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Seamless joining of silicon carbide ceramics through an sacrificial interlayer of Dy3Si2C2
Journal of the European Ceramic Society 39 (2019) 5457–5462
Contents lists available at ScienceDirect
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Short communication
Seamless joining of silicon carbide ceramics through an sacrificial interlayer of Dy3Si2C2
T
⁎
Peng Wana,b,1, Mian Lib,1, Kai Xub, Haibo Wuc, Keke Changb, Xiaobing Zhoub, Xiangdong Dinga, , ⁎ Zhengren Huangb, Hongxiang Zonga, Qing Huangb, a
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xian, Shaanxi, 710049, China Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang, 315201, China c State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Joining Silicon carbide Ternary carbide Molten salt
A ternary carbide Dy3Si2C2 coating was fabricated on the surface of SiC through a molten salt technique. Using the Dy3Si2C2 coating as the joining interlayer, seamless joining of SiC ceramic was achieved at temperature as low as 1500 °C. Phase diagram calculation indicates that seamless joining was achieved by the formation of liquid phase at the interface between Dy3Si2C2 and SiC, which was squeezed out under pressure and continuously consumed by the joining interlayer. This work implies the great potential of the family of ternary rareearth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the sacrificial interlayer for high-quality SiC joining.
1. Introduction Silicon carbide (SiC) has the properties of low density, high strength, good high temperature stability, good corrosion resistance, and low neutron-induced activation, [1–3], which makes it a promising candidate for aerospace structural material, electronics device, and nuclear structural material. The strong Si-C covalent bond endows SiC high hardness, intrinsic brittleness and low self-diffusivity coefficient, which makes it difficult to be formed and manufactured in near netshape. Therefore, joining is considered to be an effective way to obtain large-sized and complex-shaped SiC components [4]. In the last decades, direct bonding and indirect bonding method have been developed for SiC joining. Direct bonding is achieved by inter-diffusion between SiC couples, which requires high joining temperature (∼1900 °C) and high pressure [5]. Indirect joining is achieved by adding a joining interlayer between SiC couples that can promote atom diffusion and decrease the joining temperature. Therefore, choosing suitable interlayer materials is critically important for highquality SiC joining [6]. So far, variety of interlayer materials have been explored for SiC joining, such as full metallic interlayer (Ti, Mo, Ni, AlTi, and Ag-Cu [7–11]), metal-ceramic hybrid interlayer (Al-TiC, Ti-B4CSi, and Ti-BN-Al [4,12]), glass-ceramic interlayer (Y2O3-Al2O3-SiO2, CaO-MgO-Al2O3-SiO2 [13,14]), and MAX phase interlayer (Ti3SiC2
[15]). Most of these interlayers retained in the final SiC joint, which is harmful to the stability of SiC joint when exposed in extreme environments, e.g. high temperature, severe oxidation/corrosion and irradiation environment. Moreover, the thermal mismatch between SiC and interlayer results in residual stress, which decreases the stability of the joint. Therefore, in the last years, researchers show great interests in exploring suitable joining strategy to achieve seamless SiC joining. In our previous work, we have developed a molten salts technique that can fabricate metal carbides (e.g. Ti3SiC2 and Y3Si2C2) coating on SiC fibers and SiC powders [16,17]. By using Y3Si2C2 coated SiC powders as the starting materials, fully dense SiC ceramic was obtained through spark plasma sintering (SPS) at 1700 °C [17]. The densification of SiC ceramic was promoted by the formation of eutectic phase between Y3Si2C2 and SiC, which can accelerate the atom diffusion and grain growth. Notably, the as-formed liquid phase was extruded during the sintering process, thus the as-obtained SiC ceramics contains no residual Y3Si2C2 but a little by-product Y2O3. Note that Y3Si2C2 have a family of ternary rare-earth carbides with similar structure, i.e. Re3Si2C2 (Re = Y, La-Nd) [18]. The family of Re3Si2C2 are expected to have similar properties with Y3Si2C2, which may be used to promote the sintering and seamless joining of SiC. In the present work, a Dy3Si2C2 coating was fabricated on the surface of SiC through the molten salt technique. By using the Dy3Si2C2 coating as the joining interlayer,
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Corresponding authors. E-mail addresses: [email protected] (X. Ding), [email protected] (Q. Huang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jeurceramsoc.2019.09.002 Received 31 July 2019; Received in revised form 30 August 2019; Accepted 1 September 2019 Available online 03 September 2019 0955-2219/ © 2019 Elsevier Ltd. All rights reserved.
Journal of the European Ceramic Society 39 (2019) 5457–5462
P. Wan, et al.
Fig. 1. Schematic diagram showing the Dy3Si2C2 coating fabricating process.
Fig. 2. Characterization of the Dy3Si2C2 coating: (a) XRD patterns of coating and substrate; (b), (c) TEM image showing the cross-section of the coating and corresponding EDS map showing the element distribution.
Research Institute, Hunan, China; purity: 99.5%, mean particle size: 75 μm). The schematic diagram of the fabricating process was shown in Fig. 1. First, the SiC block was placed in an alumina crucible. After that, Dy powder and NaCl salt with the mass ratio of 1:10 was mixed thoroughly using a mortar under the protection of nitrogen in a glovebox. Then the NaCl/Dy mixture was placed into alumina crucible and covered the SiC block. The alumina crucible was loaded into a tube furnace and heat treated at 900 °C for 60 min under the protection of Ar gas. Then the tube furnace was naturally cooled to the room temperature. After that, the product was washed by deionized water for five times to remove the residual NaCl and Dy. Finally, the SiC block with Dy3Si2C2 coating was obtained. Two as-obtained Dy3Si2C2 coated SiC blocks were put into a graphite die to perform the joining. The graphite die was then loaded into a SPS furnace (HP D25/1, FCT Systeme GmbH, Rauenstein, Germany) and heated to target temperature (1300 °C–1600 °C) with a rate of
seamless joining of SiC ceramic was achieved at the temperature as low as 1500 °C through an electric current field-assisted sintering technology (FAST). Specifically, Dy3Si2C2 was selected as the representation of Re3Si2C2 since Dy is relatively chemical stable among the lanthanides, which is expected to minimize the formation the by-product oxide. The as-obtained joint show high strength, i.e. the joint fractured at the SiC matrix, but not the joint layer. This work implies the great potential of the family of ternary rare-earth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the interlayer for high-quality SiC joining. 2. Experimental The raw materials used to prepare the coating are 6H-SiC block (Zhejiang giant Rio Tinto seal Co., Ltd, Ningbo, China; size: φ20 × 20 mm), NaCl (Aladdim Industrial Co. Ltd, Shanghai, China; purity: 99.5%,) and Dy powders (Hunan Rare Earth Metal Materials 5458
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Fig. 3. (a)–(d) SEM images showing the joint layer of the sample joined at 1300 °C, 1400 °C, 1500 °C, and 1600 °C, respectively; (e) four-point bending strength of the SiC samples; (f) optical images of the 1600 °C samples after the four-point bending strength testing.
strength was tested using an Electric Universal Testing (AGS-X, 10N10KN, SHIMADZU, Japan) at room temperature. The Dy-Si-C phase diagram was conducted with the CALPHAD approach. The ab initio calculation indicated that the formation enthalpy for the Dy3Si2C2 phase was -61.77 kJ/mol-atom, which was used to determine the corresponding end-members. The 1 st and 2nd interaction parameters of the liquid phase were estimated to be −600 kJ/mol and −400 kJ/mol, respectively. With the thermodynamic description for the Dy-Si-C system, the phase diagrams and isothermal sections were carried out by using the Thermo-Calc software [19].
100 °C/min under the protection of Ar gas. The dwelling time is 10 min, and a uniaxial pressure of 50 MPa was set in dwelling stage. The morphology of the sample was investigated by a scanning electron microscope (FEI Quanta FEG 250) and transmission electron microscopy (TEM, Talos F200x, USA) equipped with an energy dispersive spectroscopy (EDS) system. The sample for TEM observation was prepared by a Focused Ion Beam (FIB, Auiga, Carl Zeiss AG). The phase compositions of the sample were analyzed by XRD (D8 Advance, Bruker AXS, Germany) using Cu Kα radiation. The joint samples were cut into to rectangular bars with the size of 3 × 4 × 40 mm and polished for four-point bending strength testing. Four-point bending 5459
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Fig. 4. (a) and (c) TEM image and corresponding EDS map showing the morphology and element distributions of the joint layer of 1500 °C sample; (b) highresolution transmission electron micrograph (HR-TEM) of the marked area in Fig. 4a. The electron beam is parallel to [10 1¯ 0] direction for the left side and parallel to [11 2¯ 0] direction for the right side, and Fast Fourier Transforms (FFTs) are given in the insets; (d) calculated phase diagrams of the Dy-Si-C system: isothermal section at 1400 °C; (e) isothermal section at 1500 °C；(f) schematic diagram showing the joining process.
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Fig. 5. Joining temperature and thickness of residual interlayer of silicon carbide joined with different interlayer materials [21].
3. Results and discussion
layer strength than that of the 1300 °C and 1400 °C samples. For the 1600 °C samples, all the samples for four-point bending test are fractured at the matrix (Fig. 3f). It indicates that the strength of the joint layer is higher than the SiC matrix, and a high-quality SiC joining was achieved.
3.1. Characterization of Dy3Si2C2 coating Fig. 2b is the TEM image showing the cross-section of the coating and the corresponding EDS map showing the element distribution (Fig. 2c). It can be seen that the Dy3Si2C2 coating with the thickness of ∼700 nm was uniformly coated on the surface of SiC. Note that a thin layer of Dy2O3 was located at the surface of Dy3Si2C2. The existence of Dy2O3 is reasonable since Dy could be oxidized easily with the presence of oxygen. The XRD patterns of the sample (Fig. 2a) confirmed that the coating is composed of the major phase Dy3Si2C2 (JCPDS card No.: 702795) and minor phase Dy2O3 (JCPDS card No.: 22-0612). The formation of Dy3Si2C2 coating is similar to the previous case of the formation of Ti3SiC2 and Ti2AlC coating on carbon and SiC [16,20]. Metal Dy powders first dissolved in the molten salts, and then diffused to the surface of SiC to the in-situ formed Dy3Si2C2 coating according to the following reaction:
3.3. Characterization of microstructure and phase evolution It is clear that a dramatic phase change of interlayer occurred between 1400 °C–1500 °C and resulted in the seamless joining. Therefore, the joint layer of the 1500 °C sample was investigated by TEM (Fig. 4a) to understand the joining mechanism. It can be seen that no Dy3Si2C2 retained in joining area, while some Dy2O3 was observed (Fig. 4a and c). The HR-TEM image confirmed that the two sides of SiC were directly bonded at the interface, without the presence of second phase (Fig. 4b). In order to understand the joining mechanism, we have further calculated the phase diagram of the Dy-Si-C system. Isothermal sections of the phase diagram at 1400 °C and 1500 °C are shown in Fig. 4d and e. The Dy3Si2C2 phase is stable at 1400 °C and there exists a two-phase region Dy3Si2C2 + SiC. However, when the temperature increased to 1500 °C, the Dy3Si2C2 phase is melted due to the ternary eutectic reaction at ∼1432 °C: L⇌ SiC + DySi + Dy3Si2C2. Apparently, for the joining process in the present work, there is no DySi phase because of the specific atomic molar ratio of Si/C. The phase diagram is in agreement with the experimental results. At 1300 °C and 1400 °C, the Dy3Si2C2 phase is stable and the SiC is joined by atom-level inter-diffusion at the interlayer with considerable interlayer retained in the final joined samples. In contrast, as shown in Fig. 4f, when the temperature increased to 1500 °C, a liquid phase is formed at the interface between SiC and Dy3Si2C2, and is continuously squeezed out under the pressure and consumed by the joining interlayer. At the final stage, part of Dy2O3 was brought out with the squeezing out of liquid phase, while not thoroughly. It should be pointed out that the high active liquid-solid interface also facilitates the atomic inter-diffusion, which promotes the direct interface bonding between the two sides of SiC. As a result, the high-quality SiC joint with a small amount of Dy2O3 at the joint layer was obtained. Notably, the joining mechanism in the present work can be concluded as an interlayer consuming process. Due to the squeezing out of liquid phase at the interlayer, mass transfer was largely accelerated and seamless joining was achieved in a short time at relatively low temperature. In contrast, the traditional joining mechanism is achieve by inter-diffusion, thus the interlayer can hardly be diminished although at higher joining temperature. We have concluded the thickness of residual interlayer of silicon carbide joined with different interlayer materials (Fig. 5). For most of the interlayer materials, e.g. Mo,
3Dy+2SiC→Dy3Si2C2
3.2. Characterization of the joined SiC couples and mechanical properties Fig. 3a–d shows the morphology of the joint layer of the samples joined at 1300 °C, 1400 °C, 1500 °C, and 1600 °C, respectively. All the samples were joined successfully. For the 1300 °C and 1400 °C samples, interlayer with the thickness of 3.5 μm and 3.0 μm were retained. In contrast, when the joining temperature increased to 1500 °C, the interlayer almost disappears and only several small particles (Dy2O3) retained. It indicates that the Dy3Si2C2 may have remarkable phase change that can promote the joining process. For the 1600 °C sample, the residual particles further decreased and seamless joining was achieved. The corresponding flexural-tensile strengths viafour-point bending test were shown in Fig. 3e. The strength of the SiC samples joined at 1300 °C, 1400 °C, 1500 °C and 1600 °C are 97.0 ± 21 MPa, 56.2 ± 16.3 MPa, 124.6 ± 17 MPa and 164.8 ± 23.1 MPa, respectively. The samples joined at 1300 °C and 1400 °C were directly fractured at the joint layer, indicating that the joint layer is relatively weak and is in agreement with the SEM observation. Note that the strengths of 1400 °C sample is low than that of 1300 °C sample, which may attribute to some incomplete phase change of the interlayer at around 1400 °C, deteriorating the strength (the phase change will be discussed later). Note that the 1500 °C sample also fractured at the joint layer while the cracks propagated to the SiC matrix, indicating a higher joint 5461
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Al-Ti, and Y2O3-Al2O3-SiO2, the residual thickness is considerably high. The seamless joining of SiC can be achieved through direct boning, whereas very high temperature (1900 °C) is required. In contrast, Dy3Si2C2 shows specific superiority in the residual interlayer thickness and joining temperature.
future nuclear systems, Scr. Mater. 143 (2018) 149–153. [4] W.B. Tian, H. Kita, H. Hyuga, N. Kondo, Joining of SiC by Al infiltrated TiC tape: effect of joining parameters on the microstructure and mechanical properties, J. Eur. Ceram. Soc. 32 (1) (2012) 149–156. [5] S. Grasso, P. Tatarko, S. Riozzo, H. Porwal, C.H. Hu, Y. Katoh, M. Salvo, M.J. Reece, M. Ferraris, Joining of β-SiC by spark plasma sintering, J. Eur. Ceram. Soc. 34 (2014) 1681–1686. [6] G. Liu, X. Zhang, J. Yang, G. Qiao, Recent advances in joining of SiC-based materials (monolithic SiC and SiCf/SiC composites): joining processes, joint strength, and interfacial behavior, J. Adv. Ceram. 8 (1) (2019) 19–38. [7] H. Yang, X. Zhou, W. Shi, J. Wang, P. Li, F. Chen, Q. Deng, J. Lee, Y.H. Han, F. Huang, L. He, S. Du, Q. Huang, Thickness-dependent phase evolution and bonding strength of SiC ceramics joints with active Ti interlayer, J. Eur. Ceram. Soc. 37 (4) (2017) 1233–1241. [8] B.V. Cockeram, Flexural strength and shear strength of silicon carbide to silicon carbide joints fabricated by a molybdenum diffusion bonding technique, J. Am. Ceram. Soc. 88 (7) (2005) 1892–1899. [9] Q.Y. Tong, L.F. Cheng, Liquid infiltration joining of 2D C/SiC composite, Sci Eng Compos Mater. 13 (2006) 31–36. [10] F. Valenza, S. Gambaro, M.L. Muolo, M. Salvo, V. Casalegno, Wetting of SiC by Al-Ti alloys and joining by in-situ formation of interfacial Ti3Si(Al)C2, J. Eur. Ceram. Soc. 38 (11) (2018) 3727–3734. [11] G.W. Liu, G.J. Qiao, H.J. Wang, J.F. Yang, T.J. Lu, Pressureless brazing of zirconia to stainless steel with Ag–Cu filler metal and TiH2 powder, J. Eur. Ceram. Soc. 28 (14) (2008) 2701–2708. [12] W. Tian, H. Kita, H. Hyuga, N. Kondo, T. Nagaoka, Reaction joining of SiC ceramics using TiB2-based composites, J. Eur. Ceram. Soc. 30 (15) (2010) 3203–3208. [13] M. Herrmann, W. Lippmann, A. Hurtado, High-temperature stability of laser-joined silicon carbide components, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 443 (1–3) (2013) 458–466. [14] F. Döhler, T. Zscheckel, S. Kasch, T. Schmidt, C. Rüssel, A glass in the CaO/MgO/ Al2O3/SiO2 System for the rapid laser sealing of alumina, Ceram. Int. 43 (5) (2017) 4302–4308. [15] X. Zhou, Y.H. Han, X. Shen, S. Du, J. Lee, Q. Huang, Fast joining SiC ceramics with Ti3SiC2 tape film by electric field-assisted sintering technology, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 466 (2015) 322–327. [16] M. Li, F. Chen, X. Si, J. Wang, S. Du, Q. Huang, Copper–SiC whiskers composites with interface optimized by Ti3SiC2, J. Mater. Sci. 53 (13) (2018) 9806–9815. [17] J. Shao, M. Li, K. Chang, Y. Huang, D. Ren, J. Wang, X. Zhou, L. He, F. Huang, S. Du, J. Sha, Z. Huang, Q. Huang, Fabrication and characterization of SPS sintered SiCbased ceramic from Y3Si2C2-coated SiC powders, J. Eur. Ceram. Soc. 38 (15) (2018) 4833–4841. [18] M.H. Gerdes, A.M. Witte, W. Jeitschko, A. Lang, B. Künnen, Magnetic and electrical properties of a new series of rare earth silicide carbides with the composition R3Si2C2 (R=Y, La-Nd, Gd-Tm), J. Solid State Chem. 138 (1998) 201–206. [19] B. Sundman, B. Jansson, J.O. Andersson, The Thermo-Calc databank system, Calphad. 9 (1985) 153–190. [20] M. Li, K. Wang, J. Wang, D. Long, Y. Liang, L. He, F. Huang, S. Du, Q. Huang, Preparation of TiC/Ti2AlC coating on carbon fiber and investigation of the oxidation resistance properties, J. Am. Ceram. Soc. 101 (11) (2018) 5269–5280. [21] M. Herrmann, W. Lippmann, A. Hurtado, Y2O3–Al2O3–SiO2-based glass-ceramic fillers for the laser-supported joining of SiC, J. Eur. Ceram. Soc. 43 (8) (2014) 1935–1948.
4. Conclusions In summary, rare-earth carbide Dy3Si2C2 coating was fabricated on the surface of SiC through a molten salt technique. Seamless joining of SiC ceramic was achieved at 1500 °C by using the Dy3Si2C2 coating as the joining interlayer. The joining mechanism can be described as a specific interlayer consuming process that includes the formation of liquid eutectic phase between Dy3Si2C2 and SiC, and the following squeezing out of the liquid phase. The as-obtained joint shows high strength, i.e. the strength of joining layer joined at 1600 °C is higher than that of the SiC matrix. This work implies the great potential of the family of ternary rare-earth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the interlayer for high-quality SiC joining at low temperatures. More importantly, by using the molten salt technique, thickness controllable coating can be easily fabricated on large-sized and complex-shaped SiC device, which may contribute to the high-quality SiC joining for practical applications, such as ceramic nuclear cladding tubes and heat sink part in semiconductor device. Disclosure statement No potential conflict of interest was reported by the authors. Acknowledgements This study was supported financially by the National Natural Science Foundation of China (grant NO. 21671195 and 91426304), and Key Technologies R&D Program (2017YFB0702401). References [1] L.L. Snead, T. Nozawa, Y. Katoh, T.S. Byun, S. Kondo, D.A. Petti, Handbook of SiC properties for fuel performance modeling, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 371 (1–3) (2007) 329–377. [2] R.G. Munro, Material properties of a sintered α-SiC, J. Phys. Chem. Ref. Data 26 (5) (1997) 1195–1203. [3] M. Li, X. Zhou, H. Yang, S. Du, Q. Huang, The critical issues of SiC materials for
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Contents lists available at ScienceDirect
Journal of the European Ceramic Society journal homepage: www.elsevier.com/locate/jeurceramsoc
Short communication
Seamless joining of silicon carbide ceramics through an sacrificial interlayer of Dy3Si2C2
T
⁎
Peng Wana,b,1, Mian Lib,1, Kai Xub, Haibo Wuc, Keke Changb, Xiaobing Zhoub, Xiangdong Dinga, , ⁎ Zhengren Huangb, Hongxiang Zonga, Qing Huangb, a
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xian, Shaanxi, 710049, China Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang, 315201, China c State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Joining Silicon carbide Ternary carbide Molten salt
A ternary carbide Dy3Si2C2 coating was fabricated on the surface of SiC through a molten salt technique. Using the Dy3Si2C2 coating as the joining interlayer, seamless joining of SiC ceramic was achieved at temperature as low as 1500 °C. Phase diagram calculation indicates that seamless joining was achieved by the formation of liquid phase at the interface between Dy3Si2C2 and SiC, which was squeezed out under pressure and continuously consumed by the joining interlayer. This work implies the great potential of the family of ternary rareearth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the sacrificial interlayer for high-quality SiC joining.
1. Introduction Silicon carbide (SiC) has the properties of low density, high strength, good high temperature stability, good corrosion resistance, and low neutron-induced activation, [1–3], which makes it a promising candidate for aerospace structural material, electronics device, and nuclear structural material. The strong Si-C covalent bond endows SiC high hardness, intrinsic brittleness and low self-diffusivity coefficient, which makes it difficult to be formed and manufactured in near netshape. Therefore, joining is considered to be an effective way to obtain large-sized and complex-shaped SiC components [4]. In the last decades, direct bonding and indirect bonding method have been developed for SiC joining. Direct bonding is achieved by inter-diffusion between SiC couples, which requires high joining temperature (∼1900 °C) and high pressure [5]. Indirect joining is achieved by adding a joining interlayer between SiC couples that can promote atom diffusion and decrease the joining temperature. Therefore, choosing suitable interlayer materials is critically important for highquality SiC joining [6]. So far, variety of interlayer materials have been explored for SiC joining, such as full metallic interlayer (Ti, Mo, Ni, AlTi, and Ag-Cu [7–11]), metal-ceramic hybrid interlayer (Al-TiC, Ti-B4CSi, and Ti-BN-Al [4,12]), glass-ceramic interlayer (Y2O3-Al2O3-SiO2, CaO-MgO-Al2O3-SiO2 [13,14]), and MAX phase interlayer (Ti3SiC2
[15]). Most of these interlayers retained in the final SiC joint, which is harmful to the stability of SiC joint when exposed in extreme environments, e.g. high temperature, severe oxidation/corrosion and irradiation environment. Moreover, the thermal mismatch between SiC and interlayer results in residual stress, which decreases the stability of the joint. Therefore, in the last years, researchers show great interests in exploring suitable joining strategy to achieve seamless SiC joining. In our previous work, we have developed a molten salts technique that can fabricate metal carbides (e.g. Ti3SiC2 and Y3Si2C2) coating on SiC fibers and SiC powders [16,17]. By using Y3Si2C2 coated SiC powders as the starting materials, fully dense SiC ceramic was obtained through spark plasma sintering (SPS) at 1700 °C [17]. The densification of SiC ceramic was promoted by the formation of eutectic phase between Y3Si2C2 and SiC, which can accelerate the atom diffusion and grain growth. Notably, the as-formed liquid phase was extruded during the sintering process, thus the as-obtained SiC ceramics contains no residual Y3Si2C2 but a little by-product Y2O3. Note that Y3Si2C2 have a family of ternary rare-earth carbides with similar structure, i.e. Re3Si2C2 (Re = Y, La-Nd) [18]. The family of Re3Si2C2 are expected to have similar properties with Y3Si2C2, which may be used to promote the sintering and seamless joining of SiC. In the present work, a Dy3Si2C2 coating was fabricated on the surface of SiC through the molten salt technique. By using the Dy3Si2C2 coating as the joining interlayer,
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Corresponding authors. E-mail addresses: [email protected] (X. Ding), [email protected] (Q. Huang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jeurceramsoc.2019.09.002 Received 31 July 2019; Received in revised form 30 August 2019; Accepted 1 September 2019 Available online 03 September 2019 0955-2219/ © 2019 Elsevier Ltd. All rights reserved.
Journal of the European Ceramic Society 39 (2019) 5457–5462
P. Wan, et al.
Fig. 1. Schematic diagram showing the Dy3Si2C2 coating fabricating process.
Fig. 2. Characterization of the Dy3Si2C2 coating: (a) XRD patterns of coating and substrate; (b), (c) TEM image showing the cross-section of the coating and corresponding EDS map showing the element distribution.
Research Institute, Hunan, China; purity: 99.5%, mean particle size: 75 μm). The schematic diagram of the fabricating process was shown in Fig. 1. First, the SiC block was placed in an alumina crucible. After that, Dy powder and NaCl salt with the mass ratio of 1:10 was mixed thoroughly using a mortar under the protection of nitrogen in a glovebox. Then the NaCl/Dy mixture was placed into alumina crucible and covered the SiC block. The alumina crucible was loaded into a tube furnace and heat treated at 900 °C for 60 min under the protection of Ar gas. Then the tube furnace was naturally cooled to the room temperature. After that, the product was washed by deionized water for five times to remove the residual NaCl and Dy. Finally, the SiC block with Dy3Si2C2 coating was obtained. Two as-obtained Dy3Si2C2 coated SiC blocks were put into a graphite die to perform the joining. The graphite die was then loaded into a SPS furnace (HP D25/1, FCT Systeme GmbH, Rauenstein, Germany) and heated to target temperature (1300 °C–1600 °C) with a rate of
seamless joining of SiC ceramic was achieved at the temperature as low as 1500 °C through an electric current field-assisted sintering technology (FAST). Specifically, Dy3Si2C2 was selected as the representation of Re3Si2C2 since Dy is relatively chemical stable among the lanthanides, which is expected to minimize the formation the by-product oxide. The as-obtained joint show high strength, i.e. the joint fractured at the SiC matrix, but not the joint layer. This work implies the great potential of the family of ternary rare-earth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the interlayer for high-quality SiC joining. 2. Experimental The raw materials used to prepare the coating are 6H-SiC block (Zhejiang giant Rio Tinto seal Co., Ltd, Ningbo, China; size: φ20 × 20 mm), NaCl (Aladdim Industrial Co. Ltd, Shanghai, China; purity: 99.5%,) and Dy powders (Hunan Rare Earth Metal Materials 5458
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Fig. 3. (a)–(d) SEM images showing the joint layer of the sample joined at 1300 °C, 1400 °C, 1500 °C, and 1600 °C, respectively; (e) four-point bending strength of the SiC samples; (f) optical images of the 1600 °C samples after the four-point bending strength testing.
strength was tested using an Electric Universal Testing (AGS-X, 10N10KN, SHIMADZU, Japan) at room temperature. The Dy-Si-C phase diagram was conducted with the CALPHAD approach. The ab initio calculation indicated that the formation enthalpy for the Dy3Si2C2 phase was -61.77 kJ/mol-atom, which was used to determine the corresponding end-members. The 1 st and 2nd interaction parameters of the liquid phase were estimated to be −600 kJ/mol and −400 kJ/mol, respectively. With the thermodynamic description for the Dy-Si-C system, the phase diagrams and isothermal sections were carried out by using the Thermo-Calc software [19].
100 °C/min under the protection of Ar gas. The dwelling time is 10 min, and a uniaxial pressure of 50 MPa was set in dwelling stage. The morphology of the sample was investigated by a scanning electron microscope (FEI Quanta FEG 250) and transmission electron microscopy (TEM, Talos F200x, USA) equipped with an energy dispersive spectroscopy (EDS) system. The sample for TEM observation was prepared by a Focused Ion Beam (FIB, Auiga, Carl Zeiss AG). The phase compositions of the sample were analyzed by XRD (D8 Advance, Bruker AXS, Germany) using Cu Kα radiation. The joint samples were cut into to rectangular bars with the size of 3 × 4 × 40 mm and polished for four-point bending strength testing. Four-point bending 5459
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Fig. 4. (a) and (c) TEM image and corresponding EDS map showing the morphology and element distributions of the joint layer of 1500 °C sample; (b) highresolution transmission electron micrograph (HR-TEM) of the marked area in Fig. 4a. The electron beam is parallel to [10 1¯ 0] direction for the left side and parallel to [11 2¯ 0] direction for the right side, and Fast Fourier Transforms (FFTs) are given in the insets; (d) calculated phase diagrams of the Dy-Si-C system: isothermal section at 1400 °C; (e) isothermal section at 1500 °C；(f) schematic diagram showing the joining process.
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Fig. 5. Joining temperature and thickness of residual interlayer of silicon carbide joined with different interlayer materials [21].
3. Results and discussion
layer strength than that of the 1300 °C and 1400 °C samples. For the 1600 °C samples, all the samples for four-point bending test are fractured at the matrix (Fig. 3f). It indicates that the strength of the joint layer is higher than the SiC matrix, and a high-quality SiC joining was achieved.
3.1. Characterization of Dy3Si2C2 coating Fig. 2b is the TEM image showing the cross-section of the coating and the corresponding EDS map showing the element distribution (Fig. 2c). It can be seen that the Dy3Si2C2 coating with the thickness of ∼700 nm was uniformly coated on the surface of SiC. Note that a thin layer of Dy2O3 was located at the surface of Dy3Si2C2. The existence of Dy2O3 is reasonable since Dy could be oxidized easily with the presence of oxygen. The XRD patterns of the sample (Fig. 2a) confirmed that the coating is composed of the major phase Dy3Si2C2 (JCPDS card No.: 702795) and minor phase Dy2O3 (JCPDS card No.: 22-0612). The formation of Dy3Si2C2 coating is similar to the previous case of the formation of Ti3SiC2 and Ti2AlC coating on carbon and SiC [16,20]. Metal Dy powders first dissolved in the molten salts, and then diffused to the surface of SiC to the in-situ formed Dy3Si2C2 coating according to the following reaction:
3.3. Characterization of microstructure and phase evolution It is clear that a dramatic phase change of interlayer occurred between 1400 °C–1500 °C and resulted in the seamless joining. Therefore, the joint layer of the 1500 °C sample was investigated by TEM (Fig. 4a) to understand the joining mechanism. It can be seen that no Dy3Si2C2 retained in joining area, while some Dy2O3 was observed (Fig. 4a and c). The HR-TEM image confirmed that the two sides of SiC were directly bonded at the interface, without the presence of second phase (Fig. 4b). In order to understand the joining mechanism, we have further calculated the phase diagram of the Dy-Si-C system. Isothermal sections of the phase diagram at 1400 °C and 1500 °C are shown in Fig. 4d and e. The Dy3Si2C2 phase is stable at 1400 °C and there exists a two-phase region Dy3Si2C2 + SiC. However, when the temperature increased to 1500 °C, the Dy3Si2C2 phase is melted due to the ternary eutectic reaction at ∼1432 °C: L⇌ SiC + DySi + Dy3Si2C2. Apparently, for the joining process in the present work, there is no DySi phase because of the specific atomic molar ratio of Si/C. The phase diagram is in agreement with the experimental results. At 1300 °C and 1400 °C, the Dy3Si2C2 phase is stable and the SiC is joined by atom-level inter-diffusion at the interlayer with considerable interlayer retained in the final joined samples. In contrast, as shown in Fig. 4f, when the temperature increased to 1500 °C, a liquid phase is formed at the interface between SiC and Dy3Si2C2, and is continuously squeezed out under the pressure and consumed by the joining interlayer. At the final stage, part of Dy2O3 was brought out with the squeezing out of liquid phase, while not thoroughly. It should be pointed out that the high active liquid-solid interface also facilitates the atomic inter-diffusion, which promotes the direct interface bonding between the two sides of SiC. As a result, the high-quality SiC joint with a small amount of Dy2O3 at the joint layer was obtained. Notably, the joining mechanism in the present work can be concluded as an interlayer consuming process. Due to the squeezing out of liquid phase at the interlayer, mass transfer was largely accelerated and seamless joining was achieved in a short time at relatively low temperature. In contrast, the traditional joining mechanism is achieve by inter-diffusion, thus the interlayer can hardly be diminished although at higher joining temperature. We have concluded the thickness of residual interlayer of silicon carbide joined with different interlayer materials (Fig. 5). For most of the interlayer materials, e.g. Mo,
3Dy+2SiC→Dy3Si2C2
3.2. Characterization of the joined SiC couples and mechanical properties Fig. 3a–d shows the morphology of the joint layer of the samples joined at 1300 °C, 1400 °C, 1500 °C, and 1600 °C, respectively. All the samples were joined successfully. For the 1300 °C and 1400 °C samples, interlayer with the thickness of 3.5 μm and 3.0 μm were retained. In contrast, when the joining temperature increased to 1500 °C, the interlayer almost disappears and only several small particles (Dy2O3) retained. It indicates that the Dy3Si2C2 may have remarkable phase change that can promote the joining process. For the 1600 °C sample, the residual particles further decreased and seamless joining was achieved. The corresponding flexural-tensile strengths viafour-point bending test were shown in Fig. 3e. The strength of the SiC samples joined at 1300 °C, 1400 °C, 1500 °C and 1600 °C are 97.0 ± 21 MPa, 56.2 ± 16.3 MPa, 124.6 ± 17 MPa and 164.8 ± 23.1 MPa, respectively. The samples joined at 1300 °C and 1400 °C were directly fractured at the joint layer, indicating that the joint layer is relatively weak and is in agreement with the SEM observation. Note that the strengths of 1400 °C sample is low than that of 1300 °C sample, which may attribute to some incomplete phase change of the interlayer at around 1400 °C, deteriorating the strength (the phase change will be discussed later). Note that the 1500 °C sample also fractured at the joint layer while the cracks propagated to the SiC matrix, indicating a higher joint 5461
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Al-Ti, and Y2O3-Al2O3-SiO2, the residual thickness is considerably high. The seamless joining of SiC can be achieved through direct boning, whereas very high temperature (1900 °C) is required. In contrast, Dy3Si2C2 shows specific superiority in the residual interlayer thickness and joining temperature.
future nuclear systems, Scr. Mater. 143 (2018) 149–153. [4] W.B. Tian, H. Kita, H. Hyuga, N. Kondo, Joining of SiC by Al infiltrated TiC tape: effect of joining parameters on the microstructure and mechanical properties, J. Eur. Ceram. Soc. 32 (1) (2012) 149–156. [5] S. Grasso, P. Tatarko, S. Riozzo, H. Porwal, C.H. Hu, Y. Katoh, M. Salvo, M.J. Reece, M. Ferraris, Joining of β-SiC by spark plasma sintering, J. Eur. Ceram. Soc. 34 (2014) 1681–1686. [6] G. Liu, X. Zhang, J. Yang, G. Qiao, Recent advances in joining of SiC-based materials (monolithic SiC and SiCf/SiC composites): joining processes, joint strength, and interfacial behavior, J. Adv. Ceram. 8 (1) (2019) 19–38. [7] H. Yang, X. Zhou, W. Shi, J. Wang, P. Li, F. Chen, Q. Deng, J. Lee, Y.H. Han, F. Huang, L. He, S. Du, Q. Huang, Thickness-dependent phase evolution and bonding strength of SiC ceramics joints with active Ti interlayer, J. Eur. Ceram. Soc. 37 (4) (2017) 1233–1241. [8] B.V. Cockeram, Flexural strength and shear strength of silicon carbide to silicon carbide joints fabricated by a molybdenum diffusion bonding technique, J. Am. Ceram. Soc. 88 (7) (2005) 1892–1899. [9] Q.Y. Tong, L.F. Cheng, Liquid infiltration joining of 2D C/SiC composite, Sci Eng Compos Mater. 13 (2006) 31–36. [10] F. Valenza, S. Gambaro, M.L. Muolo, M. Salvo, V. Casalegno, Wetting of SiC by Al-Ti alloys and joining by in-situ formation of interfacial Ti3Si(Al)C2, J. Eur. Ceram. Soc. 38 (11) (2018) 3727–3734. [11] G.W. Liu, G.J. Qiao, H.J. Wang, J.F. Yang, T.J. Lu, Pressureless brazing of zirconia to stainless steel with Ag–Cu filler metal and TiH2 powder, J. Eur. Ceram. Soc. 28 (14) (2008) 2701–2708. [12] W. Tian, H. Kita, H. Hyuga, N. Kondo, T. Nagaoka, Reaction joining of SiC ceramics using TiB2-based composites, J. Eur. Ceram. Soc. 30 (15) (2010) 3203–3208. [13] M. Herrmann, W. Lippmann, A. Hurtado, High-temperature stability of laser-joined silicon carbide components, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 443 (1–3) (2013) 458–466. [14] F. Döhler, T. Zscheckel, S. Kasch, T. Schmidt, C. Rüssel, A glass in the CaO/MgO/ Al2O3/SiO2 System for the rapid laser sealing of alumina, Ceram. Int. 43 (5) (2017) 4302–4308. [15] X. Zhou, Y.H. Han, X. Shen, S. Du, J. Lee, Q. Huang, Fast joining SiC ceramics with Ti3SiC2 tape film by electric field-assisted sintering technology, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 466 (2015) 322–327. [16] M. Li, F. Chen, X. Si, J. Wang, S. Du, Q. Huang, Copper–SiC whiskers composites with interface optimized by Ti3SiC2, J. Mater. Sci. 53 (13) (2018) 9806–9815. [17] J. Shao, M. Li, K. Chang, Y. Huang, D. Ren, J. Wang, X. Zhou, L. He, F. Huang, S. Du, J. Sha, Z. Huang, Q. Huang, Fabrication and characterization of SPS sintered SiCbased ceramic from Y3Si2C2-coated SiC powders, J. Eur. Ceram. Soc. 38 (15) (2018) 4833–4841. [18] M.H. Gerdes, A.M. Witte, W. Jeitschko, A. Lang, B. Künnen, Magnetic and electrical properties of a new series of rare earth silicide carbides with the composition R3Si2C2 (R=Y, La-Nd, Gd-Tm), J. Solid State Chem. 138 (1998) 201–206. [19] B. Sundman, B. Jansson, J.O. Andersson, The Thermo-Calc databank system, Calphad. 9 (1985) 153–190. [20] M. Li, K. Wang, J. Wang, D. Long, Y. Liang, L. He, F. Huang, S. Du, Q. Huang, Preparation of TiC/Ti2AlC coating on carbon fiber and investigation of the oxidation resistance properties, J. Am. Ceram. Soc. 101 (11) (2018) 5269–5280. [21] M. Herrmann, W. Lippmann, A. Hurtado, Y2O3–Al2O3–SiO2-based glass-ceramic fillers for the laser-supported joining of SiC, J. Eur. Ceram. Soc. 43 (8) (2014) 1935–1948.
4. Conclusions In summary, rare-earth carbide Dy3Si2C2 coating was fabricated on the surface of SiC through a molten salt technique. Seamless joining of SiC ceramic was achieved at 1500 °C by using the Dy3Si2C2 coating as the joining interlayer. The joining mechanism can be described as a specific interlayer consuming process that includes the formation of liquid eutectic phase between Dy3Si2C2 and SiC, and the following squeezing out of the liquid phase. The as-obtained joint shows high strength, i.e. the strength of joining layer joined at 1600 °C is higher than that of the SiC matrix. This work implies the great potential of the family of ternary rare-earth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the interlayer for high-quality SiC joining at low temperatures. More importantly, by using the molten salt technique, thickness controllable coating can be easily fabricated on large-sized and complex-shaped SiC device, which may contribute to the high-quality SiC joining for practical applications, such as ceramic nuclear cladding tubes and heat sink part in semiconductor device. Disclosure statement No potential conflict of interest was reported by the authors. Acknowledgements This study was supported financially by the National Natural Science Foundation of China (grant NO. 21671195 and 91426304), and Key Technologies R&D Program (2017YFB0702401). References [1] L.L. Snead, T. Nozawa, Y. Katoh, T.S. Byun, S. Kondo, D.A. Petti, Handbook of SiC properties for fuel performance modeling, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 371 (1–3) (2007) 329–377. [2] R.G. Munro, Material properties of a sintered α-SiC, J. Phys. Chem. Ref. Data 26 (5) (1997) 1195–1203. [3] M. Li, X. Zhou, H. Yang, S. Du, Q. Huang, The critical issues of SiC materials for
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