BNi68CrWB钎焊K24/GH648异种高温合金的界面形成机理

采用BNi68CrWB钎料粉末对K24和GH648异种高温合金进行钎焊连接，分析了接头典型界面组织，提出了钎焊过程反应机理.结果表明，接头由共晶区、等温凝固区和扩散区组成.共晶区由WB，CrB和镍基固溶体组成，等温凝固区为镍基固溶体，GH648侧扩散区由WB，W_xB_y，Cr_xB_y，以及沿晶界析出的镍基固溶体和少量的Cr₂Ni₃相组成，K24侧扩散区与母材差异不明显.钎焊过程由元素富集、母材溶解、等温凝固和共晶凝固四个阶段组成.其中等温凝固阶段是钎焊过程中最关键的阶段，等温凝固不完全时，钎缝中央存在共晶组织，影响接头性能.钎焊温度1 150℃，保温120 min时，等温凝固完全，接头组织均匀，力学性能最优，室温拉剪强度可达323 MPa.

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.