Microstructure and properties of dissimilar high-temperature alloy joints (GH648/K42) brazed with BNi68CrWB filler metal

Dissimilar high-temperature alloys (K24 and GH648) were joined by using BNi68CrWB filler metal. Influence of brazing temperature, holding time and fit-up gap on microstructure and properties of joints were studied. It indicated that three typical microstructure areas were observed in the joints, e.g. eutectic area, isothermal solidification area and diffusion area. When brazing temperature was too high, the counts of W-Cr-Ni phase increased and then the mechanical properties decreased. Prolonging the holding time promoted the diffusion between brazing filler metal and matrix, and did benefit to obtain uniform solid-solution, and consequently the strength of joints increased. However, overlong holding caused the strength of joints decreased. The fit-up gap had little influence on the joints. Maximum strength value could be reached for the joints with fir-up gap of 0.05~0.10 mm brazed at 1 150℃ for 30 min.