一种新型Ni-Cr-Co基合金的热变形行为及其组织演变研究

Hot deformation characteristics and microstructure evolution a new-type Ni-Cr-Co based alloy

摘要:

采用Gleeble-3800热压缩实验机研究了新型Ni-Cr-Co基合金在1050~1250 ℃、0.001~1 s_^-1条件下的热变形行为,并利用EBSD探讨了变形温度和应变速率对合金组织演变和动态再结晶形核机制的影响。结果表明,流变应力随变形温度的升高而降低,而随应变速率的增大而增加。基于流变应力曲线,建立合金的Arrhenius本构方程和热加工图,得到热变形激活能为520.03 kJ/mol,最佳热加工区间为1175~1250 ℃、0.006~1 s_^-1,该区域最大功率耗散效率为45％。动态再结晶分数随变形温度的升高和应变速率的降低而增加,且动态再结晶过程形成均匀细小的等轴晶粒以及∑3孪晶界。动态再结晶形核主要以晶界“弓出”为特征的不连续动态再结晶机制主导。低温高应变速率下,持续亚晶转动诱导的连续动态再结晶作为辅助形核机制发挥作用。

Abstract:

Hot deformation characteristics of a new-type Ni-Cr-Co based alloy was investigated by isothermal compression tests under the deformation temperature range of 1050~1250 ℃ and strain rate range of 0.001~1 s_^-1. The electron backscatter diffraction (EBSD) technique was employed to investiage the microstructure evolution and nucleation mechanisms of dynamic recrystallization. The result showed that the flow stress decreases with the increasing of deformation temperature and the decreasing of strain rate. The Arrhenius constitutive equation and processing map were established based on the hot deformation data, and the hot deformation activation energy was calculated as 520.03 kJ/mol. The optimum hot working conditions were obtained in the temperature scope of 1175~1250 ℃ and the strain rate range of 0.006~1 s_^-1 with the peak power dissipation efficiency of 45%. The fraction of dynamic recrystallization increases with the increasing of deformation temperature and the decreasing of strain rate. And during dynamic recrystallization, a large number of deformed grains were replaced by fine dynamic recrystallized grains and a high frequency of ∑3 twin boundaries were generated. The dominant dynamic recrystallization nucleation mechanism is grain boundary bulging, which is a typical feature of discontinuous dynamic recrystallization. In the low temperature and high strain rate region, continuous dynamic recrystallization characterized by the rotation of subgrains was detected. However, continuous dynamic recrystallization was just an assistant nucleation mechanism for the alloy.