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Reactive hot pressing of SiC-ZrC composites at low temperature
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Reactive hot pressing of SiC-ZrC composites at low temperature Kun Wang a,b , Youfu Zhou a,∗ , Wentao Xu a , Ming Xiang a , Xiaoqiang Li a , Zhiguang Wang c a Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, China b School of Materials Sciences and Energy Engineering, Foshan University, Foshan, 528000, Guangdong Province, China c Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, 730000, China
a r t i c l e
i n f o
Article history: Received 26 April 2016 Received in revised form 18 August 2016 Accepted 21 August 2016 Available online xxx Keywords: Ceramic Composites Reactive hot pressing Mechanical properties
a b s t r a c t SiC-ZrC composites with relative density in excess of 99% were prepared by reactive hot pressing (RHP) of SiC and ZrH2 at 1800 ◦ C for 1 h. The reaction between SiC and ZrH2 resulted in the formation of ZrC1-x . The formation process and densification behavior during RHP process were investigated. Low temperature densification of SiC-ZrC composites is attributed to the formed nonstoichiometric ZrC1-x and the removal of SiO2 impurity on the surface of SiC particles. As reinforced phase, ZrC1-x has inhibiting effect on the abnormal grain growth of SiC, resulting in homogeneous microstructure of fine SiC grains. Adding 10 wt% ZrH2 to SiC, the formed SiC-4.62 vol% ZrC composite exhibited better mechanical properties (Vickers hardness of 27.6 ± 0.7 GPa, flexure strength of 448 ± 38 MPa, fracture toughness of 6.0± 0.3 MPa·m1/2 , respectively) than monolithic SiC ceramic. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Silicon carbide (SiC) is one of the most important ceramic materials due to its superior properties, such as low bulk density, high hardness, good high-temperature strength, high thermal conductivity, high oxidation resistance, which make it suitable for a wide range of industrial applications [1–3]. However, due to its strong covalent bond and low self-diffusion coefficient, poor sinterability and low fracture toughness of SiC ceramics limit their applications as structural ceramics [4]. In general, pressure-assisted techniques and high sintering temperature (>2000 ◦ C) are applied to obtain dense SiC ceramics by hot pressing from commercially available powders [5,6]. To improve the sinterability and mechanical properties of SiC ceramics, inclusion of second phase is one of the most common methods. ZrC ceramics have better high-temperature mechanical properties than SiC ceramics [7,8]. The thermal expansion coefficient of ZrC (6.7 × 10−6 K−1 ) is similar to that of SiC (5.12–5.8 × 10−6 K−1 ). Thus there are several researches about the preparation of ZrC-SiC composites mainly by introducing SiC into ZrC matrix. The added SiC has positive effect on improving the resistance to oxidation, thermal shock and corrosion properties [9–14]. However, as far as we know, there is no report about the reactive hot
∗ Corresponding author. E-mail address: [email protected] (Y. Zhou).
pressing preparation of SiC-ZrC composite with SiC matrix and ZrC additive. Only few researches focus on the fabrication of SiC/ZrC/C composites from polymer precursors [15]. Herein, highly dense SiC-ZrC composites were obtained by reactive hot pressing (RHP) using SiC and ZrH2 as starting materials at low temperature (1800 ◦ C). The phase composition and Rietveld refinement were investigated. The reaction process and densification behavior during the RHP were also discussed. In addition, mechanical properties of SiC-ZrC composites were compared with those of monolithic SiC ceramic.
2. Experimental procedure 2.1. Preparation of SiC-ZrC composites The starting powders are SiC (99%, 0.5–0.7 m, from Aladdin Inc., China) and ZrH2 (99.9%, from Aladdin Inc., China). SiC and different contents (5, 10 wt%) of ZrH2 were mixed with ethanol in a polyurethane jar and the corresponding samples were designated as SZ5 and SZ10, respectively. The mixed powders were ball-milled for 20 h with agate balls. The milling speed is 250 rpm and ballsto-powder ratio is 10:1. The ball-milled slurry was dried at 80 ◦ C, and then pulverized and screened through a 100-mesh sieve. Then the mixed powders were compacted in a graphite die lined with a graphite foil and coated with BN. The products were hot-pressed at 1800 ◦ C for 1 h in pure Ar atmosphere (99.99% pure). A heating rate of 10 ◦ C/min was used and a pressure of 30 MPa was applied
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from 1450 ◦ C. After holding at soaking temperatures for 60 min, the applied pressure was removed and the furnace was cooled naturally to room temperature. 2.2. Characterization Bulk density and theoretical density were evaluated by using the Archimedes method and the rule of mixtures, respectively. The phase composition of the synthesized composites was identified by X-ray diffraction (XRD) analysis with a Miniflex 600 diffractometer (Tokyo, Japan) using Cu Ka radiation. The exact O element contents of samples were characterized by an ONH836 analyzer (LECO, USA). The morphology and structures of the products were characterized by the backscattered electron images (BSE, TM3030, Hitachi). Vickers Hardness was measured on the polished surfaces of specimens by a HV-1000 Vickers hardness instrument with a load of 9.8 N with duration of 10 s. Flexure strength of the composites was measured by three-point bending method according to GB/T 6569-2006 using a universal testing machine. The indentation technique were employed for determining the fracture toughness of the samples. The dimensions of specimens for flexural strength were 3 mm × 4 mm × 36 mm. The bars were loaded with spans of 30 mm, and the crosshead speed for bending strength was 0.5 mm/min. Indentation fracture toughness values of the specimens were semi quantitatively estimated from observed corner cracks and calculated Vickers hardness using the Anstis equation [16]:
E 12 C + C − 32 1 2
KIC = 0.016
Hv
·
4
.
Where P is the indentation load (9.8N), E is the Young’s modulus, Hv is the Vickers hardness and C1 and C2 are the measured diagonal crack lengths (m) formed by the indentation. 3. Result and discussion 3.1. Phase composition and reaction process X-Ray diffraction patterns of SZ5 and SZ10 sintered at different temperatures are shown in Fig. 1. The disappearance of ZrH2 diffraction peaks in XRD patterns of both SZ5 and SZ10 sintered at 900 ◦ C implies that ZrH2 has decomposed into Zr and H2 below this temperature. It is interesting to notice that ZrO2 peaks but not Zr peaks begin to emerge at 900 ◦ C. The intensity of ZrO2 peaks increases a little bit with the increase of temperature up to 1100 ◦ C and then decrease to disappearance from 1300 ◦ C to 1600 ◦ C, especially for SZ10. To avoid the detrimental effect of O, ZrH2 is used as raw material and the purity of argon is as highly as 99.99%. So the O is probably provided by SiO2 impurity that comes from the oxidized surface of some SiC particles [17]. Finally, the phase compositions of both SZ5 and SZ10 are SiC and ZrC at 1600 ◦ C. The ZrC diffraction peaks are detected from 1300 ◦ C in SZ10, while those only can be detected at 1600 ◦ C in SZ5. In addition, the O element contents of samples were characterized by an ONH836 analyzer. The raw SZ5 powders and SZ5 sintered at 1100 ◦ C contain 1.38% and 1.689% O element respectively, while that data of SZ5 sintered at 1600 ◦ C decreases to 0.76%. According to the results of phase identification and the change of O element content, the reaction process between SiC and additive ZrH2 could be assumed as the following three reactions. Firstly, ZrH2 decomposes to Zr and H2 at 500 ◦ C–700 ◦ C, as shown in Eq. (1). Then from 890 ◦ C, the formed Zr begins to react with the SiO2 impurity which covers the surface of SiC particles to form ZrO2 , as shown in Eq. (2). Finally, with the continuous increase of temperature, ZrO2 further reacts with remain Zr and SiC to form ZrC, as shown in Eq. (3). ZrH2 → Zr + H2 ↑
Fig. 1. XRD patterns of SZ5 (a) and SZ10 (b) sintered at different temperatures.
Fig. 2. Rietveld refinement of the powder XRD pattern of SZ5 sintered at 1800 ◦ C (observed-cross, calculated-red line, difference between observed and calculatedbottom blue line, purple vertical bar-2 position of SiC, sapphire vertical bar-2 position of ZrC). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
(1)
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Table 1 Summary of Rietveld analysis results of SZ5 and SZ10 sintered at 1600 ◦ C and 1800 ◦ C. Volume fraction (Vol%) Phases SZ5 at 1600 ◦ C SiC ZrC SZ10 at 1600 ◦ C SiC ZrC SZ5 at 1800 ◦ C SiC ZrC SZ10 at 1800 ◦ C SiC ZrC
Lattice parameters a = b (Å)
c (Å)
Comments
98.27 1.73
3.0832 4.692
15.0971
Goodness of fit; 2 = 4.17
96.96 3.04
3.0832 4.690
15.0977
Goodness of fit; 2 = 3.96
97.58 2.42
3.0833 4.688
15.0969
Goodness of fit; 2 = 5.81
95.38 4.62
3.0827 4.687
15.0974
Goodness of fit; 2 = 4.77
white grains (average size about 3–5 m) distributed in SiC matrix with low Si content and high Zr content should be ZrC. The changes of relative density can also be confirmed by microstructure images. BSE images of fracture surfaces of SZ5 and SZ10 sintered at 1700 ◦ C and 1800 ◦ C are shown in Fig. 5. Although a lot of small pores could be observed in fracture surfaces of SZ5 (Fig. 5a) and SZ10 (Fig. 5b) sintered at 1700 ◦ C, the grains are homogeneously distributed with an average size less than 1 m. When the sintering temperature increases to 1800 ◦ C, both SZ5 (Fig. 5c) and SZ10 (Fig. 5d) have much finer microstructure with almost no pore, which indicates that the added Zr could improve the densification of composites. The main reason must be that the removal of SiO2 impurity on the surface of SiC particles increases the interface energy of sintered powders, according to Eqs. (2) and (3). SEM micrographs of polished surfaces of SZ5 and SZ10 sintered at 1800 ◦ C are shown in Fig. 6. The average grain size of SZ5 is about 3 m with some abnormal grain growth up to 10 m. Compared to SZ5, SZ10 exhibits nicer grain size distribution with an average Fig. 3. The displacement curves of the punch of SZ5 versus sintering time at 1700 ◦ C and 1800 ◦ C. size about 2 m and no extraordinary grain growth can be found, which demonstrates the formed ZrC from added Zr can restrain the 2SiO2 + Zr → ZrO2 + 2SiO ↑ (G = 396225-340.619T, T = 1163K = 890 ◦ C) (2) abnormal grain growth of SiC. The other reason of the improvement of sintering ability of SiCZrO2 + 2SiC + Zr → 2ZrC + 2SiO ↑ (G = 649775-367.063T, T = 1770K = 1497 ◦ C)(3) ZrC composites may be the formation of non-stoichiometric ZrC1-x In order to analyze the final phase composition and relative by the reaction between ZrC and Zr at high temperature according density of obtained ceramics at 1800 ◦ C, Rietveld analysis was introto following reaction [18]. duced to determine the mass fraction of SiC and ZrC. The result was listed as Table 1. Fig. 2 shows the measured XRD pattern and Rietveld analysis result of SZ5. The same Rietveld refinement was carried out on SZ10 and the result is similar with SZ5. The final (1-x)ZrC + xZr → ZrC1-x (4) compositions of SZ5 and SZ10 sintered at 1800 ◦ C are SiC-2.42 vol% ZrC and SiC-4.62 vol% ZrC, respectively. 3.2. Sintering and densification To show the shrinkage of SZ5 during hot-pressing processes, the displacement curves versus sintering time under different temperatures are shown as Fig. 3. The displacement curve of SZ5 sintered at 1700 ◦ C continues to rise when the temperature remain unchanged, which indicates that the densification process is not finished even at the end of soaking temperature range. But the curve of SZ5 sintered at 1800 ◦ C only rises a little at the initial phase of soaking temperature range and then keeps unchanged, which means the sample is well sintered. To observe the microstructure morphology and phase composition of obtained composites directly, backscattered electron images were employed. The BSE images of fracture surfaces for SZ10 sintered at 1800 ◦ C and the EDS line-scanning analysis are shown in Fig. 4. According to the image contrast and the EDS line-scanning analysis, the small dark particles (average size about 2 m) with high Si content and low Zr content should be SiC grains. The larger
The assumption could be confirmed by the determination of the lattice parameter of ZrC from Rietveld analysis results (Table 1). The lattice parameters of ZrC in SZ5 and SZ10 sintered at 1600 ◦ C are 4.692 and 4.690 Å, respectively, which are both much smaller than the data (4.694 Å) of nearly stoichiometric ZrC from JCPDS Card 65-0332, implying the formation of ZrC1-x . When SZ5 and SZ10 are sintered at 1800 ◦ C, the lattice parameters of ZrC1-x decrease to 4.688 Å and 4.687 Å, respectively, which are corresponding to that of ZrC0.8 (4.687 Å). The changes of carbon defect concentration in SZ5 and SZ10 could confirm the formation of non-stoichiometric ZrC1-x in reaction process. During the hot-pressing process, the existence of this non-stoichiometric ZrC1-x in SiC matrix can not only promote mass transfer through solid-state diffusion because of C vacancies, but also have positive effect on accelerating powders plastic flow [19]. So according to the rule of mixtures and ratio of experimental bulk densities and theoretical ones, the relative densities of SZ5 and SZ10 sintered at 1800 ◦ C are as high as 99.7% and 99.6%.
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Fig. 4. The BSE images of fracture surfaces for SZ10 and the EDS line-scanning analysis showing the distribution of Zr and Si elements.
Fig. 5. BSE images of SZ5 and SZ10 sintered at different temperature. (a) SZ5 at 1700 ◦ C; (b) SZ5 at 1800 ◦ C; (c) SZ10 at 1700 ◦ C; (d) SZ10 at 1800 ◦ C.
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Fig. 6. SEM micrographs of polished surfaces of SZ5 and SZ10 sintered at 1800 ◦ C.
Fig. 7. Optical micrographs of the indentation and its cracks of (a) monolithic SiC sintered at 1950 ◦ C; (b) SZ5 at 1800 ◦ C; (c) SZ10 at 1800 ◦ C.
Table 2 Mechanical properties of SZ5 and SZ10. sample
Hv (GPa)
s (MPa)
KIC (MPa·m1/2 )
SiC SZ5 SZ10
23.0 ± 1.7 25.1 ± 1.1 27.6 ± 0.7
437 ± 33 486 ± 20 448 ± 38
4.8 ± 0.3 5.5 ± 0.2 6.0 ± 0.3
3.3. Mechanical properties The mechanical properties of SZ5 and SZ10 were characterized and listed in Table 2. The hardness of SZ5 and SZ10 increases to 25.1 ± 1.1 GPa and 27.6 ± 0.7 GPa respectively due to their finer microstructure. Although the hardness of ZrC (20 GPa) [20] is not high, the hardness of SZ5 and SZ10 sintered at 1800 ◦ C are much higher than that of monolithic SiC (23.0 ± 1.7 GPa). The flexure strength of SZ5 (486 ± 20 MPa) and SZ10 (448 ± 38 MPa) are also better than that of monolithic SiC (437 ± 33 MPa). It is noteworthy that the low fracture toughness of monolithic SiC (4.8 ± 0.3 MPa·m1/2 ) has been improved. The fracture toughness of SZ5 and SZ10 are 5.5 ± 0.2 MPa·m1/2 and 6.0 ± 0.3 MPa·m1/2 , respectively.
Optical micrographs of the indentation and its cracks of different samples have been shown as Fig. 7. Fig. 7(a) corresponds to SiC ceramics sintered at 1950 ◦ C. Fig. 7(b) and (c) correspond to SZ5 and SZ10 sintered at 1800 ◦ C, respectively. It can be seen that all ceramics show clear indentations. Monolithic SiC ceramic exhibits long and straight cracks induced by the indentation. In case of SiCZrC composites, the cracks become shorter and more curved and the indentations become smaller. The improvement of mechanical properties can be ascribed to several factors. The relative densities of composites are so high above 99.6% that almost no pore exists in the SiC-ZrC composites. And the composites exhibit fine grain microstructure of SiC matrix, which can reduce the formation of microcrack during the sintering process. The grain-size distribution of the SiC matrix is narrow (1–4 m), and the average size does not exceed 3 m. Some elongated SiC grains with higher aspect ratio can be found in the composites, which are usually effective in increasing the fracture toughness of ceramics by crack deflection or crack bridging, as proved by many researchers [21–23]. And the different thermal expansion coefficient of ZrC and SiC generate residual stress around ZrC particles during cooling and this residual stress gives rise to the microcracks resulting in the fracture crack deflection
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References
Fig. 8. SEM images of the indentation crack paths of (a) SZ5 and (b) SZ10 sintered at 1800 ◦ C.
[24]. Fig. 8(a) and (b) showed SEM images of the indentation crack paths of SZ5 and SZ10, respectively. Crack deflection and crack bridging were observed in both composites of SZ5 and SZ10, which increased resistance against crack propagation in the samples and consumed more energy for the separation of fractured surface [25]. The fracture surfaces of the SiC/ZrC composites are both rough and smooth, showing a mixture of intergranular and transgranular fracture mode, which indicates that the fracture mode of SiC changes from transgranular fracture to both intergranular and transgranular fracture [26]. 4. Conclusion SiC-ZrC composites with high density (excess 99%) were prepared by reactive hot pressing (RHP) of commercial SiC and ZrH2 at lower temperature (1800 ◦ C) than routine procedure (above 2000 ◦ C). The addition of ZrH2 enhances the sinterability of SiC ceramics and increases the corresponding mechanical properties. The new-formed ZrC grains have inhibiting effect on the grain growth of SiC, resulting in fine grain size of SiC matrix. Therefore, the composite of SZ10 exhibits better mechanical properties (Vickers hardness of 27.6 ± 0.7 GPa, flexure strength of 448 ± 38 MPa, fracture toughness of 6.0 ± 0.3 MPa·m1/2 , respectively) than monolithic SiC ceramics. This large promotion of fracture toughness could cover the shortage of brittleness of SiC, which is quite meaningful to the wide applications of SiC-matrix ceramics.
[1] M. Herrmann, K. Sempf, H. Wendrock, M. Schneider, K. Kremmer, A. Michaelis, Electrochemical corrosion of silicon carbide ceramics in sodium hydroxide, J. Eur. Ceram. Soc. 34 (2014) 1687–1693. [2] N. JS, Very high pressure hot pressing of silicon carbide, Am. Ceram. Soc. Bull. 52 (1973) 170–174. [3] D. SJ, Ceramic heat exchangers, Am. Ceram. Soc. Bull. 67 (1988) 388–391. [4] R. J, C. Greskovich, Sintering of covalent solids, J. Am. Ceram. Soc. 59 (1976) 336–343. [5] Y. Zhou, H. Tanaka, S. Otani, Y. Bando, Low-temperature pressureless sintering of alpha-SiC with Al4 C3 -B4 C-C additions, J. Am. Ceram. Soc. 82 (1999) 1959–1964. [6] K.-Y. Lim, Y.-W. Kim, K. Joo Kim, Electrical properties of SiC ceramics sintered with 0.5 wt% AlN–RE2 O3 (RE = Y, Nd, Lu), Ceram. Int. 40 (2014) 8885–8890. [7] L. Rangaraj, C. Divakar, V. Jayaram, Reactive hot pressing of ZrB2 –ZrCx ultra-high temperature ceramic composites with the addition of SiC particulate, J. Eur. Ceram. Soc. 30 (2010) 3263–3266. [8] P. Barnier, C. Brodhag, F. Thevenot, Hot-pressing dinetics of zirconium carbide, J. Mater. Sci. 21 (1986) 2547–2552. [9] X.-G. Wang, G.-J. Zhang, J.-X. Xue, Y. Tang, X. Huang, C.-M. Xu, P.-L. Wang, G. Hilmas, Reactive hot pressing of ZrC-SiC ceramics at low temperature, J. Am. Ceram. Soc. 96 (2013) 32–36. [10] D. Pizon, R. Lucas, S. Foucaud, A. Maître, ZrC-SiC materials from the polymer-derived ceramics route, Adv. Eng. Mater. 13 (2011) 599–603. [11] L. Zhao, D. Jia, X. Duan, Z. Yang, Y. Zhou, Low temperature sintering of ZrC–SiC composite, J. Alloys Compd. 509 (2011) 9816–9820. ´ S. Nenadovic, ´ M. Nenadovic, ´ D. Gautam, T. Volkov-Husovic, ´ A. [12] L. Kljajevic, ´ Spark plasma sintering of ZrC–SiC ceramics with Deveˇcerski, B. Matovic, LiYO2 additive, Ceram. Int. 39 (2013) 5467–5476. [13] D. Pizon, L. Charpentier, R. Lucas, S. Foucaud, A. Maître, M. Balat-Pichelin, Oxidation behavior of spark plasma sintered ZrC–SiC composites obtained from the polymer-derived ceramics route, Ceram. Int. 40 (2014) 5025–5031. [14] X.-F. Wang, J.-C. Liu, F. Hou, J.-D. Hu, X. Sun, Y.-C. Zhou, R. Koc, Synthesis of ZrC-SiC powders from hybrid liquid precursors with Improved oxidation resistance, J. Am. Ceram. Soc. 98 (2015) 197–204. [15] M. Wang, C. Huang, Z. Wang, Polyzirconosilane preceramic resin as single source precursor of SiC?ZrC ceramics, J. Inorg. Organomet Polymers 26 (2015) 24–31. [16] G.R. Anstis, P. Chantikul, B.R. Lawn, D.B. Marshall, A critical evaluation of indentation techniques for measuring fracture toughness: I, direct crack measurements, J. Am. Ceram. Soc. 64 (1981) 533–538. [17] W.W. Wu, G.J. Zhang, Y.M. Kan, P.L. Wang, Reactive hot pressing of ZrB2 -SiC-ZrC composites at 1600◦ C, J. Am. Ceram. Soc. 91 (2008) 2501–2508. [18] X.G. Wang, W.M. Guo, Y.M. Kan, G.J. Zhang, P.L. Wang, Densification behavior and properties of hot-pressed ZrC ceramics with Zr and graphite additives, J. Eur. Ceram. Soc. 31 (2011) 1103–1111. [19] R.S.-F.K. Bhanumurthy, Interface reactions between SiC/Zr and development of zirconium base composites by in-situ solid state reactions, Scripta Mater. 45 (2001) 547–553. [20] D. Sciti, S. Guicciardi, M. Nygren, Spark plasma sintering and mechanical behaviour of zrC-Based composites, Scripta Mater. 59 (2008) 638–641. [21] C.J. Gilbert, J.J. Cao, W.J. MoberlyChan, L.C. De Jonghe, R.O. Ritchie, Cyclic fatigue and resistance-curve behavior of an in situ toughened silicon carbide with Al-B-C additions, Acta Metall. Mater. 44 (1996) 3199–3214. [22] Y.W. Kim, M. Mitomo, H. Hideki, Microstructural development of silicon carbide containing large seed grains, J. Am. Ceram. Soc. 80 (1997) 99–105. [23] P. Padture Nitin, In situ-toughened silicon carbide, J. Am. Ceram. Soc. 77 (1994) 519–523. [24] X.G. Wang, W.M. Guo, Y.M. Kan, G.J. Zhang, Hot-pressed ZrB2 ceramics with composite additives of Zr and B4 C, Adv. Eng. Mater. 12 (2010) 893–898. [25] H.L. Wang, S.-H. Lee, L. Feng, The processing and properties of (Zr, Hf)B2 –SiC nanostructured composites, J. Am. Ceram Soc. 34 (2014) 4105–4109. [26] C.C.Y.Q. Tan, F.Z. Li, H.B. Zhang, G.J. Zhang, S.M. Peng, Enhancement of sinterability and mechanical properties of B4 C ceramics using Ti3 AlC2 as a sintering aid, RSC Adv. 5 (2015) 76309–76314.
Acknowledgements The authors are grateful for the grants of CAS Priority Research program (XDA03010301), State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (KF201517) and Natural Science Foundation of Fujian Province (2014H0055).
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Short communication
Reactive hot pressing of SiC-ZrC composites at low temperature Kun Wang a,b , Youfu Zhou a,∗ , Wentao Xu a , Ming Xiang a , Xiaoqiang Li a , Zhiguang Wang c a Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, China b School of Materials Sciences and Energy Engineering, Foshan University, Foshan, 528000, Guangdong Province, China c Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, 730000, China
a r t i c l e
i n f o
Article history: Received 26 April 2016 Received in revised form 18 August 2016 Accepted 21 August 2016 Available online xxx Keywords: Ceramic Composites Reactive hot pressing Mechanical properties
a b s t r a c t SiC-ZrC composites with relative density in excess of 99% were prepared by reactive hot pressing (RHP) of SiC and ZrH2 at 1800 ◦ C for 1 h. The reaction between SiC and ZrH2 resulted in the formation of ZrC1-x . The formation process and densification behavior during RHP process were investigated. Low temperature densification of SiC-ZrC composites is attributed to the formed nonstoichiometric ZrC1-x and the removal of SiO2 impurity on the surface of SiC particles. As reinforced phase, ZrC1-x has inhibiting effect on the abnormal grain growth of SiC, resulting in homogeneous microstructure of fine SiC grains. Adding 10 wt% ZrH2 to SiC, the formed SiC-4.62 vol% ZrC composite exhibited better mechanical properties (Vickers hardness of 27.6 ± 0.7 GPa, flexure strength of 448 ± 38 MPa, fracture toughness of 6.0± 0.3 MPa·m1/2 , respectively) than monolithic SiC ceramic. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Silicon carbide (SiC) is one of the most important ceramic materials due to its superior properties, such as low bulk density, high hardness, good high-temperature strength, high thermal conductivity, high oxidation resistance, which make it suitable for a wide range of industrial applications [1–3]. However, due to its strong covalent bond and low self-diffusion coefficient, poor sinterability and low fracture toughness of SiC ceramics limit their applications as structural ceramics [4]. In general, pressure-assisted techniques and high sintering temperature (>2000 ◦ C) are applied to obtain dense SiC ceramics by hot pressing from commercially available powders [5,6]. To improve the sinterability and mechanical properties of SiC ceramics, inclusion of second phase is one of the most common methods. ZrC ceramics have better high-temperature mechanical properties than SiC ceramics [7,8]. The thermal expansion coefficient of ZrC (6.7 × 10−6 K−1 ) is similar to that of SiC (5.12–5.8 × 10−6 K−1 ). Thus there are several researches about the preparation of ZrC-SiC composites mainly by introducing SiC into ZrC matrix. The added SiC has positive effect on improving the resistance to oxidation, thermal shock and corrosion properties [9–14]. However, as far as we know, there is no report about the reactive hot
∗ Corresponding author. E-mail address: [email protected] (Y. Zhou).
pressing preparation of SiC-ZrC composite with SiC matrix and ZrC additive. Only few researches focus on the fabrication of SiC/ZrC/C composites from polymer precursors [15]. Herein, highly dense SiC-ZrC composites were obtained by reactive hot pressing (RHP) using SiC and ZrH2 as starting materials at low temperature (1800 ◦ C). The phase composition and Rietveld refinement were investigated. The reaction process and densification behavior during the RHP were also discussed. In addition, mechanical properties of SiC-ZrC composites were compared with those of monolithic SiC ceramic.
2. Experimental procedure 2.1. Preparation of SiC-ZrC composites The starting powders are SiC (99%, 0.5–0.7 m, from Aladdin Inc., China) and ZrH2 (99.9%, from Aladdin Inc., China). SiC and different contents (5, 10 wt%) of ZrH2 were mixed with ethanol in a polyurethane jar and the corresponding samples were designated as SZ5 and SZ10, respectively. The mixed powders were ball-milled for 20 h with agate balls. The milling speed is 250 rpm and ballsto-powder ratio is 10:1. The ball-milled slurry was dried at 80 ◦ C, and then pulverized and screened through a 100-mesh sieve. Then the mixed powders were compacted in a graphite die lined with a graphite foil and coated with BN. The products were hot-pressed at 1800 ◦ C for 1 h in pure Ar atmosphere (99.99% pure). A heating rate of 10 ◦ C/min was used and a pressure of 30 MPa was applied
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Please cite this article in press as: K. Wang, et al., Reactive hot pressing of SiC-ZrC composites at low temperature, J Eur Ceram Soc (2016), http://dx.doi.org/10.1016/j.jeurceramsoc.2016.08.027
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from 1450 ◦ C. After holding at soaking temperatures for 60 min, the applied pressure was removed and the furnace was cooled naturally to room temperature. 2.2. Characterization Bulk density and theoretical density were evaluated by using the Archimedes method and the rule of mixtures, respectively. The phase composition of the synthesized composites was identified by X-ray diffraction (XRD) analysis with a Miniflex 600 diffractometer (Tokyo, Japan) using Cu Ka radiation. The exact O element contents of samples were characterized by an ONH836 analyzer (LECO, USA). The morphology and structures of the products were characterized by the backscattered electron images (BSE, TM3030, Hitachi). Vickers Hardness was measured on the polished surfaces of specimens by a HV-1000 Vickers hardness instrument with a load of 9.8 N with duration of 10 s. Flexure strength of the composites was measured by three-point bending method according to GB/T 6569-2006 using a universal testing machine. The indentation technique were employed for determining the fracture toughness of the samples. The dimensions of specimens for flexural strength were 3 mm × 4 mm × 36 mm. The bars were loaded with spans of 30 mm, and the crosshead speed for bending strength was 0.5 mm/min. Indentation fracture toughness values of the specimens were semi quantitatively estimated from observed corner cracks and calculated Vickers hardness using the Anstis equation [16]:
E 12 C + C − 32 1 2
KIC = 0.016
Hv
·
4
.
Where P is the indentation load (9.8N), E is the Young’s modulus, Hv is the Vickers hardness and C1 and C2 are the measured diagonal crack lengths (m) formed by the indentation. 3. Result and discussion 3.1. Phase composition and reaction process X-Ray diffraction patterns of SZ5 and SZ10 sintered at different temperatures are shown in Fig. 1. The disappearance of ZrH2 diffraction peaks in XRD patterns of both SZ5 and SZ10 sintered at 900 ◦ C implies that ZrH2 has decomposed into Zr and H2 below this temperature. It is interesting to notice that ZrO2 peaks but not Zr peaks begin to emerge at 900 ◦ C. The intensity of ZrO2 peaks increases a little bit with the increase of temperature up to 1100 ◦ C and then decrease to disappearance from 1300 ◦ C to 1600 ◦ C, especially for SZ10. To avoid the detrimental effect of O, ZrH2 is used as raw material and the purity of argon is as highly as 99.99%. So the O is probably provided by SiO2 impurity that comes from the oxidized surface of some SiC particles [17]. Finally, the phase compositions of both SZ5 and SZ10 are SiC and ZrC at 1600 ◦ C. The ZrC diffraction peaks are detected from 1300 ◦ C in SZ10, while those only can be detected at 1600 ◦ C in SZ5. In addition, the O element contents of samples were characterized by an ONH836 analyzer. The raw SZ5 powders and SZ5 sintered at 1100 ◦ C contain 1.38% and 1.689% O element respectively, while that data of SZ5 sintered at 1600 ◦ C decreases to 0.76%. According to the results of phase identification and the change of O element content, the reaction process between SiC and additive ZrH2 could be assumed as the following three reactions. Firstly, ZrH2 decomposes to Zr and H2 at 500 ◦ C–700 ◦ C, as shown in Eq. (1). Then from 890 ◦ C, the formed Zr begins to react with the SiO2 impurity which covers the surface of SiC particles to form ZrO2 , as shown in Eq. (2). Finally, with the continuous increase of temperature, ZrO2 further reacts with remain Zr and SiC to form ZrC, as shown in Eq. (3). ZrH2 → Zr + H2 ↑
Fig. 1. XRD patterns of SZ5 (a) and SZ10 (b) sintered at different temperatures.
Fig. 2. Rietveld refinement of the powder XRD pattern of SZ5 sintered at 1800 ◦ C (observed-cross, calculated-red line, difference between observed and calculatedbottom blue line, purple vertical bar-2 position of SiC, sapphire vertical bar-2 position of ZrC). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
(1)
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Table 1 Summary of Rietveld analysis results of SZ5 and SZ10 sintered at 1600 ◦ C and 1800 ◦ C. Volume fraction (Vol%) Phases SZ5 at 1600 ◦ C SiC ZrC SZ10 at 1600 ◦ C SiC ZrC SZ5 at 1800 ◦ C SiC ZrC SZ10 at 1800 ◦ C SiC ZrC
Lattice parameters a = b (Å)
c (Å)
Comments
98.27 1.73
3.0832 4.692
15.0971
Goodness of fit; 2 = 4.17
96.96 3.04
3.0832 4.690
15.0977
Goodness of fit; 2 = 3.96
97.58 2.42
3.0833 4.688
15.0969
Goodness of fit; 2 = 5.81
95.38 4.62
3.0827 4.687
15.0974
Goodness of fit; 2 = 4.77
white grains (average size about 3–5 m) distributed in SiC matrix with low Si content and high Zr content should be ZrC. The changes of relative density can also be confirmed by microstructure images. BSE images of fracture surfaces of SZ5 and SZ10 sintered at 1700 ◦ C and 1800 ◦ C are shown in Fig. 5. Although a lot of small pores could be observed in fracture surfaces of SZ5 (Fig. 5a) and SZ10 (Fig. 5b) sintered at 1700 ◦ C, the grains are homogeneously distributed with an average size less than 1 m. When the sintering temperature increases to 1800 ◦ C, both SZ5 (Fig. 5c) and SZ10 (Fig. 5d) have much finer microstructure with almost no pore, which indicates that the added Zr could improve the densification of composites. The main reason must be that the removal of SiO2 impurity on the surface of SiC particles increases the interface energy of sintered powders, according to Eqs. (2) and (3). SEM micrographs of polished surfaces of SZ5 and SZ10 sintered at 1800 ◦ C are shown in Fig. 6. The average grain size of SZ5 is about 3 m with some abnormal grain growth up to 10 m. Compared to SZ5, SZ10 exhibits nicer grain size distribution with an average Fig. 3. The displacement curves of the punch of SZ5 versus sintering time at 1700 ◦ C and 1800 ◦ C. size about 2 m and no extraordinary grain growth can be found, which demonstrates the formed ZrC from added Zr can restrain the 2SiO2 + Zr → ZrO2 + 2SiO ↑ (G = 396225-340.619T, T = 1163K = 890 ◦ C) (2) abnormal grain growth of SiC. The other reason of the improvement of sintering ability of SiCZrO2 + 2SiC + Zr → 2ZrC + 2SiO ↑ (G = 649775-367.063T, T = 1770K = 1497 ◦ C)(3) ZrC composites may be the formation of non-stoichiometric ZrC1-x In order to analyze the final phase composition and relative by the reaction between ZrC and Zr at high temperature according density of obtained ceramics at 1800 ◦ C, Rietveld analysis was introto following reaction [18]. duced to determine the mass fraction of SiC and ZrC. The result was listed as Table 1. Fig. 2 shows the measured XRD pattern and Rietveld analysis result of SZ5. The same Rietveld refinement was carried out on SZ10 and the result is similar with SZ5. The final (1-x)ZrC + xZr → ZrC1-x (4) compositions of SZ5 and SZ10 sintered at 1800 ◦ C are SiC-2.42 vol% ZrC and SiC-4.62 vol% ZrC, respectively. 3.2. Sintering and densification To show the shrinkage of SZ5 during hot-pressing processes, the displacement curves versus sintering time under different temperatures are shown as Fig. 3. The displacement curve of SZ5 sintered at 1700 ◦ C continues to rise when the temperature remain unchanged, which indicates that the densification process is not finished even at the end of soaking temperature range. But the curve of SZ5 sintered at 1800 ◦ C only rises a little at the initial phase of soaking temperature range and then keeps unchanged, which means the sample is well sintered. To observe the microstructure morphology and phase composition of obtained composites directly, backscattered electron images were employed. The BSE images of fracture surfaces for SZ10 sintered at 1800 ◦ C and the EDS line-scanning analysis are shown in Fig. 4. According to the image contrast and the EDS line-scanning analysis, the small dark particles (average size about 2 m) with high Si content and low Zr content should be SiC grains. The larger
The assumption could be confirmed by the determination of the lattice parameter of ZrC from Rietveld analysis results (Table 1). The lattice parameters of ZrC in SZ5 and SZ10 sintered at 1600 ◦ C are 4.692 and 4.690 Å, respectively, which are both much smaller than the data (4.694 Å) of nearly stoichiometric ZrC from JCPDS Card 65-0332, implying the formation of ZrC1-x . When SZ5 and SZ10 are sintered at 1800 ◦ C, the lattice parameters of ZrC1-x decrease to 4.688 Å and 4.687 Å, respectively, which are corresponding to that of ZrC0.8 (4.687 Å). The changes of carbon defect concentration in SZ5 and SZ10 could confirm the formation of non-stoichiometric ZrC1-x in reaction process. During the hot-pressing process, the existence of this non-stoichiometric ZrC1-x in SiC matrix can not only promote mass transfer through solid-state diffusion because of C vacancies, but also have positive effect on accelerating powders plastic flow [19]. So according to the rule of mixtures and ratio of experimental bulk densities and theoretical ones, the relative densities of SZ5 and SZ10 sintered at 1800 ◦ C are as high as 99.7% and 99.6%.
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Fig. 4. The BSE images of fracture surfaces for SZ10 and the EDS line-scanning analysis showing the distribution of Zr and Si elements.
Fig. 5. BSE images of SZ5 and SZ10 sintered at different temperature. (a) SZ5 at 1700 ◦ C; (b) SZ5 at 1800 ◦ C; (c) SZ10 at 1700 ◦ C; (d) SZ10 at 1800 ◦ C.
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Fig. 6. SEM micrographs of polished surfaces of SZ5 and SZ10 sintered at 1800 ◦ C.
Fig. 7. Optical micrographs of the indentation and its cracks of (a) monolithic SiC sintered at 1950 ◦ C; (b) SZ5 at 1800 ◦ C; (c) SZ10 at 1800 ◦ C.
Table 2 Mechanical properties of SZ5 and SZ10. sample
Hv (GPa)
s (MPa)
KIC (MPa·m1/2 )
SiC SZ5 SZ10
23.0 ± 1.7 25.1 ± 1.1 27.6 ± 0.7
437 ± 33 486 ± 20 448 ± 38
4.8 ± 0.3 5.5 ± 0.2 6.0 ± 0.3
3.3. Mechanical properties The mechanical properties of SZ5 and SZ10 were characterized and listed in Table 2. The hardness of SZ5 and SZ10 increases to 25.1 ± 1.1 GPa and 27.6 ± 0.7 GPa respectively due to their finer microstructure. Although the hardness of ZrC (20 GPa) [20] is not high, the hardness of SZ5 and SZ10 sintered at 1800 ◦ C are much higher than that of monolithic SiC (23.0 ± 1.7 GPa). The flexure strength of SZ5 (486 ± 20 MPa) and SZ10 (448 ± 38 MPa) are also better than that of monolithic SiC (437 ± 33 MPa). It is noteworthy that the low fracture toughness of monolithic SiC (4.8 ± 0.3 MPa·m1/2 ) has been improved. The fracture toughness of SZ5 and SZ10 are 5.5 ± 0.2 MPa·m1/2 and 6.0 ± 0.3 MPa·m1/2 , respectively.
Optical micrographs of the indentation and its cracks of different samples have been shown as Fig. 7. Fig. 7(a) corresponds to SiC ceramics sintered at 1950 ◦ C. Fig. 7(b) and (c) correspond to SZ5 and SZ10 sintered at 1800 ◦ C, respectively. It can be seen that all ceramics show clear indentations. Monolithic SiC ceramic exhibits long and straight cracks induced by the indentation. In case of SiCZrC composites, the cracks become shorter and more curved and the indentations become smaller. The improvement of mechanical properties can be ascribed to several factors. The relative densities of composites are so high above 99.6% that almost no pore exists in the SiC-ZrC composites. And the composites exhibit fine grain microstructure of SiC matrix, which can reduce the formation of microcrack during the sintering process. The grain-size distribution of the SiC matrix is narrow (1–4 m), and the average size does not exceed 3 m. Some elongated SiC grains with higher aspect ratio can be found in the composites, which are usually effective in increasing the fracture toughness of ceramics by crack deflection or crack bridging, as proved by many researchers [21–23]. And the different thermal expansion coefficient of ZrC and SiC generate residual stress around ZrC particles during cooling and this residual stress gives rise to the microcracks resulting in the fracture crack deflection
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References
Fig. 8. SEM images of the indentation crack paths of (a) SZ5 and (b) SZ10 sintered at 1800 ◦ C.
[24]. Fig. 8(a) and (b) showed SEM images of the indentation crack paths of SZ5 and SZ10, respectively. Crack deflection and crack bridging were observed in both composites of SZ5 and SZ10, which increased resistance against crack propagation in the samples and consumed more energy for the separation of fractured surface [25]. The fracture surfaces of the SiC/ZrC composites are both rough and smooth, showing a mixture of intergranular and transgranular fracture mode, which indicates that the fracture mode of SiC changes from transgranular fracture to both intergranular and transgranular fracture [26]. 4. Conclusion SiC-ZrC composites with high density (excess 99%) were prepared by reactive hot pressing (RHP) of commercial SiC and ZrH2 at lower temperature (1800 ◦ C) than routine procedure (above 2000 ◦ C). The addition of ZrH2 enhances the sinterability of SiC ceramics and increases the corresponding mechanical properties. The new-formed ZrC grains have inhibiting effect on the grain growth of SiC, resulting in fine grain size of SiC matrix. Therefore, the composite of SZ10 exhibits better mechanical properties (Vickers hardness of 27.6 ± 0.7 GPa, flexure strength of 448 ± 38 MPa, fracture toughness of 6.0 ± 0.3 MPa·m1/2 , respectively) than monolithic SiC ceramics. This large promotion of fracture toughness could cover the shortage of brittleness of SiC, which is quite meaningful to the wide applications of SiC-matrix ceramics.
[1] M. Herrmann, K. Sempf, H. Wendrock, M. Schneider, K. Kremmer, A. Michaelis, Electrochemical corrosion of silicon carbide ceramics in sodium hydroxide, J. Eur. Ceram. Soc. 34 (2014) 1687–1693. [2] N. JS, Very high pressure hot pressing of silicon carbide, Am. Ceram. Soc. Bull. 52 (1973) 170–174. [3] D. SJ, Ceramic heat exchangers, Am. Ceram. Soc. Bull. 67 (1988) 388–391. [4] R. J, C. Greskovich, Sintering of covalent solids, J. Am. Ceram. Soc. 59 (1976) 336–343. [5] Y. Zhou, H. Tanaka, S. Otani, Y. Bando, Low-temperature pressureless sintering of alpha-SiC with Al4 C3 -B4 C-C additions, J. Am. Ceram. Soc. 82 (1999) 1959–1964. [6] K.-Y. Lim, Y.-W. Kim, K. Joo Kim, Electrical properties of SiC ceramics sintered with 0.5 wt% AlN–RE2 O3 (RE = Y, Nd, Lu), Ceram. Int. 40 (2014) 8885–8890. [7] L. Rangaraj, C. Divakar, V. Jayaram, Reactive hot pressing of ZrB2 –ZrCx ultra-high temperature ceramic composites with the addition of SiC particulate, J. Eur. Ceram. Soc. 30 (2010) 3263–3266. [8] P. Barnier, C. Brodhag, F. Thevenot, Hot-pressing dinetics of zirconium carbide, J. Mater. Sci. 21 (1986) 2547–2552. [9] X.-G. Wang, G.-J. Zhang, J.-X. Xue, Y. Tang, X. Huang, C.-M. Xu, P.-L. Wang, G. Hilmas, Reactive hot pressing of ZrC-SiC ceramics at low temperature, J. Am. Ceram. Soc. 96 (2013) 32–36. [10] D. Pizon, R. Lucas, S. Foucaud, A. Maître, ZrC-SiC materials from the polymer-derived ceramics route, Adv. Eng. Mater. 13 (2011) 599–603. [11] L. Zhao, D. Jia, X. Duan, Z. Yang, Y. Zhou, Low temperature sintering of ZrC–SiC composite, J. Alloys Compd. 509 (2011) 9816–9820. ´ S. Nenadovic, ´ M. Nenadovic, ´ D. Gautam, T. Volkov-Husovic, ´ A. [12] L. Kljajevic, ´ Spark plasma sintering of ZrC–SiC ceramics with Deveˇcerski, B. Matovic, LiYO2 additive, Ceram. Int. 39 (2013) 5467–5476. [13] D. Pizon, L. Charpentier, R. Lucas, S. Foucaud, A. Maître, M. Balat-Pichelin, Oxidation behavior of spark plasma sintered ZrC–SiC composites obtained from the polymer-derived ceramics route, Ceram. Int. 40 (2014) 5025–5031. [14] X.-F. Wang, J.-C. Liu, F. Hou, J.-D. Hu, X. Sun, Y.-C. Zhou, R. Koc, Synthesis of ZrC-SiC powders from hybrid liquid precursors with Improved oxidation resistance, J. Am. Ceram. Soc. 98 (2015) 197–204. [15] M. Wang, C. Huang, Z. Wang, Polyzirconosilane preceramic resin as single source precursor of SiC?ZrC ceramics, J. Inorg. Organomet Polymers 26 (2015) 24–31. [16] G.R. Anstis, P. Chantikul, B.R. Lawn, D.B. Marshall, A critical evaluation of indentation techniques for measuring fracture toughness: I, direct crack measurements, J. Am. Ceram. Soc. 64 (1981) 533–538. [17] W.W. Wu, G.J. Zhang, Y.M. Kan, P.L. Wang, Reactive hot pressing of ZrB2 -SiC-ZrC composites at 1600◦ C, J. Am. Ceram. Soc. 91 (2008) 2501–2508. [18] X.G. Wang, W.M. Guo, Y.M. Kan, G.J. Zhang, P.L. Wang, Densification behavior and properties of hot-pressed ZrC ceramics with Zr and graphite additives, J. Eur. Ceram. Soc. 31 (2011) 1103–1111. [19] R.S.-F.K. Bhanumurthy, Interface reactions between SiC/Zr and development of zirconium base composites by in-situ solid state reactions, Scripta Mater. 45 (2001) 547–553. [20] D. Sciti, S. Guicciardi, M. Nygren, Spark plasma sintering and mechanical behaviour of zrC-Based composites, Scripta Mater. 59 (2008) 638–641. [21] C.J. Gilbert, J.J. Cao, W.J. MoberlyChan, L.C. De Jonghe, R.O. Ritchie, Cyclic fatigue and resistance-curve behavior of an in situ toughened silicon carbide with Al-B-C additions, Acta Metall. Mater. 44 (1996) 3199–3214. [22] Y.W. Kim, M. Mitomo, H. Hideki, Microstructural development of silicon carbide containing large seed grains, J. Am. Ceram. Soc. 80 (1997) 99–105. [23] P. Padture Nitin, In situ-toughened silicon carbide, J. Am. Ceram. Soc. 77 (1994) 519–523. [24] X.G. Wang, W.M. Guo, Y.M. Kan, G.J. Zhang, Hot-pressed ZrB2 ceramics with composite additives of Zr and B4 C, Adv. Eng. Mater. 12 (2010) 893–898. [25] H.L. Wang, S.-H. Lee, L. Feng, The processing and properties of (Zr, Hf)B2 –SiC nanostructured composites, J. Am. Ceram Soc. 34 (2014) 4105–4109. [26] C.C.Y.Q. Tan, F.Z. Li, H.B. Zhang, G.J. Zhang, S.M. Peng, Enhancement of sinterability and mechanical properties of B4 C ceramics using Ti3 AlC2 as a sintering aid, RSC Adv. 5 (2015) 76309–76314.
Acknowledgements The authors are grateful for the grants of CAS Priority Research program (XDA03010301), State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (KF201517) and Natural Science Foundation of Fujian Province (2014H0055).
Please cite this article in press as: K. Wang, et al., Reactive hot pressing of SiC-ZrC composites at low temperature, J Eur Ceram Soc (2016), http://dx.doi.org/10.1016/j.jeurceramsoc.2016.08.027