Effect of pre-deoxygenation treatment on the properties of BNi-7 brazing filler metals and its brazed joints

Abstract

The oxidation that occurs during the production and storage of brazing filler metals serves as the primary cause of metallurgical defects in the brazed joints. To investigate the role of oxygen concentration in the coupling relationship between the microstructure and mechanical properties of both the filler metal and the brazed joint, this study implemented a TiH₂ precursor pre-deoxygenation process on gas-atomized BNi-7 brazing alloy. The oxygen concentration exhibited a characteristic parabolic variation with increasing pre-deoxygenation temperature, reaching a minimum value of 0.060 wt % at 500 °C and 23.08 % reduction compared to the original powder. At the optimized oxygen content of 0.060 wt %, the liquidus temperature of the brazing alloy significantly decreased to 890 °C, with a narrowed melting range of 6.2 °C. The microstructure of the brazed joints displayed typical eutectic morphology characteristics, which consist of a continuously distributed Cr/Fe-enriched Ni solid solution matrix; a Cr-segregated Ni₃P-Ni(Cr) intermetallic compound in the central region and discretely distributed Ni(Cr, Fe)-P metastable phases. Under optimal oxygen conditions (0.06 wt %), the maximum shear strength reached 57 MPa, reflecting a 15 % strength improvement over the baseline group. The results indicate that oxygen reduction effectively suppresses heterogeneous nucleation processes and enhances metallurgical homogenization.