GH4720Li合金混晶组织对高温拉伸性能的影响规律

Influence Rule of Mixed Grain Microstructure on High-Temperature Tensile Properties of GH4720Li Alloy

通过锻造变形制备了GH4720Li高温合金不同粗细晶比例的混晶组织,测试了不同组织的650℃高温拉伸性能,建立了高温拉伸强度与混晶组织的量化关系,揭示了混晶对高温拉伸性能的影响规律与机制。结果表明:粗晶态GH4720Li合金在高温锻造变形过程中,一次γ′相分布直接影响着混晶组织演化,一次γ'相分布越不均匀,粗晶组织变形后越容易形成混晶组织;合金650℃高温拉伸过程中,混晶组织内粗细晶粒尺寸和体积分数会显著影响拉伸性能变化,随着粗晶粒尺寸和体积分数增加,合金高温拉伸强度先缓慢下降、再快速降低,而塑性则下降较快,抗拉强度与粗细晶等效晶粒尺寸呈现出Hall-Petch量化关系,但粗晶尺寸对等效晶粒尺寸的影响高于细晶;混晶组织高温拉伸变形中会形成较多的RD//<111>取向晶粒,粗细晶比例相差越小,形成的RD//<111>取向晶粒数量越少,位错滑移阻碍越大,高温拉伸性能越差。

Mixed grain microstructures of GH4720Li superalloy with different coarse and fine grain ratios were prepared by forging deformation.The high-temperature tensile properties of different mixed grain microstructures at 650℃were tested.The quantitative relationship between high-temperature tensile strength and mixed grain microstructures was established,and the influence vole of mixed grain structures on high-temperature tensile properties was revealed.The results show that the primaryγ'phase distribution directly affects the evolution of the mixed grain structures during the high-temperature forging process of coarse crystal GH4720Li alloy.The more uneven the primaryγ'phase distribution,the easier it is to form the mixed grain microstructure after the deformation of the coarse grain structures.During the 650℃tensile process,the coarse grain size and volume fraction in the mixed grain microstructures significantly affect the tensile properties.With the increase in the coarse grain size and volume fraction,the high-temperature tensile strength of the alloy decreases slowly and then rapidly,while the plasticity decreases rapidly.The tensile strength shows a Hall-Petch quantization relationship with the equivalent grain size.But the effect of coarse grain size on the equivalent grain size is higher than that of fine grain size.The RD//<111>oriented grains are formed in the microstructure during high-temperature tensile deformation.The smaller the difference in the ratio of coarse and fine grains in the mixed grain microstructure,the fewer the RD//<111>oriented grains are formed,the greater the dislocation slip obstruction,and the worse the high-temperature tensile property of the mixed grain microstructure.