Joining of C f /SiBCN Composite with a Ni-Cr-Pd(Si,B) Filler Alloy
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Joining of Cf/SiBCN Composite with a Ni-Cr-Pd(Si,B) Filler Alloy Wen-Wen Li, Bo Chen, Hua-Ping Xiong, Yao-Yong Cheng, and Wen-Jiang Zou1 (Submitted December 20, 2018; in revised form September 18, 2019) Joining of Cf/SiBCN composite was conducted by a newly designed Ni-Cr-Pd(Si,B) system filler alloy. The dynamic wettability on the Cf/SiBCN composite was measured by the sessile drop method. The joint microstructure and the fracture surface were analyzed by scanning electron microscope and x-ray diffraction spectrometer. The results showed that the Ni-Cr-Pd(Si,B) filler alloy exhibited a low contact angle of 11.6° on the composite after holding at 1170 °C for 30 min. Element Cr played an active role in the interfacial reaction, and a Cr7C3 reaction layer with a thickness of 8 µm was formed at the surface of the Cf/ SiBCN composite. Under the brazing condition of 1170 °C for 10 min, the joint strength at the room temperature reached 66.8 MPa. When the test temperature increased to 600 and 800 °C, the joint strength was even elevated to 90.3 and 81.2 MPa, respectively. The joint strength at high temperature was higher than that at room temperature, and this should be attributed to the improvement of the joint plasticity and the release of the residual thermal stresses within the brazed joint.
Keywords
Cf/SiBCN composite, joining, joint strength, microstructure, wettability
1. Introduction Amorphous silicon boron carbonitride (SiBCN) material has attracted growing attention over the past 20 years owing to its outstanding high-temperature properties (Ref 1, 2). The thermal stability of the SiBCN material in inert gases can be up to 2000 °C, and the oxidation resistance in air can be up to 1500 ° C (Ref 3-5). As a result, the SiBCN ceramics are considered to be utilized in aerospace and anti-ablation structures (nose caps, satellite nozzles, rocket engines, etc.) in future (Ref 6). Because continuous carbon fibers were embedded in the SiBCN matrix, the toughness and the thermal shock resistance of the Cf/SiBCN composite were improved remarkably (Ref 6, 7). As a result, the Cf/SiBCN composite has been a promising material for high-temperature structural components. The practical use of the composite requires development of appropriate joining techniques. In many cases, the joining of the composite to itself or to metals is also needed, and the joints must retain good high-temperature property. Nevertheless, the research on the Si-B-C-N ceramic itself has just started over the last two decades, and the understanding on its joining characteristic is rather lacking. Sun et al. (Ref 8) fabricated a functional gradient SiBCN-Nb composite by hot pressing, which can be used to the joining of dissimilar materials. The direct active brazing, due to its simplicity, lower cost investment and potential as a mass production process, can be considered as a proper joining technology for the SiBCN matrix Wen-Wen Li, Bo Chen, Hua-Ping Xiong, Yao-Yong Cheng, and Wen-Jiang Zou, Welding and Plastic Formin
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