Elsevier

Materials Characterization

Volume 155, September 2019, 109799
Materials Characterization

Joining of the Cf/SiC composites by a one-step Si infiltration reaction bonding

https://doi.org/10.1016/j.matchar.2019.109799Get rights and content

Highlights

  • The joining of the reaction-sintered Cf/SiC composite by a one-step Si infiltration process

  • The final densification and joining of the Cf/SiC were completed in the reaction bonding process.

  • The joints with high flexural strength was achieved (203 MPa), which is comparable to the Cf/SiC substrate (210 MPa).

  • The formation of the transition layer are dominant strengthening mechanisms

Abstract

An improved joining technique by reaction bonded technology was studied. The final densification and joining of the reaction-sintered composites were simultaneously completed in the reaction bonding process by one-step Si infiltration process. This method achieves joints with strong interfacial bonding and high flexural strength. The joint obtained by the one-step silicon infiltration reaction has a more uniform microstructure, the joint flexural strength is increased to 203 MPa, and retention rate of the flexural strength is 96%, which is comparable to the flexural strength of the Cf/SiC substrate. The microstructure and interfacial evolution mechanism of the interlayer were discussed. The results show that a transition layer of 2–3 μm transition layer formed between the interlayer and the Cf/SiC substrate, which is composed of SiC crystal grains of about 0.5–1 μm. The formation of the transition layer is due to the carbon concentration difference at the interface between interlayer and substrate, resulting in the diffusion of carbon during the Sisingle bondC reaction.

Introduction

Carbon fiber reinforced silicon carbide matrix composites (Cf/SiC) have received considerable attention for their excellent high-temperature performances, excellent corrosion resistance, high specific rigidity, high thermal conductivity and exhibits low density [1,2]. Thus, Cf/SiC composites are possible materials in many areas, such as high-temperature structural components, aerospace, national defense, energy, and so on [3,4].

However, it is almost impossible to fabricate Cf/SiC composites components by forging, extruding or other plastic forming processes due to its extreme hardness and brittle nature. The rapid development of aerospace, national defense, energy, and other fields has put forward urgent requirements for Cf/SiC components with the complex shape or large size. Therefore, the most popular approach for fabricating Cf/SiC components is to join small or simple composites pieces together to form the desired structures. At present, a wide range of technologies has been developed for joining Cf/SiC composites, such as metallic braze-based joining [5,6], MAX phase joining [7,8], glass-ceramic bonding [9], diffusion [10], polymer-derived SiC joining [11] and Sisingle bondC reaction joining [[12], [13], [14], [15], [16], [17]].

The method of Sisingle bondC reaction joining is to apply the reaction-sintered silicon carbide ceramic process to the joining of silicon carbide ceramic and its composite material. Compared with other joining methods, the method of reaction joining has the advantages of high joint strength, good matching of the interlayer and the substrate, high application temperature and controllable structure of the interlayer [12]. In previous work [[12], [13], [14]], a variety of SiC ceramics and ceramic matrix composites were joined using this method, and the mechanical properties of the joints were evaluated. M Singh [15] studied the effect of the base material and joining process parameters on the high-temperature mechanical properties of the joint formed by the Sisingle bondC reaction bonding. By measuring the electrical properties of the joint interface, Li, S.B [16] found no abrupt change in electrical resistivity around the joint area, which indicates that there is no steep gradient in the microstructure and properties of the Sisingle bondC reaction joint interface. Luo, Z.H [17] used SiC/C tapes with different composition and thickness to join a pressureless sintered silicon carbide ceramic by Sisingle bondC reaction bonding and obtained a sample having high bending strength by controlling the composition and thickness of the interlayer. However, the machining of the SiC ceramics and ceramic matrix composites before joining is quite difficult, and the process of silicon infiltration is repeated.

Besshi, T [18] found that the joining of green bodies before sintering is useful in obtaining complexly shaped Al2O3 ceramic parts and effective for reducing manufacturing costs. In this paper, an improved joining technique by reaction bonded technology was studied. The Cf/C preform was joined before the silicon infiltration process, and the joining process was applied at the stage of the siliconization. The final densification and joining of the reaction-sintered composites were simultaneously completed in the reaction bonding process. The most important advantage of this technology is that the joining of the reaction-sintered composite by a one-step Si infiltration process, avoiding the repeated silicon infiltration process. The microstructure and mechanical properties of the joint were studied. The interfacial evolution mechanism of the joint area was also discussed.

Section snippets

Experimental procedures

The materials used for joining in this paper include Cf/SiC composites and Cf/C perform, all of which are prepared in our laboratory. The microstructure of the Cf/C preform is shown in Fig. 1. The density and the 3-point flexural strength of the Cf/SiC composites and Cf/C preform in this study are 2.77 ± 0.03 g/cm3, 210 ± 22 MPa, and 0.94 g/cm3, 95 ± 10 MPa, respectively.

The precursor slurry, containing organic resin, solvent, dispersant, catalyst, and SiC powder, was used for joining. The

Microstructure of the joints

Fig. 3 presents the cross-section microstructure of the RB-OS joint and RB-TS joint. Microstructural studies and phase analysis reveal that both of the joints are well-bonded without cracks and voids, and the interlayer is basically ‘fully dense’. This one-step silicon infiltration reaction bonding method achieves an effective joining of the Cf/SiC composite. The interlayer thicknesses of the RB-OS (Fig. 3b) and RB-TS (Fig. 3a) joints are approximately 55 μm and 12 μm, respectively. The detail

Conclusions

It has been demonstrated that the one-step silicon infiltration reaction bonding can achieve a joint with strong interfacial bonding and high flexural strength. A transition layer of 2–3 μm transition layer formed between the interlayer and the Cf/SiC substrate, which is composed of SiC crystal grains of about 0.5–1 μm. The flexural strength of RB-OS joints reached 203 ± 24 MPa, which is comparable to the flexural strength of the Cf/SiC substrate. The more homogenous microstructure of

Acknowledgments

This work was supported by Natural Science Foundation of Shanghai (No. 16ZR1440900).

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