FGH4097和GH4079镍基高温合金的拉伸变形行为及位错组态研究

Study on the Tensile Deformation Behavior and Dislocation Configurations of FGH4097 and GH4079 Nickel-Based Superalloys

摘要:

采用粉末冶金工艺和变形工艺分别制备FGH4097和GH4079合金。结果表明，FGH4097合金的晶粒尺寸较GH4079合金的细小且均匀，前者晶粒度为6.0~6.5级，后者晶粒度为4.5~5.0级；FGH4097合金的γ′强化相尺寸均较GH4079合金粗大，且前者二次γ′相主要呈立方形，平均尺寸约为0.48 μm，而后者二次γ′相主要呈近球形，平均尺寸约为0.14 μm。对比二者拉伸性能可知，在25~750 ℃高温拉伸条件下，FGH4097合金的拉伸强度均较GH4079合金高，且塑性均明显较GH4079合金高，随着温度的升高，二者的拉伸强度和塑性差别越明显。为进一步探索FGH4097合金在不同温度拉伸过程中的高强度和高塑性变形机制，采用TEM分析手段进行拉伸断口微观组织表征。结果表明，FGH4097合金在25~650 ℃拉伸变形条件下，位错组态主要表现为γ通道内的高密度位错塞积，以及位错以超点阵层错和反相畴界形式切割γ′相主导，辅以少量连续层错切割γ′相和γ相。表明在中低温条件下合金的变形主要由位错切割γ′相所控制。随着拉伸温度升高至750~850 ℃，FGH4097合金中位错组态发生显著转变，γ′相和γ基体中大量微孪晶形成并占据主导地位，而连续层错和超点阵层错仅起次要作用。在高温条件下合金的主导变形机制由位错切割转变为微孪晶协同塑性变形机制。GH4079合金在25、650和750 ℃拉伸条件下均可观察到大量的连续层错切割γ′相和γ相，少量超点阵层错切割γ′相，以及少量微孪晶切割γ′相和γ相是其主要变形机制。

Abstract:

FGH4097 and GH4079 alloys were prepared by powder metallurgy and wrought processes, respectively. The experimental results show that the grain size of FGH4097 superalloy is smaller and has more uniform distribution compared with that of GH4079 superalloy, with the former having a grain size of approximately ASTM grade 6.0 to 6.5 and the latter having a grain size of approximately ASTM grade 4.5 to 5.0. The size of the γ′ strengthening phase in FGH4097 superalloy is larger than that in GH4079 superalloy, with secondary γ′ phase being mostly cubic and having an average size of about 0.48 μm in FGH4097 superalloy, whereas in GH4079 superalloy, the secondary γ′ phase is mainly near-spherical with an average size of about 0.14 μm. Comparing the tensile properties of the two superalloys, the results indicate that under the tensile conditions from room temperature to 750 ℃, the tensile strength of the FGH4097 superalloy is higher than that of the GH4079 superalloy, and its plasticity is also significantly superior to that of the GH4079 superalloy. As the temperature increases, the difference in tensile strength and plasticity between the two superalloys becomes more pronounced. To further explore the high strength and high plastic deformation mechanisms of FGH4097 superalloy during tensile processes at different temperatures, the microstructure of the tensile fractures was characterized by TEM. For the FGH4097 alloy under tensile deformation conditions from room temperature to 650 °C, the dislocation configurations are predominantly characterized by high-density dislocation pile-ups in the γ channels, as well as dislocations cutting the γ′ phase in the form of superlattice stacking faults and antiphase domain boundaries, supplemented by a small number of continuous stacking faults cutting the γ′ and γ phases. This phenomenon indicates that the deformation of the alloy at low to medium temperatures is primarily controlled by dislocations cutting the γ′ phase. As the tensile temperature increases to 750–850 °C, the dislocation configuration in the FGH4097 alloy undergoes a significant transformation. A large number of microtwins form in the γ′ phase and γ matrix, becoming the dominant phase, while continuous stacking faults and superlattice stacking faults play only secondary roles. Under high-temperature conditions, the dominant deformation mechanism of the alloy shifts from dislocation cutting to a synergistic plastic deformation mechanism involving microtwins. For the GH4079 alloy under tensile conditions at 25, 650, and 750 °C, the phenomena of a large number of continuous stacking faults cutting the γ′ and γ phases, a small number of superlattice stacking faults cutting the γ′ phase, and a limited number of microtwins cutting the γ′ and γ phases are observed in GH4079 alloy, which are its primary deformation mechanisms.