GH4720Li合金双重晶粒组织对高温拉伸性能的影响规律

Influence rule of dual grain micstructure on high temperature tensile properties of GH4720Li alloy

摘要:

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650oC高温拉伸性能,建立了混晶组织与高温拉伸强度的量化关系,揭示了混晶对高温拉伸性能的影响机制。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650oC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,双重晶粒组织高温拉伸性能越差。

Abstract:

Mixed grain micstructures of GH4720Li superalloy with different coarse and fine grain ratios were prepared by forging deformation. The high-temperature tensile properties of different mixed grain micstructures at 650oC were tested. The quantitative relationship between mixed grain micstructures and high-temperature tensile strength was established, and the mechanism of influence of mixed grain structures on high-temperature tensile properties was revealed. The results show that the primary γ" 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 primary γ" phase distribution is, the easier it is to form the mixed grain micstructure after the deformation of the coarse grain structures. During the 650oC tensile process, the coarse grain size and volume fraction in the mixed grain micstructures significantly affect the tensile properties. With the increase of 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 micstructure, the fewer RD//<111> oriented grains are formed, the greater the dislocation slip obstruction, and the worse the high-temperature tensile property of the mixed grain micstructure.