100–2300 C. Fig. 3. The depth of molten Si infiltrated into porous amorphous carbon preforms (r = 100 lm) as the function of time and temperature. Fig. 4. The relationship of infiltration height in porous carbon preforms (T = 1823 K). 3740 J. Si-Zhou et al. / Materials and Design 30 (2009) 3738–3742
J. Si-Zhou et al Materials and Design 30(2009)3738-3742 2[(b) Fig. 5. Microstructures of C/c-Sic composites and the distribution of si element (a) low magnification, (b) high magnification of (a). C/c preform as function of infiltration temperature matrix and the ejection of volatilizable substances. Therefore, the vas presented in Fig 3. According to Fig 3, we can know filtration of molten Si has been improved by HIT. In Fig. 5, silicon h infiltration depth at 1650C is responsible for the is infiltrated in inter-fiber and inter-bundle pores in porous C/c density of C/c-Sic dual matrix composite preform with limited residual porosity(white phase shows the dis- tribution of Si element ). 3.3. The infiuence of HIT The influence of HTT on SiC contents in C/c-Sic dual matrix composites has also been studied. The detailed results are showed Porous c/c preforms with resin carbon matrix are again used to in Table 4. More Sic has formed after the porous C/C preforms ivestigate the influence of HrT on infiltration behavior of molten being HITed. The reaction activity of Si with C is mainly lies on Si at 1550oC and the results are listed in table 3 the type of carbon matrix, porosity or specific surface area of pore Being HrTed, the density of C/C-Sic dual matrix composites is and the temperature infiltration time of molten Si. However, the high up to 2.38 g cm with open porosity of 1.5%. Being carbor infiltration temperature and time are constant and not to be con- ized, the density is less than 2.0 g cm-3 with open porosity larger sidered here. In addition, molten Si will react with solid carbon than 7% immediately when they contact, then the successive reaction is According to Eq (1), the infiltration contents of Si(o)can be de- mainly controlled by the diffusion of Si and C in the formed Sic duced as layer. So, the influence of carbon matrix is limited and the reaction ivity is dominated by specific surface area of pores. In Fig. 6. a(cos o)rt (5) there are more pores or microcracks in hrTed resin carbon matrix nd the formation of ng to increasing specific surface area of pores In Eq (5), parameters of viscosity A, surface tension o, density p and infiltration time t of molten Si are constant. Since the wetting 3.4. The mechanical properties of g/c-Sic composites tration content of molten Si is then only a function of the capillary The mechanical properties of C/c-Sic composites are shown in The infiltration depth (or infiltration content) is with Table 5. As can be seen from Table 5. The flexural strength, elastic initial pore radius and infiltration time(see in Fig. treatment at 2300C are high up to 265.4 MPa, 28. 1 GPa and HTTed, the open porosity, especially the capillary forms has increased due to the volume shrinkage of resin carbon Table 5 The mechanical properties of C/c-SiC dual matrix composites. Table 4 Influence of HTT on Sic content of C/C-SiC composites Sample Flexural strength Impact toughness xx(K m-) State of porous C/C preforms C/C-SiC dual matrix composites P-SiC (% Residual si(‰) 2654 28 Fig. 6. Observation of C/C-Sic dual matrix composites after the infiltration of molten Si (a)resin carbon without HTT(b)resin carbon with HIT
porous C/C preform as function of infiltration temperature and time was presented in Fig. 3. According to Fig. 3, we can know that the high infiltration depth at 1650 C is responsible for the high density of C/C–SiC dual matrix composites. 3.3. The influence of HTT Porous C/C preforms with resin carbon matrix are again used to investigate the influence of HTT on infiltration behavior of molten Si at 1550 C and the results are listed in Table 3. Being HTTed, the density of C/C–SiC dual matrix composites is high up to 2.38 g cm3 with open porosity of 1.5%. Being carbonized, the density is less than 2.0 g cm3 with open porosity larger than 7%. According to Eq. (1), the infiltration contents of Si (x) can be deduced as x ¼ qp ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rðcos hÞr5t 2l s ð5Þ In Eq. (5), parameters of viscosity l, surface tension r, density q and infiltration time t of molten Si are constant. Since the wetting angle is in the range of 0–20 and can be neglected here, the infiltration content of molten Si is then only a function of the capillary radius r. The infiltration depth (or infiltration content) is increased with initial pore radius and infiltration time (see in Fig. 4). After being HTTed, the open porosity, especially the capillary radius of preforms has increased due to the volume shrinkage of resin carbon matrix and the ejection of volatilizable substances. Therefore, the infiltration of molten Si has been improved by HTT. In Fig. 5, silicon is infiltrated in inter-fiber and inter-bundle pores in porous C/C preform with limited residual porosity (white phase shows the distribution of Si element). The influence of HTT on SiC contents in C/C–SiC dual matrix composites has also been studied. The detailed results are showed in Table 4. More SiC has formed after the porous C/C preforms being HTTed. The reaction activity of Si with C is mainly lies on the type of carbon matrix, porosity or specific surface area of pores, and the temperature, infiltration time of molten Si. However, the infiltration temperature and time are constant and not to be considered here. In addition, molten Si will react with solid carbon immediately when they contact, then the successive reaction is mainly controlled by the diffusion of Si and C in the formed SiC layer. So, the influence of carbon matrix is limited and the reaction activity is dominated by specific surface area of pores. In Fig. 6, there are more pores or microcracks in HTTed resin carbon matrix than carbonized, leading to increasing specific surface area of pores and the formation of more SiC. 3.4. The mechanical properties of C/C–SiC composites The mechanical properties of C/C–SiC composites are shown in Table 5. As can be seen from Table 5. The flexural strength, elastic modul and impact toughness of C/C–SiC composites before heat treatment at 2300 C are high up to 265.4 MPa, 28.1 GPa and Fig. 5. Microstructures of C/C–SiC composites and the distribution of Si element (a) low magnification, (b) high magnification of (a). Table 4 Influence of HTT on SiC content of C/C–SiC composites. State of porous C/C preforms C/C–SiC dual matrix composites b-SiC (%) Residual Si (%) Carbonized 33.8 23.1 HTTed 59.8 25.1 Fig. 6. Observation of C/C–SiC dual matrix composites after the infiltration of molten Si (a) resin carbon without HTT (b) resin carbon with HTT. Table 5 The mechanical properties of C/C–SiC dual matrix composites. Sample Flexural strength Impact toughness ak (KJ m2 ) rb (MPa) Eb (GPa) 1 265.4 28.1 28.5 2 108.4 24.0 16.1 Sample 1: C/C–SiC dual matrix composites before heat treatment; Sample 2: C/C– SiC dual matrix composites after heat treatment. J. Si-Zhou et al. / Materials and Design 30 (2009) 3738–3742 3741
J. Si-Zhou et al/ Materials and Design 30(2009)3738-3742 than pyrolysis carbon matrix. 1650C is more suitable for the infill- tration of molten Si in porous C/C preforms than 1550C HTT facil itates to the infiltration of molten si and the formation of more sic High density and low open porosity C/C-Sic dual matrix compos- ites can be prepared by optimal reactive molten infiltration meth od. The flexural strength, elastic modul and imp C-SiC composites are high up to 265. 4 MPa, 28.1 GPa and 28.5 kJ/ respectively. Heat treatment at 2300C decreases the compo ites flexural strength, elastic modul and impact toughness, but im- prove the fracture behavior of C/c-Sic dual matrix composites. Ac This research work is supported by National Natural oundation of China under the grant No. 50872154 and by Creative research group of National Natural Science Foundation of China 0.0 04 under the grant no. 50721003 References Fig. 7. Stress-strain curve of C/c-Sic dual matrix composites Fitzer E. The future of the carbon composites Carbon 1987: 25: 163-90. 28.5 k/m" respectively. Heat treatment at 2300C decreases the summary composites flexural strength, elastic modul and impact toughness to 108.4 MPa, 24.1 GPa and 16.1 k /m- respectively. However, heat (TSC) like C/C, C/SiC, and Sic/siC composites. Adv Eng Mater 2002: 4: 903-1 treatment can improve the fracture behavior of C/c-Sic dual [4] Krenkel W. Berndt F C/C-SiC comp for space applications and advanced natrix composites. The typical stress-strain curve of C/c-Sic dual [51 Cambell T Ting ]. Avitabile P, Min]. Dynamic properties of 3-D reinforced C/Sic matrix composites after heat treatment at 2300C is shown in the rs-2200 liner aerospike engine Ceram Eng Sci Proc 2000: 21: 5 [6I Muehlra non-linear rise and flat displacement, corresponding to three [71 Wang LS, Xiong X, Xiao P Effect of manufacturing techniques of preforms c stress-strain curve can be divided into three segments: linear rise, properties and fracture modes of C/c-SiC composites. Chin J Nonferrous stages: matrix elastic deformation, matrix crack and fiber pull out respectively. When the displacement reaches the maximum [8 Wang LS, Xiong X, Xiao P. Influence of high-temperature processing and different carbon matrixes on behaviour of infiltration of liquid silicon into value, the composites fail completely. After heat treatment at us cC preforms. Min Metall Eng 2003: 23: 77-9 2300C, C/c-Sic dual matrix composites show typical"pseudo- [91 Wang LS, Xiong X, ductility"fracture behavior. In addition, further research about 10 Krenkel W. cost effective 12003:21:37-41 of composites by melt infiltration the hit process must be pursued to get the C/c-Sic dual matrix 22:443-54. composites with high strength and high toughness. by melt infiltration. Am Ceram Soc Bull [12] Rajesh 4. Conclusions og g se 4a bies during reactive melt infiltration Transp Porous Media Based on the study of the influence of infiltration temperature [13 Yang J. llegbusi O. Kinetics of silicon-metal infiltration into porous carbon. anuf2000:31:617-25 different porous C/c performs and HTT on the infiltration behavior [14] Washburn EW. The dynamics of capi of molten Si and preparation of c/C-Sic dual matrix composites by [151 Rhim Wk, ohsaka k. Thermophy active melt infiltration, we can make the following conclusion, specific heat capacity. emissivity, surface tension and viscosity. J Cryst Growth Resin carbon matrix is beneficial to the infiltration of molten si 2000:208:313-21
28.5 kJ/m2 respectively. Heat treatment at 2300 C decreases the composites flexural strength, elastic modul and impact toughness to 108.4 MPa, 24.1 GPa and 16.1 kJ/m2 respectively. However, heat treatment can improve the fracture behavior of C/C–SiC dual matrix composites. The typical stress–strain curve of C/C–SiC dual matrix composites after heat treatment at 2300 C is shown in Fig. 7. The fracture behavior shows ‘elastic–plastic’ manners. The stress–strain curve can be divided into three segments: linear rise, non-linear rise and flat displacement, corresponding to three stages: matrix elastic deformation, matrix crack and fiber pullout respectively. When the displacement reaches the maximum value, the composites fail completely. After heat treatment at 2300 C, C/C–SiC dual matrix composites show typical ‘‘pseudoductility” fracture behavior. In addition, further research about the HTT process must be pursued to get the C/C–SiC dual matrix composites with high strength and high toughness. 4. Conclusions Based on the study of the influence of infiltration temperature, different porous C/C performs and HTT on the infiltration behavior of molten Si and preparation of C/C–SiC dual matrix composites by reactive melt infiltration, we can make the following conclusion, Resin carbon matrix is beneficial to the infiltration of molten Si than pyrolysis carbon matrix. 1650 C is more suitable for the infiltration of molten Si in porous C/C preforms than 1550 C. HTT facilitates to the infiltration of molten Si and the formation of more SiC. High density and low open porosity C/C–SiC dual matrix composites can be prepared by optimal reactive molten infiltration method. The flexural strength, elastic modul and impact toughness of C/ C–SiC composites are high up to 265.4 MPa, 28.1 GPa and 28.5 kJ/ m2 respectively. Heat treatment at 2300 C decreases the composites flexural strength, elastic modul and impact toughness, but improve the fracture behavior of C/C–SiC dual matrix composites. Acknowledgements This research work is supported by National Natural Science Foundation of China under the Grant No. 50872154 and by Creative research group of National Natural Science Foundation of China under the Grant No. 50721003. References [1] Fitzer E. The future of the carbon/carbon composites. Carbon 1987;25:163–90. [2] Windhorst T, Blount G. Carbon/carbon composites; a summary of recent developments and applications. Mater Des 1997;18:11–5. [3] Christin F. Design, fabrication, and application of thermostructural composites (TSC) like C/C, C/SiC, and SiC/SiC composites. Adv Eng Mater 2002;4:903–12. [4] Krenkel W, Berndt F. C/C–SiC composites for space applications and advanced friction systems. Mater Sci Eng A 2005;412:177–81. [5] Cambell T, Ting J, Avitabile P, Min J. Dynamic properties of 3-D reinforced C/SiC for the RS-2200 liner aerospike engine. Ceram Eng Sci Proc 2000;21:517–24. [6] Muehlratzer A. Production, properties and applications of ceramic matrix composites. CFI-Ceram Forum Int Ber Dtsch Keram Ges 1999;76:30–5. [7] Wang LS, Xiong X, Xiao P. Effect of manufacturing techniques of preforms on properties and fracture modes of C/C–SiC composites. Chin J Nonferrous Metal 2003;13:1196–201. [8] Wang LS, Xiong X, Xiao P. Influence of high-temperature processing and different carbon matrixes on behaviour of infiltration of liquid silicon into porous C/C preforms. Min Metall Eng 2003;23:77–9. [9] Wang LS, Xiong X, Xiao P. Factors affecting properties of C/C–SiC composites prepared by reactive melt infiltration. Powder Metall Technol 2003;21:37–41. [10] Krenkel W. Cost effective processing of composites by melt infiltration (LSI2Process). Ceram Eng Sci Proc 2001;22:443–54. [11] Hillig WB. Making ceramic composites by melt infiltration. Am Ceram Soc Bull 1994;73:56–62. [12] Rajesh G, Bhagat RB. Infiltration of liquid metals in porous compacts: modeling of permeabilities during reactive melt infiltration. Transp Porous Media 1999;36:43–68. [13] Yang J, Ilegbusi OJ. Kinetics of silicon-metal infiltration into porous carbon. Compos A: Appl Sci Manuf 2000;31:617–25. [14] Washburn EW. The dynamics of capillary flow. Phys Rev 1921;17:273–83. [15] Rhim WK, Ohsaka K. Thermophysical properties measurement of molten silicon by high-temperature electrostatic levitator: density, volume expansion, specific heat capacity, emissivity, surface tension and viscosity. J Cryst Growth 2000;208:313–21. 0.0 0.2 0.4 0.6 0.8 20 40 60 80 100 120 Fig. 7. Stress–strain curve of C/C–SiC dual matrix composites. 3742 J. Si-Zhou et al. / Materials and Design 30 (2009) 3738–3742
