Effect of gap size and process parameters on diffusion brazing of Inconel 738

The influence of gap size and brazing parameters (temperature and time), on the microstructure and properties of diffusion-brazed Inconel 738 (IN-738) superalloy, was investigated using two commercial brazing alloys, Amdry 'DF3' and Nicrobraz 150. The residual liquid present at brazing temperature was observed to transform on cooling into centreline eutectic constituents in 'NB 150' brazement while three different dispersed intermetallic phases were observed in the 'DF3' joint. The volume fraction of the second phases increased with gap size in both 'NB 150' and 'DF3' brazements. In addition to the centreline eutectic constituents, nickel and chromium rich borides were observed at the melt back zone in samples brazed below the Ni 3 B eutectic temperature of 1093°C, and above this temperature only chromium rich borides were observed. Joints containing the second phase intermetallics in 'NB 150' and 'DF3' brazed materials were found to exhibit tensile properties inferior to that of the base alloy.