DD5單晶高溫合金大間隙釬焊的組織演變與界面形成機(jī)制研究

DD5單晶高溫合金大間隙釬焊的組織演變與界面形成機(jī)制研究Microstructure evolution and interfacial formation mechanism of wide gap brazing of DD5 single crystal superalloy

采用新型Ni-Co-Cr-W-B+DD99混合粉末釬料焊接DD5單晶高溫合金, 分析釬料成分對接頭顯微組織演變和接頭力學(xué)性能的影響, 探討Ni-Co-Cr-W-B釬料/DD99合金粉的界面形成機(jī)制與接頭形成機(jī)理. 結(jié)果表明, 在釬焊過程中, Ni-Co-Cr-W-B釬料/DD99合金粉的界面上首先形成了γ-Ni初生相, B偏析并析出細(xì)小顆粒狀的 M3B2 型硼化物, 在冷卻過程中殘余液相形成塊狀 M3B2相、γ+γ′共晶相和 γ-Ni+Ni3B+CrB 共晶相. 提高混合粉末釬料中 DD99 合金粉的配比, 可有效抑制焊縫中的硼化物和低熔點(diǎn)共晶相的形成, 提高焊縫成分和組織均勻性. 當(dāng) DD99 合金粉的配比增加至 70% (質(zhì)量分?jǐn)?shù))時(shí), B 可均勻擴(kuò)散至 DD5 母材和DD99 合金粉中, 未觀察到低熔點(diǎn)共晶相, 界面處脆性化合物相顯著減少, 接頭高溫性能提高. 接頭經(jīng)過固溶處理和時(shí)效處理后, 在870 ℃的高溫拉伸性能可提高至1010 MPa, 在980 ℃, 200 MPa下的持久壽命超過100 h.

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 results in the decrease of low melting point eutectic phases and brittle compounds. The high temperature tensile properties of joint is 1010 MPa at 870 ℃ and the lasting life under 980 ℃, 200 MPa is more than 100 h.

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