Assessing the Influence of Cr and Fe in the Filler Metal on Dissolution and Isothermal Solidification Kinetics During TLPB of Ni-Based Superalloys

The influence of chromium and iron’s absence (BNi-3) and presence (BNi-2) in boron-containing filler metals (FM) on the TLPB behavior of IN718 base metal (BM) was examined. Results indicate that the absence of Cr and Fe in the FM significantly aggravated BM dissolution and gap widening, particularly when similar degrees of brazing beyond the FM liquidus temperature occurred. This led to a higher complete isothermal solidification time, despite a higher rate of isothermal solidification (IS) and initial boron uptake displayed by the IN718/BNi-3 joint. EDS and quantitative image analysis performed within the DAZ concluded that differences observed in the rate of IS were related to the amount and type of borides forming in the DAZ. The lack of Cr in the BNi-3 favored the formation of Cr-poor:B-rich Cr(Mo,Nb)B borides, leading to a higher rate of B uptake by the base metal. Joints made from the Cr containing BNi-2 FM displayed a combination of Cr-rich:B-poor CrB and Cr(Mo,Nb)B borides leading to lower rates of B uptake.