采用新型Ni-Co-Cr-W-B+DD99混合粉末钎料焊接DD5单晶高温合金, 分析钎料成分对接头显微组织演变和接头力学性能的影响, 探讨Ni-Co-Cr-W-B钎料/DD99合金粉的界面形成机制与接头形成机理. 结果表明, 在钎焊过程中, Ni-Co-Cr-W-B钎料/DD99合金粉的界面上首先形成了γ-Ni初生相, B偏析并析出细小颗粒状的M₃B₂ 型硼化物, 在冷却过程中残余液相形成块状M₃B₂相、γ+γ′共晶相和γ-Ni+Ni₃B+CrB共晶相. 提高混合粉末钎料中DD99合金粉的配比, 可有效抑制焊缝中的硼化物和低熔点共晶相的形成, 提高焊缝成分和组织均匀性. 当DD99合金粉的配比增加至70% (质量分数)时, B可均匀扩散至DD5母材和DD99合金粉中, 未观察到低熔点共晶相, 界面处脆性化合物相显著减少, 接头高温性能提高. 接头经过固溶处理和时效处理后, 在870 ℃的高温拉伸性能可提高至1010 MPa.

Ni-based single-crystal superalloy DD5 has excellent high temperature properties, which is the preferred raw material for aero-engine turbine blade in recent year. In this research, DD5 superalloy was brazed by different contents of Ni-Co-Cr-W-B+DD99 mixed powder filler alloy. The microstructure evolution and interfacial formation mechanism of DD5 superalloy brazing joint were analyzed by SEM and EPMA. The mechanical properties of joint after solid solution treatment and aging treatment were tested. The results show that γ-Ni primary phase formed firstly in the Ni-Co-Cr-W-B/DD99 interface during the brazing process, and then B element segregated and precipitated to fine granular M₃B₂ type boride. The residual liquid phase solidified and formed lastly to the M₃B₂ phase, γ+γ′ eutectic phase and γ-Ni+Ni₃B+CrB eutectic phase during cooling. With increasing the ratio of DD99 in mixed powder filler alloy, the low melting point eutectic phase and borides in the joint decrease and the uniformity of composition and microstructure of joint improve. When the ratio of DD99 increased to 70% (mass fraction) in the mixed powder filler alloy, it can be observed that element of B diffused to DD99 additive powder which result ed in the decrease of low melting point eutectic phases and brittle compounds. The high temperature tensile properties of joint is 1010 MPa at 870 ℃.