Brazing mechanism of the dissimilar high-temperature alloy joints (GH648/K24)brazed with BNi68CrWB filler alloy

Dissimilar high-temperature alloys (K24 and GH648) were brazed by using BNi68CrWB brazing alloy. Typical microstructure and properties of the joints were studied. Then the reaction mechanism of the brazing process was explored. It indicated that three typical microstructure zones were observed in the joints, e.g. eutectic zone, isothermal solidification zone and diffusion zone. Eutectic zone was formed by WB, CrB and Ni-based solid solution. Isothermal solidification zone was formed by Ni-based solid solution. Diffusion zone on the GH648 side was formed by WB, WxBy, CrxBy, Ni-based solid solution and Cr₂Ni₃. Diffusion zone on the K24 side was similar to K24. The brazing process was simplified and divided into four processes: such as element enrichment process, dissolving process, isothermal solidification process and eutectic solidification process. The isothermal solidification process played a decisive role in microstructure and mechanical properties of the joint. Maximum strength value could be reached to 323 MPa when the joints were brazed at 1 150 ℃ for 120 min.