燃机叶片组织与性能退化规律及恢复工艺研究

Study on Degradation Mechanisms and Rejuvenation Processes for Microstructure and Properties of Gas Turbine Blades

摘要:

研究了服役后GTD111 DS叶片显微组织和力学性能退化行为，并采用热等静压+固溶+两次时效的热处理工艺恢复。结果表明：服役后，叶尖至叶根显微疏松与孔洞增多，MC相退化为M23C6相和η相，二次γ′相球化和筏化，三次γ′相部分回熔。叶片显微组织退化规律为：叶尖＞叶身＞叶根＞榫头，同截面上排气边＞进气边＞叶背＞叶盆。组织退化导致室温与980 ℃抗拉强度、980 ℃/220 MPa持久性能从榫头至叶尖逐步降低。经恢复热处理，叶尖显微组织与性能得到明显改善，叶尖显微疏松占比降低，碳化物部分恢复，二次与三次γ′相分别减小至0.5 μm和59 nm；叶尖室温抗拉强度由810 MPa增至1122 MPa，980 ℃抗拉强度由388 MPa增至468 MPa，980 ℃/220 MPa持久寿命由1.95 h增至11.31 h，各项力学性能均高于同状态榫头区域。

Abstract:

The degradation behavior of the microstructure and mechanical properties of a long time serviced GTD111 DS superalloy turbine blade was investigated. Rejuvenation heat treatment was subsequently applied by using a treatment of hot isostatic pressing (HIP) followed by solution and double-aging treatments. The results demonstrated that during service: pore density increased significantly from blade tip to root; MC carbides degenerated into M??C? carbides and η phase; secondary γ′ precipitates underwent severe spheroidization and rafting, accompanied by the dissolution of tertiary γ′ precipitates. The overall microstructural degradation pattern along the blade longitudinal axis follows the order: tip > central region > root > tenon, and along the transverse axis follows the order: trailing edge > leading edge > suction side > pressure side. The microstructure degradation directly led to a progressive reduction in Ultimate tensile strength at both room temperature and 980 °C and stress rupture life at 980 °C/220 MPa from the tenon to the blade tip. After rejuvenation heat treatment, the microstructure and mechanical properties were markedly improved: the area fraction of microporosity at the blade tip was reduced, MC carbides were partially restored, and the sizes of secondary and tertiary γ′ precipitates decreased to approximately 0.5 μm and 59 nm, respectively. Ultimate tensile strength of the blade tip increased from 810 MPa to 1122 MPa at room temperature and from 388 MPa to 468 MPa at 980 °C; and the stress rupture life (980 °C/220 MPa) increased from 1.95 h to 11.31 h. After rejuvenation, all mechanical properties at the blade tip exceeded those of the tenon region.