Microstructure of Ni–NiCr laminated composite and Cr18–Ni8 steel joint by vacuum brazing

Abstract

Vacuum brazing of Ni–NiCr laminated composite to Cr18–Ni8 steel was carried out using Ni–Cr–Si–B amorphous foil. Microstructure characteristic of the brazed joints was investigated by scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), field-emission scanning electron microscope (FE-SEM) and microsclerometer. Ni–Cr–Si–B amorphous foil exhibited good wettability on Ni–NiCr laminated composite. The brazed region consisted of γ-Ni solid solution and Ni–B eutectic. An excellent bonding with shear of 170 MPa was obtained. An interface of Ni3B precipitated in Ni cover layer near the brazed region. Microhardness of the interface was 500 HV. There was an interface consisting of fine boride granules in Cr18–Ni8 steel close to the brazed region and microhardness of the interface was 250 HV. Bonding behavior of the brazed joint was described according to the microstructure characteristic.