Induction brazing of cermets to steel

Abstract

The paper considers the induction brazing of TiC based cermets with Ni-Mo and Fe-Ni binder phase and Cr3C2 based cermets with Ni binder to structural and stainless steels under vacuum and air conditions. Commercially available traditional filler metals and experimental amorphous filler foils were tested. Possibility of mechanical metallizing of cermet surfaces with rotating Ti brushes prior to the brazing process was studied. Increase in the surface roughness after mechanical metallizing and non-uniform distribution of Ti on the treated surfaces were observed. Positive influence of electrochemically deposited Ag and Ni coatings on the shear strength of joints was found when optimal filler metals were used. Maximum shear strength up to 200-250 MPa was achieved with Ti- and Ni-based amorphous filler foils. Brazing in air by optimal fluxes and Ag- and Cu-based conventional brazing fillers can be used for brazing of cermets. Shear strength up to 150-190 MPa was achieved. The shear strength of vacuum brazed joints increases with the increase of the metal binder content in the cermet. Diffusion of the filler metal to base metal and to joint interface was studied by EPMA and SEM. It was found that cermets are successfully brazed with amorphous filler metals and the strength of the joints was not affected by the rapid heating during the induction process and relatively low vacuum.