High temperature brazing processes using nickel base filler alloys produce oxidation and corrosion resistant high strength joints suitable for high temperature applications. However, boron and silicon that are used as melting point depressants in these filler alloys form eutectic structures that are extremely hard and contain very brittle intermetallic compounds. It is therefore of interest to control and engineer the microstructures of the brazed joints which have minimal weaknesses arising from the formation of these intermetallic compounds.

 

Computational thermodynamics is applied to the high temperature brazing of SS 321 with BNi-2 to understand the evolution of microstructures, phase stability, solidification behavior, micro-segregation effects, and phase transformation behavior. Using solidification simulation and thermodynamic modeling of multi-component phase equilibria, the effects of process parameters resulting in brittle phases are presented. This in turn would lead to the optimization of the process variables such as brazing temperature, holding time and joint gap. Experimental Investigations were carried out in the range of 1325-1394K brazing temperatures with 10-90 minutes holding time to obtain the dissolution data of base metal and to verify the thermodynamic model. SEM and EDS analyses were used to identify the phases. The maximum brazing clearances (MBC) were also determined experimentally for the above mentioned combination.