Initial Boron Uptake and Kinetics of Transient Liquid Phase Bonding in Ni-Based Superalloys

The present work details a quantitative investigation into the braze gap width dependence on the initial boron uptake (IBU) phenomena—an event which manifests during the initial stages of brazing of boron-containing filler metals. This was accomplished using in situ cyclic DSC of both full- and half-joint TLPB couples, i.e., IN625/xBNi2/IN625 and IN625/xBNi2. All joints demonstrated a linear relationship between the isothermally solidified gap width with the square root of time which were in excellent agreement with conventional metallographic analysis methods. A conceptual model designed to quantify both the extent of isothermal solidification and IBU during TLPB in terms of the redistribution of boron as borides was implemented. The investigation demonstrated excellent agreement with microstructural and DSC results further supporting the crucial role boride formation has on the kinetics of TLPB.