高温合金NiCr22Mo9Nb的热塑性行为与加工图研究

采用先进的热力模拟技术对高温合金NiCr22Mo9Nb合金进行热压缩试验,系统研究了合金在900～1100 ℃,0.01～5.00s-1变形条件下的热塑性行为.根据热压缩实验数据,给出不同变形参数下该合金的流变应力曲线.考虑绝热温升效应对流变应力曲线的影响,通过外推法对高应变速率曲线进行绝热温升修正,基于修正后的流变应...

Thermoplastic Behavior and Processing Map of Superalloy NiCr22Mo9Nb

As a typical superalloy,NiCr22Mo9Nb was widely used in aviation and electric power fields.Large amount of alloying elements contained in NiCr22Mo9Nb would increase the deformation resistance of the alloy,resulting in difficulty of thermal processing.Therefore,it was necessary to study the thermal processing performance of NiCr22Mo9Nb.The current research on the thermal processing of NiCr22Mo9Nb did not consider the influence of the adiabatic temperature rise effect on the flow curves at high strain rates,which would affect the accuracy of the constructed constitutive equation and hot processing map.So,it was necessary to use the extrapolation method to modify the flow stress curves,and use the modified results to study the hot processing behavior at high strain rates,which could provide the guidance for the production of NiCr22Mo9Nb workpieces.Using Gleeble-3500 simulator,thermal compression experiments of NiCr22Mo9Nb were carried out under deformation conditions of 0.01~5.00 s^-1 and 900~1100℃.The samples were processed into cylinders ofΦ8 mm×12 mm.According to the thermal compression experiment data,the flow stress curves of the alloy under different deformation parameters were calculated.Considering the influence of adiabatic temperature rise effect,the correction was carried out by extrapolation method on the curves with high strain rate.The Arrhenius constitutive model was constructed based on the corrected flow stress curves.According to the theory of dynamic material model,hot processing maps of the alloy under different strains were derived.Combined with the microstructure,the deformation behavior of the NiCr22Mo9Nb was analyzed.The results showed that:(1)When the NiCr22Mo9Nb alloy was deformed at a high strain rate,an obvious adiabatic temperature rise occurred with the increase of the true strain.Under different deformation parameters,the stress after correction by the extrapolation method increased to different levels obviously.(2)According to the revised stress data,the material constantsα,n,A and the thermal deformation activation energy Q(kJ·mol^-1)of NiCr22Mo9 Nb alloy were calculated,and the constitutive equation of NiCr22Mo9Nb alloy was constructed.Then the relationship between true stress,deformation temperature and strain rate were established.(3)The hot processing maps of NiCr22Mo9Nb alloy were constructed based on the theory of the dynamic material model.It was found that there was a peakηregion under 1090℃-1×10-0.6 s^-1.At the same time,a large area of instability under strain rate near 1×10-0.5~1×100.25 s^-1.By calculating the relationship between theηvalue and the strain variable under different deformation parameters,it was found that when the strain rate was 5.00 s^-1,theηvalue decreased with the increase of the strain variable.(4)Combined with the microstructure analysis,it was found that when the deformation condition was 1050℃-5 s^-1,dynamic recrystallization occurred.But the dynamic recrystallization phenomenon was insufficient due to the high strain rate.While in the instability zone(950℃-1 s^-1),incomplete dynamic recrystallization occurred with a"necklace structure".When the deformation parameter was 1050℃-0.1 s^-1,the microstructure showed a complete dynamic recrystallization characteristic.The study came to the following conclusions:the flow stress curves of NiCr22Mo9Nb alloy presented dynamic recrystallization characteristic obviously.Distinct adiabatic temperature rise phenomenon occurred at a higher strain rate(5.00 s^-1),which phenomenon weakened as the increase of deformation temperature.The thermal deformation activation energy was 485.31 kJ·mol^-1 at 900~1100℃.Combined with the hot processing maps and the microstructures,the instability zone was among deformation temperature(T)=900~1100℃,the strain rates(ε)=0.3~1.8 s^-1.The complete recrystallization area of the alloy was detected under 1050~1100℃and 0.10~0.25 s^-1,which was recommended the best hot processing window of this NiCr22Mo9Nb alloy.