Microstructure and fracture characteristics in vacuum brazed joint of super-Ni/NiCr laminated composite

摘要

The objective of this study is to investigate the brazeability of a new laminated composite with Ni-Cr-P filler metal in vacuum. Microstructure, microhardness and shear strength of the brazed joint were investigated by means of scanning electron microscopy, energy-dispersive spectroscopy, microsclerometer and electromechanical universal testing machine. Excellent joint of super-Ni/NiCr laminated composite to Cr18-Ni8 steel was obtained at 1040℃ for 20 min through vacuum brazing with Ni-Cr-P filler metal. Ni_2Cr particles precipitated in NiCr base layer under the influence of thermal cycle. The brazed region consisted of γ-Ni(Cr) solid solution and eutectic of γ-Ni(P) and Ni_3P. Microhardness of the eutectic was as high as 630 HV. Shear strength of the brazed joint was 137 MPa and the joint fractured in the eutectic. Steps and cracks formed in the fracture surface under the shear force.