Microstructure evolution and shear strength of vacuum brazed joint for super-Ni/NiCr laminated composite with Ni–Cr–Si–B amorphous interlayer

Vacuum brazing of super-Ni/NiCr laminated composite and Cr18–Ni8 steel was carried out with Ni–Cr–Si–B amorphous interlayer at different temperatures (1060–1150 °C). The effects of brazing temperature on the microstructure evolution and shear strength of the joints were investigated. Microstructure, chemical composition and microhardness of the joints were studied using field emission scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction and microsclerometer. Shear strength of the joints were measured by the electromechanical universal testing machine. Diffusion of B was the controlling factor for microstructure evolution. The detailed isothermal solidification mechanism was proposed in this study. The fracture morphology of the joint made at 1100 °C exhibited plastic feature and the shear strength reached 191 MPa. Bulky Ni3B formed in super-Ni cover layer near the brazed region when performed at 1060–1100 °C while Ni–B eutectic formed instead at 1150 °C.