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Preparation of a nanostructured SiC-ZrO2 coating to improve the oxidation resistance of graphite
SCT-21545; No of Pages 7 Surface & Coatings Technology xxx (2016) xxx–xxx
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Preparation of a nanostructured SiC-ZrO2 coating to improve the oxidation resistance of graphite Jalil Pourasad ⁎, Naser Ehsani, Zia Valefi, Sayed Ali Khalifesoltani Faculty of Materials and Manufacturing Technology, Malek-Ashtar University of Technology, Tehran, Iran
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Article history: Received 16 June 2016 Revised 22 August 2016 Accepted in revised form 31 August 2016 Available online xxxx Keywords: Graphite Oxidation resistance Nanostructure SiC ZrO2 Pack cementation
a b s t r a c t A nanostructured SiC/SiC-ZrO2 coating was prepared on a graphite substrate by a two-step technique to improve the oxidation protection ability of graphite. The first step was to prepare a functionally graded SiC layer by a pack cementation process and the second one was to obtain a SiC-ZrO2 coating through a pack cementation technique at 1873 K. The phase compositions and microstructure of the coating were characterized by X-ray diffraction and scanning electron microscopy. The isothermal oxidation test of the coated samples was performed at 1773 K for 10 h. A gradient C–SiC transition layer can be observed at the graphite-coating interface and a SiC-ZrO2 coating was formed. The SiC nanofibers with the diameter in the range of 30–160 nm were observed on the coating. The SiC-ZrO2 coating could efficiently improve oxidation resistance of graphite with a weight loss of 11%, as compared with a 70% weight loss of the first step coating. © 2016 Published by Elsevier B.V.
1. Introduction Carbon/carbon materials and graphite were known to be widely used for high temperature structural applications such as aero engine and turbine components due to the maintenance of their mechanical and thermal properties. However, the oxidation of carbon-based materials above 773 K in air cannot meet the request of practical application requirement, specifically for high-temperature causing a fall in their mechanical properties. Certainly, with the increase in oxidation temperature, the rate of graphite chemical reaction with oxygen, as well as the extent of oxidation, is extremely increased. Therefore, more studies have been conducted in an attempt to protect graphite against oxidation [1–3]. It is well known that the SiC coating is an effective method for protecting graphite at high temperature, since it can significantly avoid the oxygen diffusion into the graphite by producing a protective layer. In addition, the glass SiO2 film will be formed on the surface of the coating while the SiC coated graphite is placed in air at high temperature, which can efficiently inhibit oxygen from diffusing into the graphite. However, the mismatch of the thermal expansion coefficient between graphite and the SiC coating commonly lead to cracking of SiC coating, facilitating the oxygen diffusion to graphite substrate and the failure of the coating. Therefore, the protective temperature range of SiC coating is narrow, which limits the coating application for protection of graphite against oxidation [4–8]. ZrB2–SiC ceramic coating is a promising solution to improve ablation property of the graphite. The ⁎ Corresponding author. E-mail address: [email protected] (J. Pourasad).
ZrO2 produced by oxidation of ZrB2 can react with SiO2 to form ZrSiO4, which is beneficial to oxidation resistance ability due to its low permeability for oxygen and high thermal stability at high temperature. The high-thermally stable ZrSiO4 can be expected to reduce the consumption of SiO2 and improve the oxidation resistance of SiC coating at high temperature [9–11]. Wang et al. [12] used a two-step pack cementation method with ZrB2, Si and graphite powders at 2273 K to prepare ZrB2–SiC coating on graphite, which showed (ZrB2–SiC)/SiC coatings can better protect the graphite matrix than SiC coating from oxidation. Ren et al. [13] prepared a ZrB2–SiC gradient coating by a pack cementation process with Si, ZrO2, B2O3 and graphite powders at 2373 K. The effective self-sealing property of the protective silicate glass layer as well as the pinning effect of ZrSiO4 was responsible for the excellent oxidation protective ability of the coating. Moreover, Yao et al. [14] synthesized a ZrB2–SiC coating on carbon/carbon composites by a pack cementation process with Si, ZrB2 and B2O3 powders at 2173–2473 K. The excellent oxidation protective performance was attributed to the integrity and stability of SiO2 glass improved by the formation of ZrSiO4 phase during oxidation. Silicon carbide nanofibers have attracted considerable attention owing to their incredible mechanical and chemical properties, such as oxidation resistance, low thermal expansion, high thermal stability, high strength and low density and have been widely used as effective reinforcing elements in composites [15–18]. Zhang [19] indicated that the ZrB2-MoSi2/SiC coated carbon/carbon composites showed good anti-oxidation ability at 1273 K and selfsealing performance and oxidation resistance at 1773 K due to the SiC nano-whiskers covering the original cracks and the formation of ZrSiO4 and SiO2 glaze. Moreover, Li [20] and Chu [21] demonstrated
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Fig. 1. XRD patterns of: a) the first step coating, b) the second step coating.
that the SiC nanowires in the coating could efficiently suppress the cracking of the coating by various toughening mechanisms including nanowire pull out, nanowire bridging, microcrack deflection and the good interaction between nanowire/matrix interface, thus improving its protective ability against oxidation [22]. In the present paper, a multiphase protective coating consisting of functionally graded SiC, nanoSiC and ZrO2 was developed and the SiC nanofibers were formed in-situ by a novel pack cementation with Si, SiC, Al2O3 and ZrB2 powders and slurry painting methods at 1873 K. The phase compositions and microstructures of the prepared coating were studied and their oxidation resistance was also investigated at 1773 K in air.
Goodfellow), and 10 wt.% α-Al2O3 (800 mesh, Panadyne). The graphite samples were embedded in the powder mixture in a graphite crucible, and were then heat-treated at 1873 K for 2 h in an argon protective atmosphere to form the first step SiC coating. The second step coating was also prepared by the pack cementation technique with a powder mixture composed of 42 wt.% Si (400 mesh, Panadyne), 33 wt.% α-SiC (αSiC, 800 mesh, Goodfellow), 8 wt.% α-Al2O3 (800 mesh, Panadyne), and 17 wt.% ZrB2 (800 mesh, H.C. Starck), on the surface of the first step coated substrates then heated at 1873 K for 2 h in an argon protective atmosphere.
2. Experimental procedures
The isothermal oxidation test of the coated samples was performed at 1773 K in an electrical furnace. The cumulative weight changes of the coated samples after oxidation test were measured by a precision balance and recorded as a function of time. An X-ray diffractometer (XRD, Philips, PW1730) equipped with a copper X-ray source was used for the phase analysis of the coatings. The phases identification was performed by the X'Pert Highscore software developed by PANalytical B.V., and a field emission scanning electron microscope (SEM, Tescan, VEGAIII) operating at 20 kV and equipped with energy dispersive X-ray spectroscopy (EDS), secondary electrons detector (SE) and back scattered electrons detector (BSE) were used for the characterization of the coating morphologies.
2.1. Preparation of the coatings The specimens, with a dimension of 10 mm × 10 mm × 10 mm were cut from graphite with an apparent density of 2.07 g/cm3, a bulk density of 1.77 g/cm3, an apparent porosity of 14.56% and a flexural strength of 49.51 MPa. After being hand-abraded using 400 and 800 grit SiC paper, these specimens were cleaned with distilled ethanol and dried at 383 K for 2 h. The first step coating was formed on the surface of the graphite by the pack cementation technique with a powder mixture composed of 50 wt.% Si (400 mesh, Panadyne) 40 wt.% α-SiC (α-SiC, 800 mesh,
2.2. Characterization
Fig. 2. Cross section SEM images of: a) the first step coating, b) the second step coating.
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3. Results and discussion
ZrB2 reaction with the residual Oxygen in the furnace atmosphere.
3.1. Microstructure of the coating
ZrB2 þ 2:5O2 ðgÞ → ZrO2 þ B2 O3 ðlÞ
Fig. 1 shows the XRD patterns of the surface of the coatings. It can be seen that the first coating was composed of β-SiC, α-SiC and graphite. In order to propose the reaction-path mechanism for the formation of the SiC coating, it is worth noting that at the initial stages, Al2O3 present in the powder mixture can be reduced by C and Si. The SiC phase particles can be formed by the reactions of Si with C (Eq. (1)), Si with CO (Eq. (2)) and C with SiO (Eq. (3)), as established by other studies [23,24]. SiðlÞ þ C → SiC
ð1Þ
2Si þ COðgÞ → SiC þ SiOðgÞ
ð2Þ
SiOðgÞ þ 2C → SiC þ COðgÞ
ð3Þ
SiC was also formed by a reaction between SiO and CO gaseous phases according to Eq. (4). Regarding the presence of the carbon phase in the system, CO could be produced from CO2 by Eq. (5), and the reaction between SiO and CO could result in the production of SiC. In these conditions, SiC could be produced in the form of nanofibers, as indicated by other investigations [19]. SiOðgÞ þ 3COðgÞ → SiC þ 2CO2 ðgÞ
ð4Þ
2CO2 ðgÞ þ 2C → 4COðgÞ
ð5Þ
SiC crystal nuclei were generated by the reactions (1)–(3). It is believed that SiC crystal nuclei are suitable to be formed at the most active positions of the defects on the substrate. Afterwards, the formed SiC nuclei acted as seeding and interconnected to form SiC nanowires by the reaction (4) along the preferential crystalline direction, namely the (111) plane because of reasons based upon the lowest-energy principle [25]. As can be seen in Fig. 1, the second step coating composed of β-SiC and ZrO2 and a little amount of graphite. According to the Eq. (8), the production of ZrO2 phase by the ZrB2 precursor could be as a result of
3
ð6Þ
The B2O3 was not observed in the XRD analysis of the surface of the coating. It might have penetrated to the coating pores by the gravity-induced flow and transferred below the powders pack, or it might have been vaporized because of the high vapor pressure [19]. Moreover, Also, some B2O3 can react with SiO2 or dissolve into it, promoting the formation of a borosilicate glass with a higher melting point and lower vapor pressure and viscosity than those of the silica-scale alone [26]. Fig. 2 shows the scanning electron microscopy (SEM) images of the coatings. As can be seen, all of the coatings were gradual and without transverse cracks, and no discernible interface between the graphite substrate and the SiC coating was observed which indicates high bonding strength and good thermal compatibility between the coating and graphite substrate. A functionally graded C–SiC layer was formed at the graphite-coating interfaces with about 550 μm in thickness. By EDS analysis, the element distribution of the first step and the second step coatings are shown in Figs. 3 and 4, respectively. It can be seen that the outer SiC coating was extended with about 800 μm in thickness and the Zr element mainly focused in the outer layer. SEM images of the coatings surfaces are shown in Fig. 5. As can be observed, both coatings had two dimensions in the nanoscale recognized by ISO/TS 80004-4 [27] as a nanofiber. The nanofibers were corresponded to the SiC composition according to EDS element spot analysis in Fig. 5. Moreover, the number of SiC nanofibers was increased in the second step coating, and the diameter of these nanofibers was in the range of ~30–160 nm. Fig. 5 demonstrates that the SiC nanofibers bridged the coating microcracks and defects, thus inhibiting the promotion of defects subjected to thermal stresses and also, preventing the oxygen diffusion through the pores [19,21]. Fig. 6 shows the EDS mappings in the surface of the second coating. It can be clearly seen that the more uniformly coated regions are from the SiC mixture, whereas the ZrB2 regions were finer and less continuous.
3.2. The oxidation resistance of the coating Fig. 7 shows the weight loss of samples after isothermal oxidation at 1773 K in air for 10 h. It can be seen that through oxidation test, the
Fig. 3. EDS element line scan analysis of the first step coating.
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Fig. 4. EDS element line scan analysis of the second step coating.
Fig. 5. Surface backscattered electron SEM images and EDS element spot analysis of: a) the first step coating, b) the second step.
weight of the graphite without any coating quickly decreased linearly with time and the graphite substrate fully oxidized in less than 1 h caused by direct attack of oxygen on the graphite through pores; while the application of the first step coating resulted in an increase in the graphite oxidation resistance, but the weight loss of the first step coating was 70% after oxidation for 10 h and only a hollow crust with a small graphite core consisting of SiO2 and SiC remained. On the other hand, for the second step coating consisting of SiC-ZrO2, the weight loss of 11% was measured after oxidation for 10 h.
The XRD patterns of the surface of the coatings after oxidation at 1773 K for 10 h are shown in Fig. 8. After oxidation at 1773 K in air for 10 h, only a hollow crust with a small graphite core consisting of SiO2 and SiC was left from the first step coated sample. However, the second step coated sample was composed of β-SiC, ZrSiO4, and ZrO2 and SiO2. The following reactions could result in the oxidation of the coatings: 2C þ O2 ðgÞ → 2COðgÞ
Fig. 6. EDS mapping in the surface of the second coating: a) SEM image, b) Si mapping and c) Zr mapping.
Please cite this article as: J. Pourasad, et al., Surf. Coat. Technol. (2016), http://dx.doi.org/10.1016/j.surfcoat.2016.08.093
ð7Þ
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Fig. 7. Weight loss curves of samples after isothermal oxidation test at 1773 K: a) the first step coating, b) the second step, c) the graphite.
C þ O2 ðgÞ → CO2 ðgÞ
ð8Þ
SiC þ 2O2 ðgÞ → SiO2 þ CO2 ðgÞ
ð9Þ
2SiC þ 3O2 ðgÞ → 2SiO2 þ 2COðgÞ
ð10Þ
ZrO2 þ SiO2 ðlÞ → ZrSiO4
ð11Þ
As a consequence of the presence of carbon in both coatings, it seemed that oxygen could react with the carbon according to Eqs. (7) and (8). Thus, the carbon in the coating could be released with CO(g) and CO2(g) gases, leaving more pores behind for the diffusion of oxygen. Eqs. (7) and (8) lead to the reduction in the weight of the sample; therefore the weight loss after the oxidation could be attributed to these reactions [28]. Moreover, regarding the presence of the SiC phase in the coatings, it could be concluded that oxygen reacted with the SiC according to Eqs. (9) and (10), to form the SiO2 phase. Because the SiO2 glass phase has a melting point in the range of 1373–1923 K and a low vaporizing rate [28], the liquid SiO2 phase could fill the coating pores and since the coefficient of oxygen diffusion to the SiO2 glass phase at 1773 K is very low [29], the SiO2 liquid phase could prevent the diffusion of oxygen to the coating. Therefore, the oxidation process was controlled by the diffusion of oxygen through the coating pores and the coating oxidation was prevented [30]. Also, the oxidation of ZrB2 by reaction (6) can produce molten-B2O3 and ZrO2. As a result, the oxides generated on the surface of the coating, result in the increase of the
5
total weight [28]. The small weight gain of the second step coating after oxidation for 2 h according to Fig. 7 could be caused by the formation of ZrSiO4 and SiO2 due to the oxidation of SiC and ZrB2 on the surface. According to the Eq. (11), the ZrO2 phase could react with SiO2 in the second step coating [31], thus forming a refractory zircon phase (ZrSiO4) which is beneficial to oxidation resistance ability because of its low permeability of oxygen and high thermal stability at high temperature [12,32]. Consequently, the good oxidation resistance of the second step coating could be attributed to the ZrSiO4 formation. Fig. 9 shows the cross section SEM images of the coating after oxidation at 1773 K in air. As can be seen, the cross section of the first coating sample exhibited a delamination defect which could be because of the thermal stress induced by the mismatch of the thermal expansion coefficient between the resulting SiO2 and the substrate. (αgraphite = 2.3 × 10−6 K−1 (with grain) and 3.4 × 10−6 K−1 (across grain) [33], αSiC = 4.5 × 10− 6 K− 1, αSiO2 = 0.5 × 10− 6 K−1 [12], αZrSiO4 = 5.5 × 10−6 K−1 [34]). When the SiO2 layer is relatively thin, the good bond strength between the coating layer and the graphite substrate is maintained. As the thickness of the coating layer increases, the stress caused by the mismatch of the thermal expansion coefficient is ultimately increased, resulting in the exhibition of the delamination defect [35]. Whereas, the second coated sample due to the formation of ZrSiO4 and the presence of nanofibers was completely reserved with its gradient structure. SEM images of the samples surface and EDS element spot analysis after oxidation at 1773 K are shown in Fig. 10. As can be seen, the coatings were covered by dense SiO2 glass phase produced due to SiC oxidation. The first step coating had the most surface pores, while the pores of the second step coating had filled with an apparently glass phase. It seemed that there was a direct relationship between the amounts of pores and the weight reduction, since the higher the surface pores, the more the oxygen diffused to the lower parts of the coating; therefore the more the oxidization of graphite, the more the increase in the percentage reduction in the total weight. It seemed that the SiC nanofibers bridged the microcracks of the coating thus inhibiting the promotion of defects subjected to thermal stresses and preventing the oxygen diffusion through the pores. It is suggested that the formation mechanism of nanofibers can be studied in the future studies. 4. Conclusions A nanostructured SiC/SiC-ZrO2 coating was successfully prepared by a two-step pack cementation technique to improve oxidation resistance of graphite substrate. The first step coating was composed of a 550 μm thick functionally graded SiC coating. The second step coating consisted of SiC-ZrO2 produced by a novel pack cementation method. The oxidation resistance of the coating was surveyed at 1773 K in air for 10 h. After oxidation at 1773 K, the graphite substrate without coating was
Fig. 8. XRD patterns of the coatings after oxidation for 10 h: a) the first step coating, b) the second step coating.
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Fig. 9. Cross section SEM images of the samples after oxidation for 10 h: a) the first step coating, b) the second step coating.
Fig. 10. Surface SEM images and EDS element spot analysis of the samples after oxidation for 10 h: a) the first step coating, b) the second step coating.
fully oxidized in less than 1 h. The results related to the weight change of the samples revealed that the SiC-ZrO2 coating played an effective role in increasing the oxidation resistance of the graphite. After oxidation for 10 h, the weight loss of the first step coating was 70% and only a hollow crust with a small graphite core consisting of SiO2 and SiC remained; however, the weight loss of the second step was 11%. The excellent protection ability SiC-ZrO2 coating could be attributed to the formation of the SiC nanofibers, SiO2 glass layer and somewhat ZrSiO4.
References [1] E. Fitzer, Carbon Reinforcements and Carbon/Carbon Composites, Springer, Berlin, Heidelberg, 1998. [2] Y. Chu, Q. Fu, C. Cao, H. Li, K. Li, Q. Lei, Microstructure and oxidation resistant property of C/C composites modified by SiC–MoSi2–CrSi2 coating, Surf. Eng. 27 (2011) 355–361. [3] H. Jin, S. Meng, X. Zhang, Q. Zeng, J. Niu, Effects of oxidation temperature, time, and ambient pressure on the oxidation of ZrB2–SiC–graphite composites in atomic oxygen, J. Eur. Ceram. Soc. 36 (2016) 1855–1861. [4] T. Feng, H. Li, M. Hu, H. Lin, L. Li, Oxidation and ablation resistance of the ZrB2–CrSi2– Si/SiC coating for C/C composites at high temperature, J. Alloys Compd. 662 (2016) 302–307. [5] J.W. Park, E.S. Kim, J.U. Kim, Y. Kim, W.E. Windes, Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature, Appl. Surf. Sci. 378 (2016) 341–349. [6] B. Paul, J. Prakash, P. Sarkar, Formation and characterization of uniform SiC coating on 3-D graphite substrate using halide activated pack cementation method, Surf. Coat. Technol. 282 (2015) 61–67. [7] J.P. Zhang, Q.G. Fu, J.L. Qu, L. Zhuang, P.P. Wang, H.J. Li, An inlaid interface of carbon/ carbon composites to enhance the thermal shock resistance of SiC coating in combustion environment, Surf. Coat. Technol. 294 (2016) 95–101. [8] J. Pourasad, N. Ehsani, In-situ synthesis of SiC nanofibers for improving the oxidation resistance of graphite, Ceram. Int. 42 (2016) 14730–14737. [9] P. Wang, C. Zhou, X. Zhang, G. Zhao, B. Xu, Y. Cheng, P. Zhou, W. Han, Oxidation protective ZrB2–SiC coatings with ferrocene addition on SiC coated graphite, Ceram. Int. 42 (2016) 2654–2661. [10] L. Li, H. Li, Y. Li, X. Yin, Q. Shen, Q. Fu, A SiC-ZrB2-ZrC coating toughened by electrophoretically-deposited SiC nanowires to protect C/C composites against thermal shock and oxidation, Appl. Surf. Sci. 349 (2015) 465–471.
[11] J.-P. Zhang, Q.-G. Fu, P.-F. Zhang, J.-L. Qu, R.-M. Yuan, H.-J. Li, Rapid heat treatment to improve the thermal shock resistance of ZrO2 coating for SiC coated carbon/carbon composites, Surf. Coat. Technol. 285 (2016) 24–30. [12] P. Wang, W. Han, X. Zhang, N. Li, G. Zhao, S. Zhou, (ZrB2–SiC)/SiC oxidation protective coatings for graphite materials, Ceram. Int. 41 (2015) 6941–6949. [13] X. Ren, H. Li, Y. Chu, K. Li, Q. Fu, ZrB2–SiC gradient oxidation protective coating for carbon/carbon composites, Ceram. Int. 40 (2014) 7171–7176. [14] X. Yao, H. Li, Y. Zhang, H. Wu, X. Qiang, A SiC–Si–ZrB2 multiphase oxidation protective ceramic coating for SiC-coated carbon/carbon composites, Ceram. Int. 38 (2012) 2095–2100. [15] J. Fan, P.K.-H. Chu, Silicon Carbide Nanostructures: Fabrication, Structure, and Properties, Springer, 2014. [16] H.-f. Wang, Y.-b. Bi, N.-s. Zhou, H.-j. Zhang, Preparation and strength of SiC refractories with in situ β-SiC whiskers as bonding phase, Ceram. Int. 42 (2016) 727–733. [17] H. Mei, H. Wang, H. Ding, N. Zhang, Y. Wang, S. Xiao, Q. Bai, L. Cheng, Strength and toughness improvement in a C/SiC composite reinforced with slurry-prone SiC whiskers, Ceram. Int. 40 (2014) 14099–14104. [18] J. Pourasad, N. Ehsani, S.A. Khalifesoltani, Preparation and characterization of SiO2 thin film and SiC nanofibers to improve of graphite oxidation resistance, J. Eur. Ceram. Soc. 36 (2016) 3947–3956. [19] W.Z. Zhang, Z. Yi, L. Gbologah, X. Xiong, B.Y. Huang, Preparation and oxidation property of ZrB2-MoSi2/SiC coating on carbon/carbon composites, Trans. Nonferrous Metals Soc. China 21 (2011) 1538–1544. [20] H.J. Li, Y.L. Zhang, Q.G. Fu, K.Z. Li, J. Wei, D.S. Hou, Oxidation behavior of SiC nanoparticle-SiC oxidation protective coating for carbon/carbon composites at 1773 K, Carbon 45 (2007) 2704–2707. [21] Y. Chu, H. Li, Q. Fu, H. Wang, X. Hou, X. Zou, G. Shang, Oxidation protection of C/C composites with a multilayer coating of SiC and Si + SiC + SiC nanowires, Carbon 50 (2012) 1280–1288. [22] S. Gurbán, L. Kotis, A. Pongrácz, A. Sulyok, A.L. Tóth, E. Vázsonyi, M. Menyhárd, The chemical resistance of nano-sized SiC rich composite coating, Surf. Coat. Technol. 261 (2015) 195–200. [23] J.H. Kang, H.M. Cha, J.H. Lee, Y.G. Jung, H.S. Lee, V. Srivastava, Synthesis and characterization of non-oxide ceramic coatings on graphite substrates by solid–vapor reaction process, Prog. Org. Coat. 61 (2008) 291–299. [24] O. Paccaud, A. Derre, Silicon carbide coating by reactive pack cementation—part II: silicon monoxide/carbon reaction, Chem. Vap. Depos. 6 (2000) 41–50. [25] K. Chen, Z. Huang, J. Huang, M. Fang, Y.-g. Liu, H. Ji, L. Yin, Synthesis of SiC nanowires by thermal evaporation method without catalyst assistant, Ceram. Int. 39 (2013) 1957–1962. [26] X. Yang, L. Wei, W. Song, Z. Bi-feng, C. Zhao-hui, ZrB2/SiC as a protective coating for C/SiC composites: effect of high temperature oxidation on mechanical properties and anti-ablation property, Compos. Part B 45 (2013) 1391–1396.
Please cite this article as: J. Pourasad, et al., Surf. Coat. Technol. (2016), http://dx.doi.org/10.1016/j.surfcoat.2016.08.093
J. Pourasad et al. / Surface & Coatings Technology xxx (2016) xxx–xxx [27] ISO/TS 80004–4-2011, Nanotechnologies-Vocabulary-Part 4: Nanostructured Materials, International Organization for Standardization, ISO/TC229, Geneva, Switzerland, 2011. [28] F. Tao, L. He Jun, S. Xiao Hong, Y. Xi, W. Shao Long, Oxidation and ablation resistance of ZrB2―SiC―Si/B-modified SiC coating for carbon/carbon composites, Corros. Sci. 67 (2013) 292–297. [29] Y.L. Zhang, H.J. Li, X.Y. Yao, K.Z. Li, S.Y. Zhang, C/SiC/Si-Mo-B/glass multilayer oxidation protective coating for carbon/carbon composites, Surf. Coat. Technol. 206 (2011) 492–496. [30] X. Yang, Y.h. Zou, Q.Z. Huang, Z.A. Su, X. Chang, M.Y. Zhang, Y. Xiao, Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites, J. Cent. S. Univ. Technol. 17 (2010) 1–6.
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[31] C. Wang, J.-M. Yang, W. Hoffman, Thermal stability of refractory carbide/boride composites, Mater. Chem. Phys. 74 (2002) 272–281. [32] A. Kaiser, M. Lobert, R. Telle, Thermal stability of zircon (ZrSiO4), J. Eur. Ceram. Soc. 28 (2008) 2199–2211. [33] P. Morgan, Carbon Fibers and Their Composites, Taylor & Francis, Boca Raton, 2005. [34] J.F. Shackelford, W. Alexander, CRC Materials Science and Engineering Handbook, CRC press, Boca Raton, 2000. [35] O.S. Kwon, S.H. Hong, H. Kim, The improvement in oxidation resistance of carbon by a graded SiC/SiO2 coating, J. Eur. Ceram. Soc. 23 (2003) 3119–3124.
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Preparation of a nanostructured SiC-ZrO2 coating to improve the oxidation resistance of graphite Jalil Pourasad ⁎, Naser Ehsani, Zia Valefi, Sayed Ali Khalifesoltani Faculty of Materials and Manufacturing Technology, Malek-Ashtar University of Technology, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 16 June 2016 Revised 22 August 2016 Accepted in revised form 31 August 2016 Available online xxxx Keywords: Graphite Oxidation resistance Nanostructure SiC ZrO2 Pack cementation
a b s t r a c t A nanostructured SiC/SiC-ZrO2 coating was prepared on a graphite substrate by a two-step technique to improve the oxidation protection ability of graphite. The first step was to prepare a functionally graded SiC layer by a pack cementation process and the second one was to obtain a SiC-ZrO2 coating through a pack cementation technique at 1873 K. The phase compositions and microstructure of the coating were characterized by X-ray diffraction and scanning electron microscopy. The isothermal oxidation test of the coated samples was performed at 1773 K for 10 h. A gradient C–SiC transition layer can be observed at the graphite-coating interface and a SiC-ZrO2 coating was formed. The SiC nanofibers with the diameter in the range of 30–160 nm were observed on the coating. The SiC-ZrO2 coating could efficiently improve oxidation resistance of graphite with a weight loss of 11%, as compared with a 70% weight loss of the first step coating. © 2016 Published by Elsevier B.V.
1. Introduction Carbon/carbon materials and graphite were known to be widely used for high temperature structural applications such as aero engine and turbine components due to the maintenance of their mechanical and thermal properties. However, the oxidation of carbon-based materials above 773 K in air cannot meet the request of practical application requirement, specifically for high-temperature causing a fall in their mechanical properties. Certainly, with the increase in oxidation temperature, the rate of graphite chemical reaction with oxygen, as well as the extent of oxidation, is extremely increased. Therefore, more studies have been conducted in an attempt to protect graphite against oxidation [1–3]. It is well known that the SiC coating is an effective method for protecting graphite at high temperature, since it can significantly avoid the oxygen diffusion into the graphite by producing a protective layer. In addition, the glass SiO2 film will be formed on the surface of the coating while the SiC coated graphite is placed in air at high temperature, which can efficiently inhibit oxygen from diffusing into the graphite. However, the mismatch of the thermal expansion coefficient between graphite and the SiC coating commonly lead to cracking of SiC coating, facilitating the oxygen diffusion to graphite substrate and the failure of the coating. Therefore, the protective temperature range of SiC coating is narrow, which limits the coating application for protection of graphite against oxidation [4–8]. ZrB2–SiC ceramic coating is a promising solution to improve ablation property of the graphite. The ⁎ Corresponding author. E-mail address: [email protected] (J. Pourasad).
ZrO2 produced by oxidation of ZrB2 can react with SiO2 to form ZrSiO4, which is beneficial to oxidation resistance ability due to its low permeability for oxygen and high thermal stability at high temperature. The high-thermally stable ZrSiO4 can be expected to reduce the consumption of SiO2 and improve the oxidation resistance of SiC coating at high temperature [9–11]. Wang et al. [12] used a two-step pack cementation method with ZrB2, Si and graphite powders at 2273 K to prepare ZrB2–SiC coating on graphite, which showed (ZrB2–SiC)/SiC coatings can better protect the graphite matrix than SiC coating from oxidation. Ren et al. [13] prepared a ZrB2–SiC gradient coating by a pack cementation process with Si, ZrO2, B2O3 and graphite powders at 2373 K. The effective self-sealing property of the protective silicate glass layer as well as the pinning effect of ZrSiO4 was responsible for the excellent oxidation protective ability of the coating. Moreover, Yao et al. [14] synthesized a ZrB2–SiC coating on carbon/carbon composites by a pack cementation process with Si, ZrB2 and B2O3 powders at 2173–2473 K. The excellent oxidation protective performance was attributed to the integrity and stability of SiO2 glass improved by the formation of ZrSiO4 phase during oxidation. Silicon carbide nanofibers have attracted considerable attention owing to their incredible mechanical and chemical properties, such as oxidation resistance, low thermal expansion, high thermal stability, high strength and low density and have been widely used as effective reinforcing elements in composites [15–18]. Zhang [19] indicated that the ZrB2-MoSi2/SiC coated carbon/carbon composites showed good anti-oxidation ability at 1273 K and selfsealing performance and oxidation resistance at 1773 K due to the SiC nano-whiskers covering the original cracks and the formation of ZrSiO4 and SiO2 glaze. Moreover, Li [20] and Chu [21] demonstrated
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Fig. 1. XRD patterns of: a) the first step coating, b) the second step coating.
that the SiC nanowires in the coating could efficiently suppress the cracking of the coating by various toughening mechanisms including nanowire pull out, nanowire bridging, microcrack deflection and the good interaction between nanowire/matrix interface, thus improving its protective ability against oxidation [22]. In the present paper, a multiphase protective coating consisting of functionally graded SiC, nanoSiC and ZrO2 was developed and the SiC nanofibers were formed in-situ by a novel pack cementation with Si, SiC, Al2O3 and ZrB2 powders and slurry painting methods at 1873 K. The phase compositions and microstructures of the prepared coating were studied and their oxidation resistance was also investigated at 1773 K in air.
Goodfellow), and 10 wt.% α-Al2O3 (800 mesh, Panadyne). The graphite samples were embedded in the powder mixture in a graphite crucible, and were then heat-treated at 1873 K for 2 h in an argon protective atmosphere to form the first step SiC coating. The second step coating was also prepared by the pack cementation technique with a powder mixture composed of 42 wt.% Si (400 mesh, Panadyne), 33 wt.% α-SiC (αSiC, 800 mesh, Goodfellow), 8 wt.% α-Al2O3 (800 mesh, Panadyne), and 17 wt.% ZrB2 (800 mesh, H.C. Starck), on the surface of the first step coated substrates then heated at 1873 K for 2 h in an argon protective atmosphere.
2. Experimental procedures
The isothermal oxidation test of the coated samples was performed at 1773 K in an electrical furnace. The cumulative weight changes of the coated samples after oxidation test were measured by a precision balance and recorded as a function of time. An X-ray diffractometer (XRD, Philips, PW1730) equipped with a copper X-ray source was used for the phase analysis of the coatings. The phases identification was performed by the X'Pert Highscore software developed by PANalytical B.V., and a field emission scanning electron microscope (SEM, Tescan, VEGAIII) operating at 20 kV and equipped with energy dispersive X-ray spectroscopy (EDS), secondary electrons detector (SE) and back scattered electrons detector (BSE) were used for the characterization of the coating morphologies.
2.1. Preparation of the coatings The specimens, with a dimension of 10 mm × 10 mm × 10 mm were cut from graphite with an apparent density of 2.07 g/cm3, a bulk density of 1.77 g/cm3, an apparent porosity of 14.56% and a flexural strength of 49.51 MPa. After being hand-abraded using 400 and 800 grit SiC paper, these specimens were cleaned with distilled ethanol and dried at 383 K for 2 h. The first step coating was formed on the surface of the graphite by the pack cementation technique with a powder mixture composed of 50 wt.% Si (400 mesh, Panadyne) 40 wt.% α-SiC (α-SiC, 800 mesh,
2.2. Characterization
Fig. 2. Cross section SEM images of: a) the first step coating, b) the second step coating.
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3. Results and discussion
ZrB2 reaction with the residual Oxygen in the furnace atmosphere.
3.1. Microstructure of the coating
ZrB2 þ 2:5O2 ðgÞ → ZrO2 þ B2 O3 ðlÞ
Fig. 1 shows the XRD patterns of the surface of the coatings. It can be seen that the first coating was composed of β-SiC, α-SiC and graphite. In order to propose the reaction-path mechanism for the formation of the SiC coating, it is worth noting that at the initial stages, Al2O3 present in the powder mixture can be reduced by C and Si. The SiC phase particles can be formed by the reactions of Si with C (Eq. (1)), Si with CO (Eq. (2)) and C with SiO (Eq. (3)), as established by other studies [23,24]. SiðlÞ þ C → SiC
ð1Þ
2Si þ COðgÞ → SiC þ SiOðgÞ
ð2Þ
SiOðgÞ þ 2C → SiC þ COðgÞ
ð3Þ
SiC was also formed by a reaction between SiO and CO gaseous phases according to Eq. (4). Regarding the presence of the carbon phase in the system, CO could be produced from CO2 by Eq. (5), and the reaction between SiO and CO could result in the production of SiC. In these conditions, SiC could be produced in the form of nanofibers, as indicated by other investigations [19]. SiOðgÞ þ 3COðgÞ → SiC þ 2CO2 ðgÞ
ð4Þ
2CO2 ðgÞ þ 2C → 4COðgÞ
ð5Þ
SiC crystal nuclei were generated by the reactions (1)–(3). It is believed that SiC crystal nuclei are suitable to be formed at the most active positions of the defects on the substrate. Afterwards, the formed SiC nuclei acted as seeding and interconnected to form SiC nanowires by the reaction (4) along the preferential crystalline direction, namely the (111) plane because of reasons based upon the lowest-energy principle [25]. As can be seen in Fig. 1, the second step coating composed of β-SiC and ZrO2 and a little amount of graphite. According to the Eq. (8), the production of ZrO2 phase by the ZrB2 precursor could be as a result of
3
ð6Þ
The B2O3 was not observed in the XRD analysis of the surface of the coating. It might have penetrated to the coating pores by the gravity-induced flow and transferred below the powders pack, or it might have been vaporized because of the high vapor pressure [19]. Moreover, Also, some B2O3 can react with SiO2 or dissolve into it, promoting the formation of a borosilicate glass with a higher melting point and lower vapor pressure and viscosity than those of the silica-scale alone [26]. Fig. 2 shows the scanning electron microscopy (SEM) images of the coatings. As can be seen, all of the coatings were gradual and without transverse cracks, and no discernible interface between the graphite substrate and the SiC coating was observed which indicates high bonding strength and good thermal compatibility between the coating and graphite substrate. A functionally graded C–SiC layer was formed at the graphite-coating interfaces with about 550 μm in thickness. By EDS analysis, the element distribution of the first step and the second step coatings are shown in Figs. 3 and 4, respectively. It can be seen that the outer SiC coating was extended with about 800 μm in thickness and the Zr element mainly focused in the outer layer. SEM images of the coatings surfaces are shown in Fig. 5. As can be observed, both coatings had two dimensions in the nanoscale recognized by ISO/TS 80004-4 [27] as a nanofiber. The nanofibers were corresponded to the SiC composition according to EDS element spot analysis in Fig. 5. Moreover, the number of SiC nanofibers was increased in the second step coating, and the diameter of these nanofibers was in the range of ~30–160 nm. Fig. 5 demonstrates that the SiC nanofibers bridged the coating microcracks and defects, thus inhibiting the promotion of defects subjected to thermal stresses and also, preventing the oxygen diffusion through the pores [19,21]. Fig. 6 shows the EDS mappings in the surface of the second coating. It can be clearly seen that the more uniformly coated regions are from the SiC mixture, whereas the ZrB2 regions were finer and less continuous.
3.2. The oxidation resistance of the coating Fig. 7 shows the weight loss of samples after isothermal oxidation at 1773 K in air for 10 h. It can be seen that through oxidation test, the
Fig. 3. EDS element line scan analysis of the first step coating.
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Fig. 4. EDS element line scan analysis of the second step coating.
Fig. 5. Surface backscattered electron SEM images and EDS element spot analysis of: a) the first step coating, b) the second step.
weight of the graphite without any coating quickly decreased linearly with time and the graphite substrate fully oxidized in less than 1 h caused by direct attack of oxygen on the graphite through pores; while the application of the first step coating resulted in an increase in the graphite oxidation resistance, but the weight loss of the first step coating was 70% after oxidation for 10 h and only a hollow crust with a small graphite core consisting of SiO2 and SiC remained. On the other hand, for the second step coating consisting of SiC-ZrO2, the weight loss of 11% was measured after oxidation for 10 h.
The XRD patterns of the surface of the coatings after oxidation at 1773 K for 10 h are shown in Fig. 8. After oxidation at 1773 K in air for 10 h, only a hollow crust with a small graphite core consisting of SiO2 and SiC was left from the first step coated sample. However, the second step coated sample was composed of β-SiC, ZrSiO4, and ZrO2 and SiO2. The following reactions could result in the oxidation of the coatings: 2C þ O2 ðgÞ → 2COðgÞ
Fig. 6. EDS mapping in the surface of the second coating: a) SEM image, b) Si mapping and c) Zr mapping.
Please cite this article as: J. Pourasad, et al., Surf. Coat. Technol. (2016), http://dx.doi.org/10.1016/j.surfcoat.2016.08.093
ð7Þ
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Fig. 7. Weight loss curves of samples after isothermal oxidation test at 1773 K: a) the first step coating, b) the second step, c) the graphite.
C þ O2 ðgÞ → CO2 ðgÞ
ð8Þ
SiC þ 2O2 ðgÞ → SiO2 þ CO2 ðgÞ
ð9Þ
2SiC þ 3O2 ðgÞ → 2SiO2 þ 2COðgÞ
ð10Þ
ZrO2 þ SiO2 ðlÞ → ZrSiO4
ð11Þ
As a consequence of the presence of carbon in both coatings, it seemed that oxygen could react with the carbon according to Eqs. (7) and (8). Thus, the carbon in the coating could be released with CO(g) and CO2(g) gases, leaving more pores behind for the diffusion of oxygen. Eqs. (7) and (8) lead to the reduction in the weight of the sample; therefore the weight loss after the oxidation could be attributed to these reactions [28]. Moreover, regarding the presence of the SiC phase in the coatings, it could be concluded that oxygen reacted with the SiC according to Eqs. (9) and (10), to form the SiO2 phase. Because the SiO2 glass phase has a melting point in the range of 1373–1923 K and a low vaporizing rate [28], the liquid SiO2 phase could fill the coating pores and since the coefficient of oxygen diffusion to the SiO2 glass phase at 1773 K is very low [29], the SiO2 liquid phase could prevent the diffusion of oxygen to the coating. Therefore, the oxidation process was controlled by the diffusion of oxygen through the coating pores and the coating oxidation was prevented [30]. Also, the oxidation of ZrB2 by reaction (6) can produce molten-B2O3 and ZrO2. As a result, the oxides generated on the surface of the coating, result in the increase of the
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total weight [28]. The small weight gain of the second step coating after oxidation for 2 h according to Fig. 7 could be caused by the formation of ZrSiO4 and SiO2 due to the oxidation of SiC and ZrB2 on the surface. According to the Eq. (11), the ZrO2 phase could react with SiO2 in the second step coating [31], thus forming a refractory zircon phase (ZrSiO4) which is beneficial to oxidation resistance ability because of its low permeability of oxygen and high thermal stability at high temperature [12,32]. Consequently, the good oxidation resistance of the second step coating could be attributed to the ZrSiO4 formation. Fig. 9 shows the cross section SEM images of the coating after oxidation at 1773 K in air. As can be seen, the cross section of the first coating sample exhibited a delamination defect which could be because of the thermal stress induced by the mismatch of the thermal expansion coefficient between the resulting SiO2 and the substrate. (αgraphite = 2.3 × 10−6 K−1 (with grain) and 3.4 × 10−6 K−1 (across grain) [33], αSiC = 4.5 × 10− 6 K− 1, αSiO2 = 0.5 × 10− 6 K−1 [12], αZrSiO4 = 5.5 × 10−6 K−1 [34]). When the SiO2 layer is relatively thin, the good bond strength between the coating layer and the graphite substrate is maintained. As the thickness of the coating layer increases, the stress caused by the mismatch of the thermal expansion coefficient is ultimately increased, resulting in the exhibition of the delamination defect [35]. Whereas, the second coated sample due to the formation of ZrSiO4 and the presence of nanofibers was completely reserved with its gradient structure. SEM images of the samples surface and EDS element spot analysis after oxidation at 1773 K are shown in Fig. 10. As can be seen, the coatings were covered by dense SiO2 glass phase produced due to SiC oxidation. The first step coating had the most surface pores, while the pores of the second step coating had filled with an apparently glass phase. It seemed that there was a direct relationship between the amounts of pores and the weight reduction, since the higher the surface pores, the more the oxygen diffused to the lower parts of the coating; therefore the more the oxidization of graphite, the more the increase in the percentage reduction in the total weight. It seemed that the SiC nanofibers bridged the microcracks of the coating thus inhibiting the promotion of defects subjected to thermal stresses and preventing the oxygen diffusion through the pores. It is suggested that the formation mechanism of nanofibers can be studied in the future studies. 4. Conclusions A nanostructured SiC/SiC-ZrO2 coating was successfully prepared by a two-step pack cementation technique to improve oxidation resistance of graphite substrate. The first step coating was composed of a 550 μm thick functionally graded SiC coating. The second step coating consisted of SiC-ZrO2 produced by a novel pack cementation method. The oxidation resistance of the coating was surveyed at 1773 K in air for 10 h. After oxidation at 1773 K, the graphite substrate without coating was
Fig. 8. XRD patterns of the coatings after oxidation for 10 h: a) the first step coating, b) the second step coating.
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Fig. 9. Cross section SEM images of the samples after oxidation for 10 h: a) the first step coating, b) the second step coating.
Fig. 10. Surface SEM images and EDS element spot analysis of the samples after oxidation for 10 h: a) the first step coating, b) the second step coating.
fully oxidized in less than 1 h. The results related to the weight change of the samples revealed that the SiC-ZrO2 coating played an effective role in increasing the oxidation resistance of the graphite. After oxidation for 10 h, the weight loss of the first step coating was 70% and only a hollow crust with a small graphite core consisting of SiO2 and SiC remained; however, the weight loss of the second step was 11%. The excellent protection ability SiC-ZrO2 coating could be attributed to the formation of the SiC nanofibers, SiO2 glass layer and somewhat ZrSiO4.
References [1] E. Fitzer, Carbon Reinforcements and Carbon/Carbon Composites, Springer, Berlin, Heidelberg, 1998. [2] Y. Chu, Q. Fu, C. Cao, H. Li, K. Li, Q. Lei, Microstructure and oxidation resistant property of C/C composites modified by SiC–MoSi2–CrSi2 coating, Surf. Eng. 27 (2011) 355–361. [3] H. Jin, S. Meng, X. Zhang, Q. Zeng, J. Niu, Effects of oxidation temperature, time, and ambient pressure on the oxidation of ZrB2–SiC–graphite composites in atomic oxygen, J. Eur. Ceram. Soc. 36 (2016) 1855–1861. [4] T. Feng, H. Li, M. Hu, H. Lin, L. Li, Oxidation and ablation resistance of the ZrB2–CrSi2– Si/SiC coating for C/C composites at high temperature, J. Alloys Compd. 662 (2016) 302–307. [5] J.W. Park, E.S. Kim, J.U. Kim, Y. Kim, W.E. Windes, Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature, Appl. Surf. Sci. 378 (2016) 341–349. [6] B. Paul, J. Prakash, P. Sarkar, Formation and characterization of uniform SiC coating on 3-D graphite substrate using halide activated pack cementation method, Surf. Coat. Technol. 282 (2015) 61–67. [7] J.P. Zhang, Q.G. Fu, J.L. Qu, L. Zhuang, P.P. Wang, H.J. Li, An inlaid interface of carbon/ carbon composites to enhance the thermal shock resistance of SiC coating in combustion environment, Surf. Coat. Technol. 294 (2016) 95–101. [8] J. Pourasad, N. Ehsani, In-situ synthesis of SiC nanofibers for improving the oxidation resistance of graphite, Ceram. Int. 42 (2016) 14730–14737. [9] P. Wang, C. Zhou, X. Zhang, G. Zhao, B. Xu, Y. Cheng, P. Zhou, W. Han, Oxidation protective ZrB2–SiC coatings with ferrocene addition on SiC coated graphite, Ceram. Int. 42 (2016) 2654–2661. [10] L. Li, H. Li, Y. Li, X. Yin, Q. Shen, Q. Fu, A SiC-ZrB2-ZrC coating toughened by electrophoretically-deposited SiC nanowires to protect C/C composites against thermal shock and oxidation, Appl. Surf. Sci. 349 (2015) 465–471.
[11] J.-P. Zhang, Q.-G. Fu, P.-F. Zhang, J.-L. Qu, R.-M. Yuan, H.-J. Li, Rapid heat treatment to improve the thermal shock resistance of ZrO2 coating for SiC coated carbon/carbon composites, Surf. Coat. Technol. 285 (2016) 24–30. [12] P. Wang, W. Han, X. Zhang, N. Li, G. Zhao, S. Zhou, (ZrB2–SiC)/SiC oxidation protective coatings for graphite materials, Ceram. Int. 41 (2015) 6941–6949. [13] X. Ren, H. Li, Y. Chu, K. Li, Q. Fu, ZrB2–SiC gradient oxidation protective coating for carbon/carbon composites, Ceram. Int. 40 (2014) 7171–7176. [14] X. Yao, H. Li, Y. Zhang, H. Wu, X. Qiang, A SiC–Si–ZrB2 multiphase oxidation protective ceramic coating for SiC-coated carbon/carbon composites, Ceram. Int. 38 (2012) 2095–2100. [15] J. Fan, P.K.-H. Chu, Silicon Carbide Nanostructures: Fabrication, Structure, and Properties, Springer, 2014. [16] H.-f. Wang, Y.-b. Bi, N.-s. Zhou, H.-j. Zhang, Preparation and strength of SiC refractories with in situ β-SiC whiskers as bonding phase, Ceram. Int. 42 (2016) 727–733. [17] H. Mei, H. Wang, H. Ding, N. Zhang, Y. Wang, S. Xiao, Q. Bai, L. Cheng, Strength and toughness improvement in a C/SiC composite reinforced with slurry-prone SiC whiskers, Ceram. Int. 40 (2014) 14099–14104. [18] J. Pourasad, N. Ehsani, S.A. Khalifesoltani, Preparation and characterization of SiO2 thin film and SiC nanofibers to improve of graphite oxidation resistance, J. Eur. Ceram. Soc. 36 (2016) 3947–3956. [19] W.Z. Zhang, Z. Yi, L. Gbologah, X. Xiong, B.Y. Huang, Preparation and oxidation property of ZrB2-MoSi2/SiC coating on carbon/carbon composites, Trans. Nonferrous Metals Soc. China 21 (2011) 1538–1544. [20] H.J. Li, Y.L. Zhang, Q.G. Fu, K.Z. Li, J. Wei, D.S. Hou, Oxidation behavior of SiC nanoparticle-SiC oxidation protective coating for carbon/carbon composites at 1773 K, Carbon 45 (2007) 2704–2707. [21] Y. Chu, H. Li, Q. Fu, H. Wang, X. Hou, X. Zou, G. Shang, Oxidation protection of C/C composites with a multilayer coating of SiC and Si + SiC + SiC nanowires, Carbon 50 (2012) 1280–1288. [22] S. Gurbán, L. Kotis, A. Pongrácz, A. Sulyok, A.L. Tóth, E. Vázsonyi, M. Menyhárd, The chemical resistance of nano-sized SiC rich composite coating, Surf. Coat. Technol. 261 (2015) 195–200. [23] J.H. Kang, H.M. Cha, J.H. Lee, Y.G. Jung, H.S. Lee, V. Srivastava, Synthesis and characterization of non-oxide ceramic coatings on graphite substrates by solid–vapor reaction process, Prog. Org. Coat. 61 (2008) 291–299. [24] O. Paccaud, A. Derre, Silicon carbide coating by reactive pack cementation—part II: silicon monoxide/carbon reaction, Chem. Vap. Depos. 6 (2000) 41–50. [25] K. Chen, Z. Huang, J. Huang, M. Fang, Y.-g. Liu, H. Ji, L. Yin, Synthesis of SiC nanowires by thermal evaporation method without catalyst assistant, Ceram. Int. 39 (2013) 1957–1962. [26] X. Yang, L. Wei, W. Song, Z. Bi-feng, C. Zhao-hui, ZrB2/SiC as a protective coating for C/SiC composites: effect of high temperature oxidation on mechanical properties and anti-ablation property, Compos. Part B 45 (2013) 1391–1396.
Please cite this article as: J. Pourasad, et al., Surf. Coat. Technol. (2016), http://dx.doi.org/10.1016/j.surfcoat.2016.08.093
J. Pourasad et al. / Surface & Coatings Technology xxx (2016) xxx–xxx [27] ISO/TS 80004–4-2011, Nanotechnologies-Vocabulary-Part 4: Nanostructured Materials, International Organization for Standardization, ISO/TC229, Geneva, Switzerland, 2011. [28] F. Tao, L. He Jun, S. Xiao Hong, Y. Xi, W. Shao Long, Oxidation and ablation resistance of ZrB2―SiC―Si/B-modified SiC coating for carbon/carbon composites, Corros. Sci. 67 (2013) 292–297. [29] Y.L. Zhang, H.J. Li, X.Y. Yao, K.Z. Li, S.Y. Zhang, C/SiC/Si-Mo-B/glass multilayer oxidation protective coating for carbon/carbon composites, Surf. Coat. Technol. 206 (2011) 492–496. [30] X. Yang, Y.h. Zou, Q.Z. Huang, Z.A. Su, X. Chang, M.Y. Zhang, Y. Xiao, Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites, J. Cent. S. Univ. Technol. 17 (2010) 1–6.
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[31] C. Wang, J.-M. Yang, W. Hoffman, Thermal stability of refractory carbide/boride composites, Mater. Chem. Phys. 74 (2002) 272–281. [32] A. Kaiser, M. Lobert, R. Telle, Thermal stability of zircon (ZrSiO4), J. Eur. Ceram. Soc. 28 (2008) 2199–2211. [33] P. Morgan, Carbon Fibers and Their Composites, Taylor & Francis, Boca Raton, 2005. [34] J.F. Shackelford, W. Alexander, CRC Materials Science and Engineering Handbook, CRC press, Boca Raton, 2000. [35] O.S. Kwon, S.H. Hong, H. Kim, The improvement in oxidation resistance of carbon by a graded SiC/SiO2 coating, J. Eur. Ceram. Soc. 23 (2003) 3119–3124.
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