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Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction
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FUSION-8436; No. of Pages 5
Fusion Engineering and Design xxx (2015) xxx–xxx
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Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction Joon-Soo Park a,∗ , Hiroshi Nishimura b , Daisuke Hayasaka a,b , Ju-Hyeon Yu b , Hirotatsu Kishimoto a , Akira Kohyama a a b
OASIS, Muroran Institute of Technology, Muroran 050-8585, Japan Graduated School of Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan
a r t i c l e
i n f o
Article history: Received 5 September 2015 Received in revised form 16 December 2015 Accepted 23 December 2015 Available online xxx Keywords: NITE process SiC/SiC composites Short fiber
a b s t r a c t Short fiber reinforced SiC/SiC composites with high fiber volume fraction were fabricated by NITE process. The effects of fiber length and sintering condition on microstructure and mechanical properties were investigated. Although, high sintering temperature promotes the densification of SiC matrix but leads to the degradation of F/M interface. The flexural strength of SF-SiC/SiC with long fiber length shows higher flexural strength compared to those of SF-SiC/SiC with short fiber length. SF-SiC/SiC composites with complicated shape have been successfully fabricated by pseudo-HIP. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Continuous SiC fiber reinforced SiC matrix (SiC/SiC) composites are one of promising structural materials for nuclear energy and aerospace application due to their excellent properties such as light weight, high strength, reliability under high temperature, low after heat, low radioactivity and so on [1]. In recent, it is encouraged to use SiC/SiC components by the commercialization of high crystalline and high purity SiC fibers as well as the development of their innovative fabrication process, like Nano Infiltration and Transient Eutectic (NITE) process [2–4]. NITE-SiC/SiC composites are consisted of well densified SiC matrix and well aligned continuous SiC fiber with thin pyrocarbon (PyC) coating as fiber/matrix (F/M) interface. Due to its dens microstructure and high mechanical properties, it is considered as one of nuclear grade SiC/SiC composites [5]. In the other hand, we must carefully discuss on the anisotropic properties of SiC/SiC composites for their practical use. Because, the thermo-mechanical properties of continuous fiber reinforced composites strongly depend on fiber reinforcing architecture. In
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (J.-S. Park).
case of fusion reactor environments, thermal gradient inside the material occurred by a high heat flux. This thermal gradient gives differential swelling under irradiation, as well as differential thermal expansion, resulting in the complicated stress field inside the material [6,7]. Thus, the evaluation of off-axial mechanical properties of SiC/SiC composites is one of the important technical issues for fusion application. Actually, it is well known that the specimen with unidirectional fiber (UD) reinforcing architecture shows quite low strength in non-fiber direction. In the other hand, short fiber reinforced composites, there is no need to consider about the anisotropy due to their randomly aligned fiber architecture. Moreover, it provides many advantages, such as high productivity of practical components with large sizes and complicated shapes, shorter process time and lower cost. Although, there are many advantages of short fiber as mentioned above, but only limited data concerned on short fiber (SF) SiC/SiC composites have been reported [8]. The production of homogeneous SF-SiC/SiC composites with high fiber volume fraction (Vf ) is quite difficult, because of the entanglement of short fibers. As a result, Vf of SF-SiC or C/SiC was usually under 40% and it may be difficult to obtain sufficient effects of fiber reinforcing [8–10]. The purpose of this work is the process development of high Vf SF-SiC/SiC composites based on NITE process. The effects of fiber length and sintering conditions on the microstructure and
http://dx.doi.org/10.1016/j.fusengdes.2015.12.060 0920-3796/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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Fig. 2. Conceptual diagram of fabrication process for near net shaped SF-SiC/SiC by P-HIP.
Fig. 1. Fabrication process of SF-SiC/SiC composites.
mechanical properties of SF-SiC/SiC were investigated. Near net shaping of SF-SiC/SiC composites with complicated shape was also performed by pseudo-hot isostatic press (P-HIP) method. 2. Experimental procedures Highly crystallized SiC fiber, Cef-NITETM (GUNZE LIMITED, Japan), has been used as a reinforcing fiber. Fiber diameter is approximately 10 m. Number of fiber filaments per bundle is 800. As F/M interface, thin PyC coat (thickness < 500 nm) has been formed on fiber surface by conventional chemical vapor deposition (CVD) method. SiC powder, small amount of oxide additives and SiC based polymer binder were used as raw materials for SiC matrix. In this study, cut prepreg sheet has been used for the intermediate materials for SF-SiC/SiC. Prepreg sheets consisted of uni-directionally aligned continuous fiber bundles impregnating with SiC matrix precursor (SiC powder, additives and binder). It has the controlled weight ratio of fiber and matrix in order to obtain SF-SiC/SiC with high Vf (approx. 45 vol%). The thickness and bulk density of prepreg sheets are about 0.35 mm and 1.6 g/cm3 respectively. Short fiber including SiC matrix precursor was prepared by cutting of narrow prepreg sheet (width 2–3 mm). In order to investigate the effects of fiber length, cut prepreg sheet with different lengths (5 mm and 10 mm) were prepared. And then, 20 g of cut prepreg sheets was filled into the carbon mold for hot pressing (HP). Dimension of carbon mold is 40 mm × 40 mm. The condition of HP temperatures are 1820, 1830 and 1840 ◦ C. Maximum pressure, holding time and atmospheric condition are 20 MPa, 1.5 h and vacuum, respectively. The flow of fabrication process and the key conditions of SF-SiC/SiC composites are shown in Fig. 1 and Table 1.
Bar type specimens with dimensions of 3 mmw × 26 mmL × 1.2 mmt were machined, from the sintered body. 5 samples per each specimen were prepared to obtain average value. All samples in the same specimen were cut with the same direction. The effect of cutting direction was ignored in this study. Flexural strength was measured by the three point bending test using UTM. (Type 205R, INTESCO Co., Ltd., Japan.) The span of support pins and test speed are 16 mm and 0.5 mm/min, respectively. After bending test, the fracture surfaces of tested specimens were observed by FE-SEM (JEOL, JSM-6700F, Japan). In order to investigate the feasibility of near net shaping of SFSiC/SiC composites, SF-SiC/SiC with dome shape with dimensions of outer diameter ∅ 40 mm × inner diameter ∅ 38 mm × length 50 mm has been fabricated. Conceptual diagram of its fabrication process is shown in Fig. 2. Preform was prepared using short fibers (length 10 mm) and metallic dies with groove. It is essential to add isostatic pressure for the homogeneous densification of preform with complicated shapes. Thus, P-HIP has been selected as sintering method. Although inert gas in HIP is usually used as pressure transmitter, carbon powder is used in P-HIP [4,11]. During hot press, unidirectional load is transmitted to the pseudo isostatic pressure by carbon powder.
3. Experimental results and discussions Fig. 3 shows the appearance of SF2 specimens as an example of SF-SiC/SiC composites fabricated in this work. The unique architecture of randomly aligned short fibers, which are prepared by cutting of prepreg sheet, can be confirmed from the naked eye observation of plate surface.
Table 1 Fabrication conditions of SF-SiC/SiC specimen. ID
Sintering temperature [ ◦ C]
SF1 SF2 SF3 SF4 SF5a
1820 1830
a
1840
Repeat of SF4.
Fiber length [mm] 5 5 10 5 5
Density [g/cm3 ]
Flexural strength [MPa]
2.82 2.76 2.87 2.88 2.94
100 96 135 99 100
Fig. 3. Appearance of NITE-SiC/SiC composites prepared with short fibers (fiber length: 5 mm).
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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Fig. 4. Effects of sintering temperature on the flexural strength and density of SFSiC/SiC.
3.1. Effects of sintering temperature Fig. 4 shows the effects of sintering temperature on the flexural strength and density of SF-SiC/SiC composites. There is little difference in the flexural strength of each specimen. The flexural strengths of SF-SiC/SiC composites were about 100 MPa. The specimens sintered at 1840 ◦ C show relatively high density (2.94 g/cm3 ) compared with the others. Fig. 5 shows the fracture surface observation results after the flexural test. Every specimen shows complicated crack branching and deflection, which is one of general toughening mechanisms in CMCs (Ceramic Matrix Composites). From the specimens sintered at lower temperature, macro pores are usually found at inter fiber bundles. It was estimated that the interference between SiC fiber bundles suppressed the pressure transition required for the densification of SiC matrix and it is one of main reason of the remaining
3
Fig. 6. Effects of fiber length on the flexural strength and density of SF-SiC/SiC.
of inter bundle macro pore and large variation of strength data in SF1. On the other hand, highly densified SiC matrix including small amount of intra-bundle micro pores can be observed at the microstructure of SF4 and SF5. But, the significant loss of F/M interface is also observed at the microstructure of SF5. These results indicate that higher sintering temperature promotes the SiC matrix densification, but it leads to the degradation of PyC interphase. 3.2. Effects of fiber length The specimens with different fiber length have been prepared to investigate the effects of fiber length. In order to avoid the loss of F/M interface and fiber damage, specimens were sintered at 1830 ◦ C. Fig. 6 shows the effects of fiber length on the flexural strength and density of SF-SiC/SiC.
Fig. 5. FE-SEM observation results of SF-SiC/SiC composites sintered at different temperatures.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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Fig. 7. FE-SEM observation results of SF-SiC/SiC composites with different fiber length.
Flexural strength of SF2 and SF3 are 96 MPa and 135 MPa, respectively. The strength and density of SF3 with long fiber length shows slightly higher than those of SF2. However, the strength of SF3 is still lower than that of NITE-SiC/SiC composites reinforced by long continuous fiber. The flexural strength of unidirectional (UD) and cross-ply (0/90) NITE-SiC/SiC composites are <500 MPa and <200 MPa, respectively [12,13]. Fig. 7 shows the results of FE-SEM observation. Inter bundle macro pores are also found from the microstructure of SF3. In usual, longer reinforcing fiber leads to more complicated and long crack deflection, which make it possible to improve the mechanical properties. But, clear difference was not found from the microstructural observation. Further investigation is required to clear the effects of fiber length on the fracture manner of SF-SiC/SiC. 3.3. Near net shaping of SF-SiC/SiC SF-SiC/SiC with dome shape has been sintered by P-HIP. Fig. 8 shows the appearance of specimen after P-HIP and the results of fracture surface observation. It was confirmed that SF-SiC/SiC sintered by P-HIP has sound F/M interface as well as highly densified SiC matrix. Because of random fiber alignment, high Vf and sound F/M interface, it shows very rough and complicated fracture surface. But, further study is needed to quantification of its mechanical properties including strength and fracture resistance. 4. Summary Based on NITE process, the fabrication method for SF-SiC/SiC composites with high Vf has been discussed in this study. We have succeeded in fabricating of SF-SiC/SiC composites with High Vf (approx. 45 vol%) by using of cut prepreg sheets. It was revealed that high sintering temperature promotes the densification of SiC matrix but leads to the degradation of F/M interface. SF-SiC/SiC
Fig. 8. Appearance and FE-SEM observation results of SF-SiC/SiC composites sintered by P-HIP.
composites with long fiber length shows higher flexural strength (135 MPa) than those of shorter one. It was also shown that SFSiC/SiC with complicated shape can be obtained by using P-HIP. Further study is still needed to optimize the process condition of SF-SiC/SiC and to clarify/quantify their mechanical properties. References [1] A. Kohyama, M. Singh, H.T. Lin, Y. Katoh (Eds.), Advanced SiC/SiC Ceramic Composites Ceramics Transactions, vol. 144, American Ceramic Society, 2002. [2] Y. Katoh, et al., Thermo-mechanical properties and microstructure of silicon carbide composites fabricated by nano-infiltrated transient eutectoid process, Fusion Eng. Des. 61–62 (2002) 723–731. [3] A. Kohyama, et al., Advanced SiC fibers and SiC/SiC composites toward industrialization, J. Nuclear Mater. 417 (1–3) (2011) 340–343. [4] J.S. Park, et al., Efforts on large scale production of NITE-SiC/SiC composites, J. Nuclear Eng. 367–370 (A) (2007) 719–724. [5] T. Hinoki, et al., Silicon carbide and silicon carbide composites for fusion reactor application, Mater. Trans. 54 (4) (2013) 472–476. [6] T. Nozawa, et al., Determination and prediction of axial/off-axial mechanical properties of SiC/SiC composites, Fusion Eng. Des. 87 (5–6) (2012) 803–807. [7] Final Report for “procurement arrangement for the R&D on SiC/SiC composite in phase 2-2 for the DEMO R&D for the IFERC Project”, IFERC-T1PA03-JA-Del-1.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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[8] J.S. Lee, et al., Fabrication of short-fiber-reinforced SiC composites by polycarbosilane infiltration, J. Eur. Ceram. Soc. 24 (2004) 25–31. [9] W.S. Yang, et al., Microstructure and mechanical properties of milled fibre/SiC multilayer composites prepared by tape casting and pressureless sintering, Mater. Sci. Eng. A588 (2013) 103–110. [10] H. Tang, et al., Mechanical and tribological properties of short-fiber-reinforced SiC composites, Tribol. Int. 42 (2009) 823–827.
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[11] M. Suzuki, et al., Preparation and properties of dense SiC/SiC composites, Ceram. Eng. Sci. Proc. 26 (2) (2008) 319–326. [12] N. Nakazato, et al., Effects of pressure during preform densification on SiC/SiC composites, Open J. Inorg. Non-met. Mater. 3 (2013) 10–13. [13] N. Nakazato, et al., Effects of preform densification on microstructure and mechanical properties of SiC/SiC composites, Nippon Kinzoku Gakkaishi/J. Jpn. Inst. Met. 75 (3) (2011) 146–151.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
ARTICLE IN PRESS
FUSION-8436; No. of Pages 5
Fusion Engineering and Design xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction Joon-Soo Park a,∗ , Hiroshi Nishimura b , Daisuke Hayasaka a,b , Ju-Hyeon Yu b , Hirotatsu Kishimoto a , Akira Kohyama a a b
OASIS, Muroran Institute of Technology, Muroran 050-8585, Japan Graduated School of Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan
a r t i c l e
i n f o
Article history: Received 5 September 2015 Received in revised form 16 December 2015 Accepted 23 December 2015 Available online xxx Keywords: NITE process SiC/SiC composites Short fiber
a b s t r a c t Short fiber reinforced SiC/SiC composites with high fiber volume fraction were fabricated by NITE process. The effects of fiber length and sintering condition on microstructure and mechanical properties were investigated. Although, high sintering temperature promotes the densification of SiC matrix but leads to the degradation of F/M interface. The flexural strength of SF-SiC/SiC with long fiber length shows higher flexural strength compared to those of SF-SiC/SiC with short fiber length. SF-SiC/SiC composites with complicated shape have been successfully fabricated by pseudo-HIP. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Continuous SiC fiber reinforced SiC matrix (SiC/SiC) composites are one of promising structural materials for nuclear energy and aerospace application due to their excellent properties such as light weight, high strength, reliability under high temperature, low after heat, low radioactivity and so on [1]. In recent, it is encouraged to use SiC/SiC components by the commercialization of high crystalline and high purity SiC fibers as well as the development of their innovative fabrication process, like Nano Infiltration and Transient Eutectic (NITE) process [2–4]. NITE-SiC/SiC composites are consisted of well densified SiC matrix and well aligned continuous SiC fiber with thin pyrocarbon (PyC) coating as fiber/matrix (F/M) interface. Due to its dens microstructure and high mechanical properties, it is considered as one of nuclear grade SiC/SiC composites [5]. In the other hand, we must carefully discuss on the anisotropic properties of SiC/SiC composites for their practical use. Because, the thermo-mechanical properties of continuous fiber reinforced composites strongly depend on fiber reinforcing architecture. In
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (J.-S. Park).
case of fusion reactor environments, thermal gradient inside the material occurred by a high heat flux. This thermal gradient gives differential swelling under irradiation, as well as differential thermal expansion, resulting in the complicated stress field inside the material [6,7]. Thus, the evaluation of off-axial mechanical properties of SiC/SiC composites is one of the important technical issues for fusion application. Actually, it is well known that the specimen with unidirectional fiber (UD) reinforcing architecture shows quite low strength in non-fiber direction. In the other hand, short fiber reinforced composites, there is no need to consider about the anisotropy due to their randomly aligned fiber architecture. Moreover, it provides many advantages, such as high productivity of practical components with large sizes and complicated shapes, shorter process time and lower cost. Although, there are many advantages of short fiber as mentioned above, but only limited data concerned on short fiber (SF) SiC/SiC composites have been reported [8]. The production of homogeneous SF-SiC/SiC composites with high fiber volume fraction (Vf ) is quite difficult, because of the entanglement of short fibers. As a result, Vf of SF-SiC or C/SiC was usually under 40% and it may be difficult to obtain sufficient effects of fiber reinforcing [8–10]. The purpose of this work is the process development of high Vf SF-SiC/SiC composites based on NITE process. The effects of fiber length and sintering conditions on the microstructure and
http://dx.doi.org/10.1016/j.fusengdes.2015.12.060 0920-3796/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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Fig. 2. Conceptual diagram of fabrication process for near net shaped SF-SiC/SiC by P-HIP.
Fig. 1. Fabrication process of SF-SiC/SiC composites.
mechanical properties of SF-SiC/SiC were investigated. Near net shaping of SF-SiC/SiC composites with complicated shape was also performed by pseudo-hot isostatic press (P-HIP) method. 2. Experimental procedures Highly crystallized SiC fiber, Cef-NITETM (GUNZE LIMITED, Japan), has been used as a reinforcing fiber. Fiber diameter is approximately 10 m. Number of fiber filaments per bundle is 800. As F/M interface, thin PyC coat (thickness < 500 nm) has been formed on fiber surface by conventional chemical vapor deposition (CVD) method. SiC powder, small amount of oxide additives and SiC based polymer binder were used as raw materials for SiC matrix. In this study, cut prepreg sheet has been used for the intermediate materials for SF-SiC/SiC. Prepreg sheets consisted of uni-directionally aligned continuous fiber bundles impregnating with SiC matrix precursor (SiC powder, additives and binder). It has the controlled weight ratio of fiber and matrix in order to obtain SF-SiC/SiC with high Vf (approx. 45 vol%). The thickness and bulk density of prepreg sheets are about 0.35 mm and 1.6 g/cm3 respectively. Short fiber including SiC matrix precursor was prepared by cutting of narrow prepreg sheet (width 2–3 mm). In order to investigate the effects of fiber length, cut prepreg sheet with different lengths (5 mm and 10 mm) were prepared. And then, 20 g of cut prepreg sheets was filled into the carbon mold for hot pressing (HP). Dimension of carbon mold is 40 mm × 40 mm. The condition of HP temperatures are 1820, 1830 and 1840 ◦ C. Maximum pressure, holding time and atmospheric condition are 20 MPa, 1.5 h and vacuum, respectively. The flow of fabrication process and the key conditions of SF-SiC/SiC composites are shown in Fig. 1 and Table 1.
Bar type specimens with dimensions of 3 mmw × 26 mmL × 1.2 mmt were machined, from the sintered body. 5 samples per each specimen were prepared to obtain average value. All samples in the same specimen were cut with the same direction. The effect of cutting direction was ignored in this study. Flexural strength was measured by the three point bending test using UTM. (Type 205R, INTESCO Co., Ltd., Japan.) The span of support pins and test speed are 16 mm and 0.5 mm/min, respectively. After bending test, the fracture surfaces of tested specimens were observed by FE-SEM (JEOL, JSM-6700F, Japan). In order to investigate the feasibility of near net shaping of SFSiC/SiC composites, SF-SiC/SiC with dome shape with dimensions of outer diameter ∅ 40 mm × inner diameter ∅ 38 mm × length 50 mm has been fabricated. Conceptual diagram of its fabrication process is shown in Fig. 2. Preform was prepared using short fibers (length 10 mm) and metallic dies with groove. It is essential to add isostatic pressure for the homogeneous densification of preform with complicated shapes. Thus, P-HIP has been selected as sintering method. Although inert gas in HIP is usually used as pressure transmitter, carbon powder is used in P-HIP [4,11]. During hot press, unidirectional load is transmitted to the pseudo isostatic pressure by carbon powder.
3. Experimental results and discussions Fig. 3 shows the appearance of SF2 specimens as an example of SF-SiC/SiC composites fabricated in this work. The unique architecture of randomly aligned short fibers, which are prepared by cutting of prepreg sheet, can be confirmed from the naked eye observation of plate surface.
Table 1 Fabrication conditions of SF-SiC/SiC specimen. ID
Sintering temperature [ ◦ C]
SF1 SF2 SF3 SF4 SF5a
1820 1830
a
1840
Repeat of SF4.
Fiber length [mm] 5 5 10 5 5
Density [g/cm3 ]
Flexural strength [MPa]
2.82 2.76 2.87 2.88 2.94
100 96 135 99 100
Fig. 3. Appearance of NITE-SiC/SiC composites prepared with short fibers (fiber length: 5 mm).
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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FUSION-8436; No. of Pages 5
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Fig. 4. Effects of sintering temperature on the flexural strength and density of SFSiC/SiC.
3.1. Effects of sintering temperature Fig. 4 shows the effects of sintering temperature on the flexural strength and density of SF-SiC/SiC composites. There is little difference in the flexural strength of each specimen. The flexural strengths of SF-SiC/SiC composites were about 100 MPa. The specimens sintered at 1840 ◦ C show relatively high density (2.94 g/cm3 ) compared with the others. Fig. 5 shows the fracture surface observation results after the flexural test. Every specimen shows complicated crack branching and deflection, which is one of general toughening mechanisms in CMCs (Ceramic Matrix Composites). From the specimens sintered at lower temperature, macro pores are usually found at inter fiber bundles. It was estimated that the interference between SiC fiber bundles suppressed the pressure transition required for the densification of SiC matrix and it is one of main reason of the remaining
3
Fig. 6. Effects of fiber length on the flexural strength and density of SF-SiC/SiC.
of inter bundle macro pore and large variation of strength data in SF1. On the other hand, highly densified SiC matrix including small amount of intra-bundle micro pores can be observed at the microstructure of SF4 and SF5. But, the significant loss of F/M interface is also observed at the microstructure of SF5. These results indicate that higher sintering temperature promotes the SiC matrix densification, but it leads to the degradation of PyC interphase. 3.2. Effects of fiber length The specimens with different fiber length have been prepared to investigate the effects of fiber length. In order to avoid the loss of F/M interface and fiber damage, specimens were sintered at 1830 ◦ C. Fig. 6 shows the effects of fiber length on the flexural strength and density of SF-SiC/SiC.
Fig. 5. FE-SEM observation results of SF-SiC/SiC composites sintered at different temperatures.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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Fig. 7. FE-SEM observation results of SF-SiC/SiC composites with different fiber length.
Flexural strength of SF2 and SF3 are 96 MPa and 135 MPa, respectively. The strength and density of SF3 with long fiber length shows slightly higher than those of SF2. However, the strength of SF3 is still lower than that of NITE-SiC/SiC composites reinforced by long continuous fiber. The flexural strength of unidirectional (UD) and cross-ply (0/90) NITE-SiC/SiC composites are <500 MPa and <200 MPa, respectively [12,13]. Fig. 7 shows the results of FE-SEM observation. Inter bundle macro pores are also found from the microstructure of SF3. In usual, longer reinforcing fiber leads to more complicated and long crack deflection, which make it possible to improve the mechanical properties. But, clear difference was not found from the microstructural observation. Further investigation is required to clear the effects of fiber length on the fracture manner of SF-SiC/SiC. 3.3. Near net shaping of SF-SiC/SiC SF-SiC/SiC with dome shape has been sintered by P-HIP. Fig. 8 shows the appearance of specimen after P-HIP and the results of fracture surface observation. It was confirmed that SF-SiC/SiC sintered by P-HIP has sound F/M interface as well as highly densified SiC matrix. Because of random fiber alignment, high Vf and sound F/M interface, it shows very rough and complicated fracture surface. But, further study is needed to quantification of its mechanical properties including strength and fracture resistance. 4. Summary Based on NITE process, the fabrication method for SF-SiC/SiC composites with high Vf has been discussed in this study. We have succeeded in fabricating of SF-SiC/SiC composites with High Vf (approx. 45 vol%) by using of cut prepreg sheets. It was revealed that high sintering temperature promotes the densification of SiC matrix but leads to the degradation of F/M interface. SF-SiC/SiC
Fig. 8. Appearance and FE-SEM observation results of SF-SiC/SiC composites sintered by P-HIP.
composites with long fiber length shows higher flexural strength (135 MPa) than those of shorter one. It was also shown that SFSiC/SiC with complicated shape can be obtained by using P-HIP. Further study is still needed to optimize the process condition of SF-SiC/SiC and to clarify/quantify their mechanical properties. References [1] A. Kohyama, M. Singh, H.T. Lin, Y. Katoh (Eds.), Advanced SiC/SiC Ceramic Composites Ceramics Transactions, vol. 144, American Ceramic Society, 2002. [2] Y. Katoh, et al., Thermo-mechanical properties and microstructure of silicon carbide composites fabricated by nano-infiltrated transient eutectoid process, Fusion Eng. Des. 61–62 (2002) 723–731. [3] A. Kohyama, et al., Advanced SiC fibers and SiC/SiC composites toward industrialization, J. Nuclear Mater. 417 (1–3) (2011) 340–343. [4] J.S. Park, et al., Efforts on large scale production of NITE-SiC/SiC composites, J. Nuclear Eng. 367–370 (A) (2007) 719–724. [5] T. Hinoki, et al., Silicon carbide and silicon carbide composites for fusion reactor application, Mater. Trans. 54 (4) (2013) 472–476. [6] T. Nozawa, et al., Determination and prediction of axial/off-axial mechanical properties of SiC/SiC composites, Fusion Eng. Des. 87 (5–6) (2012) 803–807. [7] Final Report for “procurement arrangement for the R&D on SiC/SiC composite in phase 2-2 for the DEMO R&D for the IFERC Project”, IFERC-T1PA03-JA-Del-1.
Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060
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ARTICLE IN PRESS J.-S. Park et al. / Fusion Engineering and Design xxx (2015) xxx–xxx
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Please cite this article in press as: J.-S. Park, et al., Fabrication of short SiC fiber reinforced SiC matrix composites with high fiber volume fraction, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.060