Effect of mechanical properties using different filler metals on wide-clearance activated-diffusion-brazed Ni-based superalloy

The investigation of mechanical properties and failure mechanism of activat ed-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys N icrobraz 150 and DF4B, The microstructural characterization showed that chr omium borides with a blocky morphology were present in joints associated wi th the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phas e was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (gamma) phase and an absence of a nickel boride matrix phase, Results of t ensile test showed that ADB specimens using DF4B brazing alloy exhibited 95 % nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area mere initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor ten sile properties at all testing temperatures, and their fractures were initi ated at a brittle nickel boride site and propagated along the weak-bonded i nterface between the Ni-B eutectic phase and base materials.