Wetting and brazing of Cf/C composites with Si–Zr eutectic alloys: The formation of nano- and coarse-SiC reaction layers

Abstract

The wetting and brazing of Cf/C composites with a Si–10Zr eutectic alloy was investigated for the first time. Wetting of the Si–Zr alloy on the Cf/C substrate was studied by applying in-situ variations in contact angle of the droplet placed on the Cf/C substrate with temperature and time. The microstructure and the interfacial structure between the filler and the substrate, and the mechanical properties of the joints were determined using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The Si–Zr alloy has an equilibrium contact angle of approximately 22° on the Cf/C substrate at 1460 °C, indicating excellent wettability. The liquid Si–Zr alloy can react with the Cf/C substrate by forming nano-SiC and coarse-SiC layers, and promote the wetting behaviour and bonding performance. In addition, the liquid Si–Zr alloy can also infiltrate into the Cf/C substrate along the carbon fibres, causing localised siliconisation and strengthening of the joint. An optimal shear strength of 32 MPa was achieved for the joint at a brazing temperature of 1460 °C for 10 min.