一种新型镍基高温合金的动态再结晶行为

Dynamic Recrystallization Behavior of a Novel Ni-based Superalloy

摘要:

采用等温热压缩实验研究了一种新型镍基高温合金在不同热变形条件下（变形温度1040~1120 ℃、应变量0.35~1.2、应变速率0.1 s^-1）的动态再结晶行为。通过光学显微镜（OM）、扫描电子显微镜（SEM）和电子背散射衍射仪（EBSD）研究变形温度和应变量对合金热变形过程中组织演变和动态再结晶（DRX）形核机制的影响。结果表明，根据加工硬化率曲线能够准确确定DRX出现的临界应力和临界应变。合金的DRX晶粒体积分数随变形温度和应变量的增加而增加。在高温低应变速率下，不连续动态再结晶（DDRX）和连续动态再结晶（CDRX）形核机制同时发生。随着变形温度的升高，CDRX形核机制减弱，而CDRX机制在高温条件下占据主导。随着应变量的增加，合金中DDRX机制逐渐变强。热变形后期，CDRX仅作为辅助形核机制发挥作用。另外，Σ3孪晶界的形成有助于DRX晶粒的形核。

Abstract:

The dynamic recrystallization behavior of a novel Ni-based superalloy was investigated by means of isothermal compression tests in the temperature range of 1040?1120 °C, and the strain range of 0.35?1.2 with a strain rate of 0.1 s^-1. The microstructure evolution and nucleation mechanism of dynamic recrystallization (DRX) were investigated by optical microscope (OM), scanning electrical microscope (SEM), and electron backscattered diffraction (EBSD). Results show that the critical stress and strain for the initiation of DRX are determined from the work hardening rate curves. The volume fraction of DRX grains increases with increasing the temperature and strain. Both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexist at low deformation temperature and low strain. The effect of CDRX becomes weaker with increasing the deformation temperature, and DDRX is the dominant nucleation mechanisms of DRX at higher temperatures. With increasing strain, the effect of DDRX becomes stronger, and CDRX can only be considered as an assistant nucleation mechanism of DRX at the latter stage of deformation for the studied superalloy. Additionally, Σ3 twin boundary contributes to the nucleation of DRX grains.