Investigations of the effect of Si addition on graphite elimination and the oxidation behavior of SiC joint using Inconel 625 powder filler

• Published in: Journal of the European Ceramic Society Vol. 42; no. 4; pp. 1258 - 1271
• Main Authors: Shi, Haojiang, Peng, Huabei, Yan, Jiazhen, Zhang, Ran, Li, Ning, Wen, Yuhua, Bai, Dong, Liu, Zihao, Chai, Yidi, Zhang, Ruiqian, Li, Ming, Chen, Kangwei, Luo, Mingliang, Sun, Qi, Li, Rui, Dong, Xin
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2022
• Subjects: Brazing; Graphite; Interface; Mechanical property; Oxidation; Brazing; Oxidation; Mechanical property; Interface; Graphite
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2021.11.055

•A method of avoiding graphite formation in SiC joint brazed by Inconel 625 is proposed in this paper. A graphite-free brazed seam is obtained when 23.1 wt% pure Si powder is blended with Inconel 625 powder.•The experimental results confirm the thermodynamic calculation results that Si content is highly associated with the liquid alloy's chemical potential. Once Si content reaches a critical value, the reactions between the liquid and SiC stops.•The oxidation performance at 800 °C in air of the SiC joint with graphite and the graphite-free SiC joint are compared in this paper. It shows that the brazed seam with graphite is seriously damaged due to the voloxidation of graphite, and the joint's shear strength decreases rapidly, while the graphite-free brazed seam maintains intact and the joint's shear strength decreases slightly. Graphite, whose presence is harmful to the mechanical property, is one of the main reaction products between Ni-based alloy and SiC. This paper reports a method of eliminating graphite based on thermodynamic calculations. Different amounts of Si powders are added into the Inconel 625 powder filler to adjust the interfacial reactions during the brazing process. When the Si content in the liquid reaches the theoretically calculated value, the reactions between the Inconel 625 filler and SiC substrate are suppressed, and no graphite forms on the interface. The graphite-free SiC joints show good oxidation resistance. The joint's strength maintains at 25.7 MPa while that with graphite drastically drops to 5.5 MPa after 185 h oxidation in air. The reaction products and oxidation process of the SiC joints are also carefully analyzed in this paper.