- Email: [email protected]
SiC composites
Journal of the European Ceramic Society xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Short communication
Significance of modification of slurry infiltration process for the precursor impregnation and pyrolysis process of SiCf/SiC composites Shiv Singha,b,1,*, Jie Yinc,1, Lun Fengd, Dehi Pada Mondalb, Daejong Kime, Sea-Hoon Leea,** a
Division of Powder/Ceramics Research, Korea Institute of Materials Science, Changwon 641-831, Republic of Korea Lightweight Metallic Materials, Council of Scientific and Industrial Research-Advanced Materials and Processes Research Institute, Habibganj Naka, Hoshangabad Road, Bhopal, Madhya Pradesh 462026, India c State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 65049, China d Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO, USA e Nuclear Materials Development Division, Korea Atomic Energy Research Institute, Daejeon 305-353, Republic of Korea b
ARTICLE INFO
ABSTRACT
Keywords: Ceramic-matrix composites Infiltration Polymer precursor Silicon carbide Cold isostatic pressing
Several intermediate steps were applied before the precursor infiltration and pyrolysis process to improve the infiltration of SiC slurry for promoting the infiltration of SiC slurry into fiber voids. These steps include sonication, popping, electrophoretic deposition, vacuum infiltration and cold isostatic pressing (CIP). The intermediate processes, especially popping and CIP, had a beneficial effect on green density enhancement and improving the homogeneous infiltration of the slurry into fiber fabrics. The density of the SiCfiber/SiCfiller green body was 2.20 g/cm3, which corresponded to 68 % of relative density. The SiCf/SiC composite has a high density of 2.65 g/cm3 after seven PIP cycles.
1. Introduction Ceramic matrix composites (CMCs), particularly silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites, have been extensively used for high temperature and/or high-velocity environment including a nuclear reactor, rocket motor nozzles, aerospace applications, brake disk, semi-conductor industries, etc. [1–5]. SiCf/SiC composites possess superior characteristics over conventional metallic alloys and monolithic ceramics such as low density, thermodynamic stability, noteworthy creep/wear resistance, corrosion and oxidation resistance as well as excellent damage tolerance against adverse conditions [4,6,7]. There are numerous processes depending on the shape, size along with fabrication cost for developing SiC CMC composites. Chemical vapor infiltration (CVI), precursor infiltration and pyrolysis (PIP), liquid silicon infiltration, hot pressing and chemical liquid–vapor deposition are a few of them [7–9]. Among all routes, PIP is a relatively inexpensive process for the fabrication of multi-layered SiCf/SiC composites [7,9–11]. Nevertheless having aforesaid advantages, long processing time and large void spaces between fibers even after several PIP
cycles, along with the shrinkage cracking during pyrolysis are the main hurdles of this process [12]. In this context, several intermediate steps for promoting the infiltration of SiC slurry in between fibers have been incorporated before polymer infiltration in order to make composites of high green density and least porosity including low-pressure SiC slurry infiltration, ultra-sonication and electrophoretic deposition (EPD) [12–16]. In EPD, conscientious selection of SiC slurry concentration and optimized electric field provide a densely packed SiC green body which further help in the densification of SiCf/SiC composite [12]. In spite of the development of slurry infiltration processes described above, the nonhomogeneous infiltration of the slurry in between the fiber fabrics has been reported [12–16]. As a consequence, it is very important to understand the effects of each process and to develop alternative efficient processes. The purpose of current study is to investigate the effects of intermediate steps for promoting slurry infiltration in between fibers, such as the preparation of highly concentrated nano-SiC slurry, spreading and popping process of the woven fiber fabrics, EPD, vacuum/pressure infiltration along with cold isostatic pressing (CIP) processes, on the density, microstructure and mechanical strength of SiCf/SiC CMC
⁎ Corresponding author at: Lightweight Metallic Materials, Council of Scientific and Industrial Research-Advanced Materials and Processes Research Institute, Habibganj Naka, Hoshangabad Road, Bhopal, Madhya Pradesh 462026, India ⁎⁎ Corresponding author at: Division of Powder/Ceramics Research, Korea Institute of Materials Science, Changwon 641-831, Republic of Korea E-mail addresses: [email protected], [email protected] (S. Singh), [email protected] (S.-H. Lee). 1 Equal contribution.
https://doi.org/10.1016/j.jeurceramsoc.2020.01.009 Received 11 September 2019; Received in revised form 23 December 2019; Accepted 3 January 2020 0955-2219/ © 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: Shiv Singh, et al., Journal of the European Ceramic Society, https://doi.org/10.1016/j.jeurceramsoc.2020.01.009
Journal of the European Ceramic Society xxx (xxxx) xxx–xxx
S. Singh, et al.
fabricated via PIP process.
were prepared for reference purposes. All the processes were carried out for unpopped samples except popping.
2. Experimental details
2.3. Fabrication of SiCf/SiC composite via PIP and property analysis
2.1. Materials
A detailed description is given in supporting information. In brief, after completely drying the preform at 110 °C, the weight and volume of the SiCfiber/SiCfiller green body were measured in order to calculate the bulk density, and the samples were put inside the graphite molds. After pouring a significant amount of PCS and applying a vacuum for the infiltration of the liquid precursor into the green body, the samples were pressed by a tungsten plate (∼10 kg) using solid graphite punch [18]. Cross-linking was performed at 250 °C for 30 min and pyrolysis was done at 1400 °C for 2 h at a heating rate 5 °C and 1.5 °C, respectively. The whole analysis was accomplished in an argon atmosphere at atmospheric pressure. Seven cycles of PIP were executed to increase the density of SiCf/SiC composites.
Complete details are provided in the Supplementary information. 2.2. Pretreatment of SiC woven fabrics and slurry infiltration As received plane weaved SiC fiber fabrics were cut into 10 × 10 cm2 pieces and dipped into the de-ionized water. Ultra-sonication was performed for the expansion of plane-woven SiC fiber fabrics and consequent separation of individual fibers in the bundles using ultra sonicator (Sonics & Materials, USA) for 2 h. After drying at 105 °C for 12 h, pyrolytic carbon (PyC) coating (∼200 nm) was deposited by isothermal CVI at 1000 °C. The mixture of propane and hydrogen gas (molar ratio 6:1) was used as a carbon source and carrier gas, respectively for 50 min inside the reaction chamber. Next to CVI, PyC coated samples were cut into small pieces (3 × 3 cm2) for the novel popping process. The popping process was carried out in a thick wall stainless steel vessel with a variable air pressure of 0–1.0 MPa. After holding this pressure for 1 min, the lid of the vessel was opened forcefully for further expansion of SiC fibers using the rapid expansion of the gases in between the fibers. After this step, the optimization of the dispersion of SiC, prepared by high energy milling, was performed, which was described elsewhere in detail [17]. The dispersion of nano SiC (d50: 50 nm) (Fig. S1) was optimized as follows: 10 wt % of the nano SiC powder was dispersed with 10 wt% of different dispersants by ball milling at 200 r.p.m. (revolution per minute) for 12 h and subsequently by sonication for 30 min. Six dispersants (PEI-1000/5000/10000/300000, KV5068 and KV-9056) were tested with ethyl alcohol as the dispersoid. In some cases, ethyl alcohol was mixed with methyl ethyl ketone (MEK) (34:66 by weight ratio) in order to check the possibility of enhancing the dispersion behavior. The viscosity of 10 wt% slurry at 25 °C and the size distribution of the powder were determined using a viscometer (HB DV-II + pro, Brookfield Engineering Laboratories, MA, USA) and laser diffraction particle size analyzer (Coulter LS 13 320, Beckman Coulter Inc., Fl, USA), respectively. EPD was carried out for fifteen layers of fiber fabrics at an electrical field of 7.0 V for 10 min using 10 wt% nano SiC (d50: 50 nm) slurry. A probe sonicator was used in the whole process to improve the dispersion of SiC powder (VCX750, Sonics and Materials, CT, USA). A special type of EPD set-up was used where 7 SiC fabrics were separately put in one bath for EPD, i.e EPD was done individually for 15 fabrics. Vacuum/pressure infiltration was carried out using fifteen layers of processed SiC fabric. SiC powder with relatively large size (d50: 170 nm) prepared by the aforementioned mechanical alloying (MA) process was used to make 55 vol% slurry for infiltration. 1 wt% of PEI was used as a dispersant [17]. Multi-layered SiCf samples were put in a cylindrical vessel (chamber size = 4 × 4 × 1 cm3). Low pressure was created inside the chamber using a vacuum pump. Thereafter, a low vacuum chamber was filled with concentrated SiC slurry. Owing to low pressure, slurry penetrated very smoothly into a chamber and infiltrated in between SiC fiber fabrics. Subsequently, the chamber was pressurized with argon gas up to ∼0.15 MPa for enhancing the infiltration of SiC slurry. The pressure was released after 1 min. These vacuum and pressurization processes were repeated twice. Subsequent to this process, CIP was carried out for 15 min at 50 MPa pressure before the drying of the slurry. Subsequently, the samples were dried at 105 °C for 12 h. All the steps involved in the fabrication of composite are shown in Fig. 1. Some samples were also prepared using only sonication (expansion), popping, EPD or CIP in order to know the advantages of individual processes. However, vacuum infiltration was common for all the aforementioned samples. Also, unpopped samples
3. Results and discussion 3.1. Properties of SiC fiber fabrics The morphology of SiC fiber fabrics before and after sonication is displayed in Fig. 2. As-received SiC fabrics have significant void spaces in between the woven fiber bundles (Fig. 2a–a’). In contrast, the SiC fiber bundles which undergone ultra-sonication for 2 h were expanded in the fabrics significantly as shown in Fig. 2(b–b’). As a consequence, the voids in between the woven fiber bundles were filled. This expansion facilitates slurry infiltration in between fibers. Sonication was done before CVI to prevent possible damage to the PyC coating during sonication. PyC layer was deposited on the SiC fiber fabrics via isothermal CVI as shown in Fig. 2. PyC layer deposited on SiCf was smooth, uniform and continuous. The PyC coating partly closed the channels in between the fibers (Fig. 2(c)). Consequently, the slurry could not easily infiltrate into the pores in between the fibers. The thickness of PyC coating on the SiC fibers was 200 nm (Fig. 2 (c’)). 3.2. Densification of SiC fiber preform via slurry infiltration As shown in Fig. 3(a), primarily the loading of SiC filler increased up-to certain pressure (0.4 MPa) limit then it decreased with further pressure increase (Fig. S2). In order to understand the effect of PyC coating thickness on the optimum popping pressure, SiC fiber fabrics with a PyC coating thickness of 350 nm were prepared and tested (Fig. 3(b)). A similar mass change was observed with those shown in Fig. 3(a) except for the shift of optimum pressure from 0.4 MPa to 0.6 MPa, indicating that the optimum popping pressure increased with the increase of PyC coating thickness. The adjacent fibers are closely attached in unpopped samples (Fig. 3(d)). The popping process (0.6 MPa) separated the connected PyC coatings of the adjacent fibers (Fig. 3(c), and left marks on the surface of the coatings. The coatings began to be partially detached from the fiber surface. The separation of the PyC coating promoted the infiltration of the slurry into the pores between the fibers. However, when the popping pressure exceeded a certain value (1.0 MPa), the coating was mostly detached from the fiber surface in some areas (Fig. 3(e)). Because the electrical conduction of the SiC fiber was mainly performed by the PyC coating, the electrical conductivity of the fabrics decreased above the optimum popping pressure, which decreased the efficiency of the EPD process. Most of the pores of SiC fiber preform were filled with SiC filler during EPD process. Subsequent to EPD, vacuum/pressure infiltration was carried out using 55 vol% slurry for fifteen layers of the stacked fabrics in order to fill macropores between the fiber fabrics. The slurry infiltration technique was also responsible for reducing the number of PIP cycles because most of the macropores of the preform were partly filled before PIP. Vacuum infiltration of concentrated SiC slurry was performed to the 2
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Fig. 1. Schematic of steps involved in the fabrication SiCf/SiC composite.
stacked fabrics treated using different processes to understand the effects of each process on the infiltration of the SiC slurry (Fig. S3). These samples were tabulated in Table S1. In the expansion-CIP process condition, CIP of stacked fifteen layers of SiCf/SiC preform was performed under 50 MPa pressure immediately after vacuum/pressure infiltration, and before the increase of slurry viscosity by drying, in order to squeeze out extra SiC slurry from the fiber fabrics and further promoting the infiltration of the slurry. This process also facilitated in compact packing of SiCfiber/SiCfiller preform by applying high pressure to the preform, which reduced the thickness of prepared samples. Each process promoted the infiltration of the slurry. Especially, the beneficial effect of the popping and CIP process was clearly observed in Figs. S3(b) and (d), respectively. Fig. 4(a–b’) shows a cross-sectional micrograph of densified SiCfiber/ SiCfiller samples after the application of fiber expansion, popping, EPD and CIP at different resolutions before PIP. The void spaces in between the fibers/bundles are mostly filled by the aforementioned techniques used in the preparation of SiCfiber/SiCfiller samples. The SiC fillers, used during EPD and vacuum/pressure infiltration, were dispersed uniformly in the SiC fiber preform. The bulk density of prepared material was 2.20 g/cm3 after the drying of the sample, which corresponded to the relative density of 68 %. The micrographs of prepared polished SiCf/SiC CMCs are shown in Fig. 4(c–d’) after seven PIP cycles. The microstructures reveal that SiC matrices are uniformly and densely covered the empty spaces and pores in between the fibers. However, at some places, pores are observed owing to the incomplete filling of SiC filler during the slurry infiltration process. The free spaces in between the fibers and fibers bundles have been significantly filled by PCS after PIP, which is corroborated to high impregnation efficiency and relatively
small volume shrinkage occurred in the conversion of PCS [19]. The surface area of the CMC fabricated with and without popping was 13.91 and 14.19 m2/g and their porosity was 20.66 and 21.0 %, respectively. The SiCf/SiC CMC fabricated using the optimum conditions had a high density of 2.65 g/cm3 after seven PIP cycles. Fiber pull-out did not strongly occur at the fractured surface of the CMC (Fig. 4 (e–e’)). The roughness of the fiber surfaces increased after pyrolysis, which suppressed the pull-out of the fibers. During the 4-point bending test, the SiCfiber/SiCfiller/SiCmatrix CMC exhibited a brittle fracture behavior after reaching ultimate flexural strength (∼162 MPa) as shown in Fig. S4. As already seen from Fig. 4(e–e’), pulled out fibers were not frequently observed at the fractured surface of SiCfiber/SiCfiller/SiCmatrix CMC demonstrating strong interfacial bonding between the fibers and matrix owing to the lack of significant PyC interphase and the coarsening of SiC grains on the fiber surface [20]. XRD data of the CMC informed the formation of SiO2 phase after PIP, which was originated from the surface of oxidized SiC filler (Fig. S5). The mechanism of fiber damage by the SiO2 phase was described in detail in the Supplementary file. The formation of protective SiC coating on the surface of PyC-coated SiC fibers has been investigated in order to protect the fibers from the corrosive environment. Among the multi-layer coatings, SiC was a reaction barrier against corrosive reactants. The CMC showed two-fold bending strength and higher damage tolerance compared with the samples without the protective coatings. Researchers used SiC/PyC coatings and reported the protective effects of SiC coating against the reactive gases which was produced during the PIP process. The results indicated that the damage of the PyC coating which occurred in the present research may
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Fig. 2. Microscopic images of SiCf (a–a’) before and (b–b’) after sonication for 2 h. SEM images (c–c’) of SiC fibers after the PyC coating by CVI for 50 min at 1000 °C.
be minimized or suppressed by the application of SiC/PyC dual coating. Subsequent research is going on in order to clarify the protective effect of SiC/PyC dual coating against reaction (1) and (2) (Supplementary). The flexural strength of prepared SiCfiber/SiCfiller/SiCmatrix CMC was not high enough most probably because of the partial damage of PyC coating during the heat treatment from reactions (1) and (2) [20]. Also, the high pressure during CIP (50 MPa) could damage the fibers and reduce the strength. Additional experiments are going on in order to
find the proper CIP pressure to increase the green density while preventing the damage of the fibers. 4. Conclusion The novel intermediate steps including sonication, popping, electrophoretic deposition, vacuum infiltration and cold isostatic press (CIP) enhanced the infiltration of SiC matrix for the fabrication of SiCf/ 4
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Fig. 3. Loading of SiC powder (∼50 nm) on SiC fiber fabric with PyC coating thickness of 200 nm after EPD using different popping pressure (a). Loading of SiC powder (∼50 nm) on SiC fiber fabric with PyC coating thickness of 350 nm after EPD using different popping pressure (b) and the morphology of PyC coated SiC fibers after popping with different pressure: 0.6 MPa (c), 0.0 MPa (without popping) (d), 1.0 MPa (e).
SiC CMC. Among the tested intermediate steps, popping and CIP had a beneficial effect for increasing the green density and improving the homogeneous infiltration of the slurry into fiber fabrics. The optimum popping pressure increased with the increase of the PyC coating thickness. As high as 68 % of SiCfiber/SiCfiller green density was achieved by the optimization of the SiC slurry dispersion and slurry infiltration process into the fiber fabrics. The flexural strength of the CMC was 162 MPa after 7 PIP cycles and the CMC showed brittle fracture behavior. The PyC coating on the fibers was damaged after PIP process. The reaction of the PyC coating with SiO2 in the SiC filler was attributed to the main reason for the damage. CIP process may also induce the damage of the fibers.
Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We would like to acknowledge the financial support from the Korea Institute of Materials Science (Project No.: PNK-5620). The authors are thankful to the Director, CSIR-Advanced Materials and Processes Research Institute, Bhopal, for his support.
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Fig. 4. SEM images of SiCf/SiC after popping, EPD, Vacuum infiltration and CIP before PIP (a–b’, light green color), SEM images of polished SiCfiber/SiCfiller/SiCmatrix composite after seven cycles of PIP (c–d’, red color) at different resolutions. Morphology of the fractured surface of the CMC after bending test at room temperature (e–e’, blue color) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
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Appendix A. Supplementary data
(2013) 5623–5629. [10] B. Yang, X. Zhou, J. Yu, The properties of Cf/SiC composites prepared from different precursors, Ceram. Int. 41 (2015) 4207–4213. [11] Y. Mu, W. Zhou, H. Wang, C. Wang, Y. Qing, Mechanical and dielectric properties of 2.5D SiCf/SiC–Al2O3 composites prepared via precursor infiltration and pyrolysis, Mater. Sci. Eng. A 596 (2014) 64–70. [12] A. Iveković, G. Dražić, S. Novak, Densification of a SiC-matrix by electrophoretic deposition and polymer infiltration and pyrolysis process, J. Eur. Ceram. Soc. 31 (2011) 833–840. [13] K. Raju, H.-W. Yu, J.-Y. Park, D.-H. Yoon, Fabrication of SiCf/SiC composites by alternating current electrophoretic deposition (AC–EPD) and hot pressing, J. Eur. Ceram. Soc. 35 (2015) 503–511. [14] Y. Katoh, S.M. Dong, A. Kohyama, Thermo-mechanical properties and microstructure of silicon carbide composites fabricated by nano-infiltrated transient eutectoid process, Fusion Eng. Des. 61–62 (2002) 723–731. [15] C.A. Nannetti, A. Ortona, D.A. de Pinto, B. Riccardi, Manufacturing SiC-fiber-reinforced SiC matrix composites by improved CVI/slurry infiltration/polymer impregnation and pyrolysis, J. Am. Ceram. Soc. 87 (2004) 1205–1209. [16] Q. Li, S. Dong, P. He, H. Zhou, Z. Wang, J. Yang, B. Wu, J. Hu, Mechanical properties and microstructures of 2D Cf/ZrC–SiC composites using ZrC precursor and polycarbosilane, Ceram. Int. 38 (2012) 6041–6045. [17] B. Yoon, S.H. Lee, L. Feng, Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure, J. Am. Ceram. Soc. 101 (2018) 2760–2769. [18] J. Yin, S.-H. Lee, L. Feng, Y. Zhu, X. Liu, Z. Huang, S.-Y. Kim, I.-S. Han, The effects of SiC precursors on the microstructures and mechanical properties of SiCf/SiC composites prepared via polymer impregnation and pyrolysis process, Ceram. Int. 41 (2015) 4145–4153. [19] C. Yan, R. Liu, Y. Cao, C. Zhang, Fabrication and properties of PIP 3D Cf/ZrC–SiC composites, Mater. Sci. Eng. A 591 (2014) 105–110. [20] Y. Zhou, W. Zhou, F. Luo, D. Zhu, Effects of dip-coated BN interphase on mechanical properties of SiCf/SiC composites prepared by CVI process, Trans. Nonferrous Met. Soc. China 24 (2014) 1400–1406.
Supplementary material related to this article can be found, in the online version, at https://doi.org/10.1016/j.jeurceramsoc.2020.01. 009. References [1] J. Xin, S.H.I. Duoqi, Y. Xiaoguang, Z. Chaojun, Fiber strength measurement for KD-I (f)/SiC composites and correlation to tensile mechanical behavior at room and elevated temperatures, Ceram. Int. 41 (2015) 299–307. [2] X. Luo, P. Guo, Y. Yang, N. Jin, S. Liu, Z. Kou, S. Wu, Microstructure, tensile strength and thermostability of W-core SiC fibers with or without carbon coating, Mater. Sci. Eng. A 647 (2015) 265–276. [3] K.S. Lee, K.S. Jang, J.H. Park, T.W. Kim, I.S. Han, S.K. Woo, Designing the fiber volume ratio in SiC fiber-reinforced SiC ceramic composites under Hertzian stress, Mater. Des. 32 (2011) 4394–4401. [4] H. Yu, X. Zhou, W. Zhang, H. Peng, C. Zhang, Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases, Mater. Des. 44 (2013) 320–324. [5] J. Zhao, Y. Yu, B. Weng, W. Zhang, A.T. Harris, A.I. Minett, Z. Yue, X.-F. Huang, J. Chen, Sensitive and selective dopamine determination in human serum with inkjet printed Nafion/MWCNT chips, Electrochem. Commun. 37 (2013) 32–35. [6] G. Morscher, J. Cawley, Intermediate temperature strength degradationin SiC/SiC composites, J. Eur. Ceram. Soc. 22 (2002) 2777–2787. [7] H. Tian, H. Liu, H. Cheng, Mechanical and microwave dielectric properties of KD-I SiCf/SiC composites fabricated through precursor infiltration and pyrolysis, Ceram. Int. 40 (2014) 9009–9016. [8] M.A. Kmetz, K.C. Newton, Hybred polymer cvi composites, Google Patents, 2011. [9] J.-C. Bae, K.-Y. Cho, D.-H. Yoon, S.-S. Baek, J.-K. Park, J.-I. Kim, D.-W. Im, D.H. Riu, Highly efficient densification of carbon fiber-reinforced SiC-matrix composites by melting infiltration and pyrolysis using polycarbosilane, Ceram. Int. 39
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Contents lists available at ScienceDirect
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Short communication
Significance of modification of slurry infiltration process for the precursor impregnation and pyrolysis process of SiCf/SiC composites Shiv Singha,b,1,*, Jie Yinc,1, Lun Fengd, Dehi Pada Mondalb, Daejong Kime, Sea-Hoon Leea,** a
Division of Powder/Ceramics Research, Korea Institute of Materials Science, Changwon 641-831, Republic of Korea Lightweight Metallic Materials, Council of Scientific and Industrial Research-Advanced Materials and Processes Research Institute, Habibganj Naka, Hoshangabad Road, Bhopal, Madhya Pradesh 462026, India c State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 65049, China d Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO, USA e Nuclear Materials Development Division, Korea Atomic Energy Research Institute, Daejeon 305-353, Republic of Korea b
ARTICLE INFO
ABSTRACT
Keywords: Ceramic-matrix composites Infiltration Polymer precursor Silicon carbide Cold isostatic pressing
Several intermediate steps were applied before the precursor infiltration and pyrolysis process to improve the infiltration of SiC slurry for promoting the infiltration of SiC slurry into fiber voids. These steps include sonication, popping, electrophoretic deposition, vacuum infiltration and cold isostatic pressing (CIP). The intermediate processes, especially popping and CIP, had a beneficial effect on green density enhancement and improving the homogeneous infiltration of the slurry into fiber fabrics. The density of the SiCfiber/SiCfiller green body was 2.20 g/cm3, which corresponded to 68 % of relative density. The SiCf/SiC composite has a high density of 2.65 g/cm3 after seven PIP cycles.
1. Introduction Ceramic matrix composites (CMCs), particularly silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites, have been extensively used for high temperature and/or high-velocity environment including a nuclear reactor, rocket motor nozzles, aerospace applications, brake disk, semi-conductor industries, etc. [1–5]. SiCf/SiC composites possess superior characteristics over conventional metallic alloys and monolithic ceramics such as low density, thermodynamic stability, noteworthy creep/wear resistance, corrosion and oxidation resistance as well as excellent damage tolerance against adverse conditions [4,6,7]. There are numerous processes depending on the shape, size along with fabrication cost for developing SiC CMC composites. Chemical vapor infiltration (CVI), precursor infiltration and pyrolysis (PIP), liquid silicon infiltration, hot pressing and chemical liquid–vapor deposition are a few of them [7–9]. Among all routes, PIP is a relatively inexpensive process for the fabrication of multi-layered SiCf/SiC composites [7,9–11]. Nevertheless having aforesaid advantages, long processing time and large void spaces between fibers even after several PIP
cycles, along with the shrinkage cracking during pyrolysis are the main hurdles of this process [12]. In this context, several intermediate steps for promoting the infiltration of SiC slurry in between fibers have been incorporated before polymer infiltration in order to make composites of high green density and least porosity including low-pressure SiC slurry infiltration, ultra-sonication and electrophoretic deposition (EPD) [12–16]. In EPD, conscientious selection of SiC slurry concentration and optimized electric field provide a densely packed SiC green body which further help in the densification of SiCf/SiC composite [12]. In spite of the development of slurry infiltration processes described above, the nonhomogeneous infiltration of the slurry in between the fiber fabrics has been reported [12–16]. As a consequence, it is very important to understand the effects of each process and to develop alternative efficient processes. The purpose of current study is to investigate the effects of intermediate steps for promoting slurry infiltration in between fibers, such as the preparation of highly concentrated nano-SiC slurry, spreading and popping process of the woven fiber fabrics, EPD, vacuum/pressure infiltration along with cold isostatic pressing (CIP) processes, on the density, microstructure and mechanical strength of SiCf/SiC CMC
⁎ Corresponding author at: Lightweight Metallic Materials, Council of Scientific and Industrial Research-Advanced Materials and Processes Research Institute, Habibganj Naka, Hoshangabad Road, Bhopal, Madhya Pradesh 462026, India ⁎⁎ Corresponding author at: Division of Powder/Ceramics Research, Korea Institute of Materials Science, Changwon 641-831, Republic of Korea E-mail addresses: [email protected], [email protected] (S. Singh), [email protected] (S.-H. Lee). 1 Equal contribution.
https://doi.org/10.1016/j.jeurceramsoc.2020.01.009 Received 11 September 2019; Received in revised form 23 December 2019; Accepted 3 January 2020 0955-2219/ © 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: Shiv Singh, et al., Journal of the European Ceramic Society, https://doi.org/10.1016/j.jeurceramsoc.2020.01.009
Journal of the European Ceramic Society xxx (xxxx) xxx–xxx
S. Singh, et al.
fabricated via PIP process.
were prepared for reference purposes. All the processes were carried out for unpopped samples except popping.
2. Experimental details
2.3. Fabrication of SiCf/SiC composite via PIP and property analysis
2.1. Materials
A detailed description is given in supporting information. In brief, after completely drying the preform at 110 °C, the weight and volume of the SiCfiber/SiCfiller green body were measured in order to calculate the bulk density, and the samples were put inside the graphite molds. After pouring a significant amount of PCS and applying a vacuum for the infiltration of the liquid precursor into the green body, the samples were pressed by a tungsten plate (∼10 kg) using solid graphite punch [18]. Cross-linking was performed at 250 °C for 30 min and pyrolysis was done at 1400 °C for 2 h at a heating rate 5 °C and 1.5 °C, respectively. The whole analysis was accomplished in an argon atmosphere at atmospheric pressure. Seven cycles of PIP were executed to increase the density of SiCf/SiC composites.
Complete details are provided in the Supplementary information. 2.2. Pretreatment of SiC woven fabrics and slurry infiltration As received plane weaved SiC fiber fabrics were cut into 10 × 10 cm2 pieces and dipped into the de-ionized water. Ultra-sonication was performed for the expansion of plane-woven SiC fiber fabrics and consequent separation of individual fibers in the bundles using ultra sonicator (Sonics & Materials, USA) for 2 h. After drying at 105 °C for 12 h, pyrolytic carbon (PyC) coating (∼200 nm) was deposited by isothermal CVI at 1000 °C. The mixture of propane and hydrogen gas (molar ratio 6:1) was used as a carbon source and carrier gas, respectively for 50 min inside the reaction chamber. Next to CVI, PyC coated samples were cut into small pieces (3 × 3 cm2) for the novel popping process. The popping process was carried out in a thick wall stainless steel vessel with a variable air pressure of 0–1.0 MPa. After holding this pressure for 1 min, the lid of the vessel was opened forcefully for further expansion of SiC fibers using the rapid expansion of the gases in between the fibers. After this step, the optimization of the dispersion of SiC, prepared by high energy milling, was performed, which was described elsewhere in detail [17]. The dispersion of nano SiC (d50: 50 nm) (Fig. S1) was optimized as follows: 10 wt % of the nano SiC powder was dispersed with 10 wt% of different dispersants by ball milling at 200 r.p.m. (revolution per minute) for 12 h and subsequently by sonication for 30 min. Six dispersants (PEI-1000/5000/10000/300000, KV5068 and KV-9056) were tested with ethyl alcohol as the dispersoid. In some cases, ethyl alcohol was mixed with methyl ethyl ketone (MEK) (34:66 by weight ratio) in order to check the possibility of enhancing the dispersion behavior. The viscosity of 10 wt% slurry at 25 °C and the size distribution of the powder were determined using a viscometer (HB DV-II + pro, Brookfield Engineering Laboratories, MA, USA) and laser diffraction particle size analyzer (Coulter LS 13 320, Beckman Coulter Inc., Fl, USA), respectively. EPD was carried out for fifteen layers of fiber fabrics at an electrical field of 7.0 V for 10 min using 10 wt% nano SiC (d50: 50 nm) slurry. A probe sonicator was used in the whole process to improve the dispersion of SiC powder (VCX750, Sonics and Materials, CT, USA). A special type of EPD set-up was used where 7 SiC fabrics were separately put in one bath for EPD, i.e EPD was done individually for 15 fabrics. Vacuum/pressure infiltration was carried out using fifteen layers of processed SiC fabric. SiC powder with relatively large size (d50: 170 nm) prepared by the aforementioned mechanical alloying (MA) process was used to make 55 vol% slurry for infiltration. 1 wt% of PEI was used as a dispersant [17]. Multi-layered SiCf samples were put in a cylindrical vessel (chamber size = 4 × 4 × 1 cm3). Low pressure was created inside the chamber using a vacuum pump. Thereafter, a low vacuum chamber was filled with concentrated SiC slurry. Owing to low pressure, slurry penetrated very smoothly into a chamber and infiltrated in between SiC fiber fabrics. Subsequently, the chamber was pressurized with argon gas up to ∼0.15 MPa for enhancing the infiltration of SiC slurry. The pressure was released after 1 min. These vacuum and pressurization processes were repeated twice. Subsequent to this process, CIP was carried out for 15 min at 50 MPa pressure before the drying of the slurry. Subsequently, the samples were dried at 105 °C for 12 h. All the steps involved in the fabrication of composite are shown in Fig. 1. Some samples were also prepared using only sonication (expansion), popping, EPD or CIP in order to know the advantages of individual processes. However, vacuum infiltration was common for all the aforementioned samples. Also, unpopped samples
3. Results and discussion 3.1. Properties of SiC fiber fabrics The morphology of SiC fiber fabrics before and after sonication is displayed in Fig. 2. As-received SiC fabrics have significant void spaces in between the woven fiber bundles (Fig. 2a–a’). In contrast, the SiC fiber bundles which undergone ultra-sonication for 2 h were expanded in the fabrics significantly as shown in Fig. 2(b–b’). As a consequence, the voids in between the woven fiber bundles were filled. This expansion facilitates slurry infiltration in between fibers. Sonication was done before CVI to prevent possible damage to the PyC coating during sonication. PyC layer was deposited on the SiC fiber fabrics via isothermal CVI as shown in Fig. 2. PyC layer deposited on SiCf was smooth, uniform and continuous. The PyC coating partly closed the channels in between the fibers (Fig. 2(c)). Consequently, the slurry could not easily infiltrate into the pores in between the fibers. The thickness of PyC coating on the SiC fibers was 200 nm (Fig. 2 (c’)). 3.2. Densification of SiC fiber preform via slurry infiltration As shown in Fig. 3(a), primarily the loading of SiC filler increased up-to certain pressure (0.4 MPa) limit then it decreased with further pressure increase (Fig. S2). In order to understand the effect of PyC coating thickness on the optimum popping pressure, SiC fiber fabrics with a PyC coating thickness of 350 nm were prepared and tested (Fig. 3(b)). A similar mass change was observed with those shown in Fig. 3(a) except for the shift of optimum pressure from 0.4 MPa to 0.6 MPa, indicating that the optimum popping pressure increased with the increase of PyC coating thickness. The adjacent fibers are closely attached in unpopped samples (Fig. 3(d)). The popping process (0.6 MPa) separated the connected PyC coatings of the adjacent fibers (Fig. 3(c), and left marks on the surface of the coatings. The coatings began to be partially detached from the fiber surface. The separation of the PyC coating promoted the infiltration of the slurry into the pores between the fibers. However, when the popping pressure exceeded a certain value (1.0 MPa), the coating was mostly detached from the fiber surface in some areas (Fig. 3(e)). Because the electrical conduction of the SiC fiber was mainly performed by the PyC coating, the electrical conductivity of the fabrics decreased above the optimum popping pressure, which decreased the efficiency of the EPD process. Most of the pores of SiC fiber preform were filled with SiC filler during EPD process. Subsequent to EPD, vacuum/pressure infiltration was carried out using 55 vol% slurry for fifteen layers of the stacked fabrics in order to fill macropores between the fiber fabrics. The slurry infiltration technique was also responsible for reducing the number of PIP cycles because most of the macropores of the preform were partly filled before PIP. Vacuum infiltration of concentrated SiC slurry was performed to the 2
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Fig. 1. Schematic of steps involved in the fabrication SiCf/SiC composite.
stacked fabrics treated using different processes to understand the effects of each process on the infiltration of the SiC slurry (Fig. S3). These samples were tabulated in Table S1. In the expansion-CIP process condition, CIP of stacked fifteen layers of SiCf/SiC preform was performed under 50 MPa pressure immediately after vacuum/pressure infiltration, and before the increase of slurry viscosity by drying, in order to squeeze out extra SiC slurry from the fiber fabrics and further promoting the infiltration of the slurry. This process also facilitated in compact packing of SiCfiber/SiCfiller preform by applying high pressure to the preform, which reduced the thickness of prepared samples. Each process promoted the infiltration of the slurry. Especially, the beneficial effect of the popping and CIP process was clearly observed in Figs. S3(b) and (d), respectively. Fig. 4(a–b’) shows a cross-sectional micrograph of densified SiCfiber/ SiCfiller samples after the application of fiber expansion, popping, EPD and CIP at different resolutions before PIP. The void spaces in between the fibers/bundles are mostly filled by the aforementioned techniques used in the preparation of SiCfiber/SiCfiller samples. The SiC fillers, used during EPD and vacuum/pressure infiltration, were dispersed uniformly in the SiC fiber preform. The bulk density of prepared material was 2.20 g/cm3 after the drying of the sample, which corresponded to the relative density of 68 %. The micrographs of prepared polished SiCf/SiC CMCs are shown in Fig. 4(c–d’) after seven PIP cycles. The microstructures reveal that SiC matrices are uniformly and densely covered the empty spaces and pores in between the fibers. However, at some places, pores are observed owing to the incomplete filling of SiC filler during the slurry infiltration process. The free spaces in between the fibers and fibers bundles have been significantly filled by PCS after PIP, which is corroborated to high impregnation efficiency and relatively
small volume shrinkage occurred in the conversion of PCS [19]. The surface area of the CMC fabricated with and without popping was 13.91 and 14.19 m2/g and their porosity was 20.66 and 21.0 %, respectively. The SiCf/SiC CMC fabricated using the optimum conditions had a high density of 2.65 g/cm3 after seven PIP cycles. Fiber pull-out did not strongly occur at the fractured surface of the CMC (Fig. 4 (e–e’)). The roughness of the fiber surfaces increased after pyrolysis, which suppressed the pull-out of the fibers. During the 4-point bending test, the SiCfiber/SiCfiller/SiCmatrix CMC exhibited a brittle fracture behavior after reaching ultimate flexural strength (∼162 MPa) as shown in Fig. S4. As already seen from Fig. 4(e–e’), pulled out fibers were not frequently observed at the fractured surface of SiCfiber/SiCfiller/SiCmatrix CMC demonstrating strong interfacial bonding between the fibers and matrix owing to the lack of significant PyC interphase and the coarsening of SiC grains on the fiber surface [20]. XRD data of the CMC informed the formation of SiO2 phase after PIP, which was originated from the surface of oxidized SiC filler (Fig. S5). The mechanism of fiber damage by the SiO2 phase was described in detail in the Supplementary file. The formation of protective SiC coating on the surface of PyC-coated SiC fibers has been investigated in order to protect the fibers from the corrosive environment. Among the multi-layer coatings, SiC was a reaction barrier against corrosive reactants. The CMC showed two-fold bending strength and higher damage tolerance compared with the samples without the protective coatings. Researchers used SiC/PyC coatings and reported the protective effects of SiC coating against the reactive gases which was produced during the PIP process. The results indicated that the damage of the PyC coating which occurred in the present research may
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Fig. 2. Microscopic images of SiCf (a–a’) before and (b–b’) after sonication for 2 h. SEM images (c–c’) of SiC fibers after the PyC coating by CVI for 50 min at 1000 °C.
be minimized or suppressed by the application of SiC/PyC dual coating. Subsequent research is going on in order to clarify the protective effect of SiC/PyC dual coating against reaction (1) and (2) (Supplementary). The flexural strength of prepared SiCfiber/SiCfiller/SiCmatrix CMC was not high enough most probably because of the partial damage of PyC coating during the heat treatment from reactions (1) and (2) [20]. Also, the high pressure during CIP (50 MPa) could damage the fibers and reduce the strength. Additional experiments are going on in order to
find the proper CIP pressure to increase the green density while preventing the damage of the fibers. 4. Conclusion The novel intermediate steps including sonication, popping, electrophoretic deposition, vacuum infiltration and cold isostatic press (CIP) enhanced the infiltration of SiC matrix for the fabrication of SiCf/ 4
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Fig. 3. Loading of SiC powder (∼50 nm) on SiC fiber fabric with PyC coating thickness of 200 nm after EPD using different popping pressure (a). Loading of SiC powder (∼50 nm) on SiC fiber fabric with PyC coating thickness of 350 nm after EPD using different popping pressure (b) and the morphology of PyC coated SiC fibers after popping with different pressure: 0.6 MPa (c), 0.0 MPa (without popping) (d), 1.0 MPa (e).
SiC CMC. Among the tested intermediate steps, popping and CIP had a beneficial effect for increasing the green density and improving the homogeneous infiltration of the slurry into fiber fabrics. The optimum popping pressure increased with the increase of the PyC coating thickness. As high as 68 % of SiCfiber/SiCfiller green density was achieved by the optimization of the SiC slurry dispersion and slurry infiltration process into the fiber fabrics. The flexural strength of the CMC was 162 MPa after 7 PIP cycles and the CMC showed brittle fracture behavior. The PyC coating on the fibers was damaged after PIP process. The reaction of the PyC coating with SiO2 in the SiC filler was attributed to the main reason for the damage. CIP process may also induce the damage of the fibers.
Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We would like to acknowledge the financial support from the Korea Institute of Materials Science (Project No.: PNK-5620). The authors are thankful to the Director, CSIR-Advanced Materials and Processes Research Institute, Bhopal, for his support.
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Fig. 4. SEM images of SiCf/SiC after popping, EPD, Vacuum infiltration and CIP before PIP (a–b’, light green color), SEM images of polished SiCfiber/SiCfiller/SiCmatrix composite after seven cycles of PIP (c–d’, red color) at different resolutions. Morphology of the fractured surface of the CMC after bending test at room temperature (e–e’, blue color) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
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Appendix A. Supplementary data
(2013) 5623–5629. [10] B. Yang, X. Zhou, J. Yu, The properties of Cf/SiC composites prepared from different precursors, Ceram. Int. 41 (2015) 4207–4213. [11] Y. Mu, W. Zhou, H. Wang, C. Wang, Y. Qing, Mechanical and dielectric properties of 2.5D SiCf/SiC–Al2O3 composites prepared via precursor infiltration and pyrolysis, Mater. Sci. Eng. A 596 (2014) 64–70. [12] A. Iveković, G. Dražić, S. Novak, Densification of a SiC-matrix by electrophoretic deposition and polymer infiltration and pyrolysis process, J. Eur. Ceram. Soc. 31 (2011) 833–840. [13] K. Raju, H.-W. Yu, J.-Y. Park, D.-H. Yoon, Fabrication of SiCf/SiC composites by alternating current electrophoretic deposition (AC–EPD) and hot pressing, J. Eur. Ceram. Soc. 35 (2015) 503–511. [14] Y. Katoh, S.M. Dong, A. Kohyama, Thermo-mechanical properties and microstructure of silicon carbide composites fabricated by nano-infiltrated transient eutectoid process, Fusion Eng. Des. 61–62 (2002) 723–731. [15] C.A. Nannetti, A. Ortona, D.A. de Pinto, B. Riccardi, Manufacturing SiC-fiber-reinforced SiC matrix composites by improved CVI/slurry infiltration/polymer impregnation and pyrolysis, J. Am. Ceram. Soc. 87 (2004) 1205–1209. [16] Q. Li, S. Dong, P. He, H. Zhou, Z. Wang, J. Yang, B. Wu, J. Hu, Mechanical properties and microstructures of 2D Cf/ZrC–SiC composites using ZrC precursor and polycarbosilane, Ceram. Int. 38 (2012) 6041–6045. [17] B. Yoon, S.H. Lee, L. Feng, Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure, J. Am. Ceram. Soc. 101 (2018) 2760–2769. [18] J. Yin, S.-H. Lee, L. Feng, Y. Zhu, X. Liu, Z. Huang, S.-Y. Kim, I.-S. Han, The effects of SiC precursors on the microstructures and mechanical properties of SiCf/SiC composites prepared via polymer impregnation and pyrolysis process, Ceram. Int. 41 (2015) 4145–4153. [19] C. Yan, R. Liu, Y. Cao, C. Zhang, Fabrication and properties of PIP 3D Cf/ZrC–SiC composites, Mater. Sci. Eng. A 591 (2014) 105–110. [20] Y. Zhou, W. Zhou, F. Luo, D. Zhu, Effects of dip-coated BN interphase on mechanical properties of SiCf/SiC composites prepared by CVI process, Trans. Nonferrous Met. Soc. China 24 (2014) 1400–1406.
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