镍基变形高温合金动态软化行为与组织演变规律研究

Dynamic Softening Behavior and Microstructure Evolution of Nickel Base Superalloy

采用Gleeble3500D热模拟试验机研究了GH4720Li合金的高温热变形行为,分析了不同热压缩工艺条件下流变力学曲线特征,建立了表征材料流变力学特征的包含应变参量的双曲正弦型Arrhenius本构关系模型以及BP人工神经网络模型,并通过对材料热变形组织的表征,揭示了GH4720Li合金高温变形过程中的动态再结晶形核机制。结果表明,包含应变参量的双曲正弦型Arrhenius本构关系模型预测精度较差,而BP人工神经网络模型能很好地表征GH4720Li合金热变形过程中的流变力学行为,模型预测值与实验值的平均相对误差仅为0.814%。组织分析结果表明,GH4720Li合金在1140℃条件下动态再结晶的主要形核机制为非连续动态再结晶,变形晶粒的晶界为再结晶晶粒提供形核位置。

Ni-based supperalloys are widely applied in manufacturing of compressor and turbine discs and polycrystal turbine blades in the hot section of aero-engines, since they possessed excellent mechanical strength and creep resistance at high temperatures. Generally, hot working is an effective way for shaping metals and alloys. Lots of typical metallurgical behaviors occurred, which were related to the hot working parameters, including deformation temperature, strain rate and strain. And BP-ANN （artifi- cial neural network based on the error-back propagation） as well as Arrhenius types models were the two of most acknowledged constitutive models to determine the relationship between the flow behavior and hot deformation parameters of various metals and alloys, at present. In order to investigate the relation- ship between deformation parameters and flow stress behavior, and precisely simulate the flow behavior during hot deformation processes of GH4720Li alloy, the hot compressive tests of GH4720Li alloy were conducted at the deformation temperature range of 1060-1140 ~C and strain rate range of 0.001-1 s-1 on Gleeble 3500D thermal simulation testing machine in this work. The relationship between microstructureand hot deformation conditions was identified. The influence of hot processing parameters on flow stress behavior was analyzed. The temperature sensitivity of the flow stress decreased with increasing tempera- ture at a strain rate of 0.1 s-1. The peak stress increased 23 MPa when the deformation temperature de- creased from 1100 ~C to 1080 ~C, only increased 7 MPa when decreased from 1140 ~C to 1120 ~C. In ad- dition, the Arrhenius model as well as BP artificial neural network model was established according to the true stress-strain curves. It shows that the established BP artificial neural network model can well exhibit the flow stress behavior of GH4720Li alloy compared with the Arrhenius model during hot deformation. The correlation coefficient between experimental findings and predicted flow stress determined by ANN model and Arrhenius model is 0.998 and 0.949, respectively. In addition, the dynamic recrystallization mechanism of the studied alloy was identified according to the deformed microstructure. Microstructure observation of the samples deformed at 1140 ~C indicated that the discontinuous dynamic recrystalliza- tion was the main nucleation mechanism and newly grain nuclei distributed along the deformed grain boundaries. The dynamic recrystallization grain size of GH4720Li alloy decreases with the increase of strain rate when the samples deformed at 1140 ~C and a strain of 0.8.