Induction brazing of cermets to steel and eddy current testing of joint quality

The principal aim of the study was to demonstrate the feasibility of induction brazing of TiC-based cermets with Fe- and Ni-alloy binders under ambient atmosphere. A secondary aim was to investigate the possibility of using an innovative rapid non-destructive contactless testing method based on eddy current measurement for the evaluation of joint quality. Ag- and Cu-based filler metals and suitable fluxes developed for brazing of cemented carbides (WC-Co) to steels were employed. Results of the microstructure study and testing of shear strength enabled us to conclude that TiC-based cermets (TiC-FeCr and TiC-NiMo) can be successfully brazed under ambient atmosphere using filler metals and fluxes developed for WC-based cemented carbides. The shear strength of joints over 200 MPa can be achieved. Under similar brazing conditions, TiC-FeCr/steel joints compare favourably with TiC-NiMo/steel joints in terms of shear strength. The shear strength of TiC cermet/steel joints brazed with silver-based filler metal (Ag449) slightly increases (~13%) after prolonged heating at elevated temperature (250 °C). It was found that eddy current testing is prospective for rapid assessment of brazed joints quality with identical dimensions and chemical composition of multilayer structures. The differentiation of measurement results is the best at frequencies in the range of 10 … 100 kHz.