비만아 부모의 돌봄 경험: q 방법론

EBSD analysis of evolution of dynamic recrystallization grains and δ phase in a nickel-based superalloy during hot compressive deformation

The hot deformation behavior of an IN718 superalloy was studied by isothermal compression tests under the deformation temperature range of 950–1100 °C and strain rate range of 0.001–1 s−1 up to true strains of 0.05, 0.2, 0.4 and 0.7. Electron backscattered diffraction (EBSD) technique was employed to investigate systematically the effects of strain, strain rate and deformation temperature on the subgrain structures, local and cumulative misorientations and twinning phenomena. The results showed that the occurrence of dynamic recrystallization (DRX) is promoted by increasing strain and deformation temperature and decreasing strain rate. The microstructural changes showed that discontinuous dynamic recrystallization (DDRX), characterized by grain boundary bulging, is the dominant nucleation mechanism in the early stages of deformation in which DRX nucleation occurs by twining behind the bulged areas. Twin boundaries of nuclei lost their ∑3 character with further deformation. However, many simple and multiple twins can be also regenerated during the growth of grains. The results showed that continuous dynamic recrystallization (CDRX) is promoted at higher strains and large strain rates, and lower temperatures, indicating that under certain conditions both DDRX and CDRX can occur simultaneously during the hot deformation of IN718.

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Dynamic recrystallization mechanisms and twining evolution during hot deformation of Inconel 718

Microstructural evolution and constitutive models to predict hot deformation behaviors of a nickel-based superalloy

Strain rate dependent microstructural evolution during hot deformation of a hot isostatically processed nickel base superalloy

Hot deformation characteristics of Alloy 617B nickel-based superalloy: A study using processing map

Substructure and twin boundary evolution of alloy 617B during dynamic recrystallization (DRX) was investigated by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) technique. Simulated compression tests were carried out at different true strains in the temperature range of 1120–1210 °C with a strain rate of 0.001 s −1 . The results show that discontinuous dynamic recrystallization (DDRX) featured by original grain boundary bulging is the dominant nucleation mechanism for alloy 617B. The progressive subgrain rotation, which is a characterization of continuous dynamic recrystallization (CDRX) can be detected at the early stage of hot deformation at lower temperature, which can just be considered as an assistant mechanism. The evolution of substructure and twin boundaries have a significant effect on DRX process of alloy 617B. Twinning formation can active the DRX process by accelerating original grain boundary bulging and separation of bulging grain boundaries. The formation of twin steps resulting from twin slipping provide additional DRX nucleation locations. The effort of twins gets weaker with the increase of temperature as the DRX grain growth process associated with grain boundary area reduction gradually becomes a preferential mechanism for energy minimization. Different from previous study, the fraction of twin boundaries decrease with the increase of temperature, which can be attributed to the twin boundary accelerated prior grain growth process. Such process also results in the serious bulging of grain boundaries into adjacent grains.

Evolution of twins and substructures during low strain rate hot deformation and contribution to dynamic recrystallization in alloy 617B

The effect of strain rate on dynamic recrystallization (DRX) behavior and mechanism of alloy 617B was investigated by isothermal compression test in a temperature range of 1393 K to 1483 K (1120 °C to 1210 °C) with a wide strain rate scope of 0.01 to 20 s−1. The microstructure evolution was investigated comprehensively by optical microscopy, electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM) to provide detailed insight into the effect of strain rate on DRX mechanism. The study shows that DRX is accelerated at both low strain rate and high strain rate conditions with an apparent sluggish kinetics at the intermediate strain rate of 1 s−1. In the low strain rate condition (i.e., <1 s−1), DRX is mainly controlled by the growth of DRX nuclei due to the sufficient time. When the strain rate is higher than 1 s−1, besides the commonly accepted reason of adiabatic heat generated by high strain rate, enhanced DRX nucleation mechanism is crucial for the promotion of DRX at high strain rate. High strain rate could lead to enhanced pile-up of dislocation and higher stored energy, which can facilitate the process of DRX. In addition, distortion or subdivision of twins and “grain fragment” are detected when the strain rate is higher than 1 s−1, which provide additional DRX nucleation mechanism. As a result, the combined effect leads to the higher DRX nucleation rate to promote DRX at high strain rate. The effect of strain rate on DRX is the completion result between sufficiency of time on the one hand and adiabatic heat and enhanced nucleation mechanism on the other.

He Jiang

Papers

Hot deformation characteristics of Alloy 617B nickel-based superalloy: A study using processing map

Evolution of twins and substructures during low strain rate hot deformation and contribution to dynamic recrystallization in alloy 617B

A Study on the Effect of Strain Rate on the Dynamic Recrystallization Mechanism of Alloy 617B

The recrystallization model and microstructure prediction of alloy 690 during hot deformation

Phenomenological model for the effect of strain rate on recrystallization and grain growth kinetics in the 617B alloy