服役透平叶片GTD111 DS合金再热恢复研究

Re-heat rejuvenation study of directionally solidified GTD111 DS superalloy in service damaged gas turbine blades

以服役透平叶片GTD111 DS定向合金材料为研究对象,采用光学显微镜和扫描电镜对简单再热恢复处理前后的叶片材料微观组织进行观察,并对合金材料显微硬度进行测试,研究再热恢复参数对γ'相(主要沉淀强化相)特征的影响规律,评估恢复态叶片材料的组织和性能.结果表明:固溶温度、冷却速度、时效温度和时间是再热恢复处理的关键参数;合适温度下的固溶处理可有效溶解粗大形变γ'相,并重新析出细小均匀的二次γ'相,同时避免初熔和再结晶;两级时效处理可优化双尺寸形态γ'相的尺寸、体积分数和立方度.恢复处理后叶片不同部位的组织和性能分布更加均匀,二次γ'相和三次γ'相的平均颗粒尺寸分别约为440和70nm,其体积分数分别约为35%和3%,硬度值处于409～417 HV范围内,高于叶根部位原始状态的硬度值.

Microstructure and microhardness of directionally solidified GTD111 DS superalloy after service exposure and different simple re-heat rejuvenation treatment for turbine blades were studied by light optical microscope,scanning electron microscopy(SEM),and vicker microhardness tester,respectively.Then the effect of rejuvenation conditions on microstructure characteristics of the precipitation strengthening phaseγ’of directionally solidified superalloy in turbine blades was investigated,and the microstructure and properties of the rejuvenated blades material were evaluated.The results show that solution temperature,cooling rate,aging temperature and time are most important rejuvenation parameters of turbine blades.The solution treatment under proper temperature condition can dissolve effectively coarsened and deformedγ’phase,and re-precipitate fine secondaryγ’phase,with initial melting and recrystallization avoided.Two-stage aging can optimize the size,volume fraction and cubic degree of the bimodal sizeγ’phase with coarse secondaryγ’phase and fine tertiaryγ’phase.After re-heat rejuvenation treatment,the microstructure of blades material becomes finer and more homogeneous,and material properties distribute more uniform.For different locations of the rejuvenated blades,the sizes of secondaryγ’phase and tertiaryγ’phase are about 440 and 70 nm,the volume fractions of secondaryγ’phase and tertiaryγ’phase are about 35%and 3%,and the microhardness values are all in range of 409~417 HV,which are even higher than that of virgin station in blades root.