Welding Metallurgy of

As human improve their ability to fabricate materials, alloys have evolved from simple to complex compositions, accordingly improving functions and performances, promoting the advancements of human civilization. In recent years, high-entropy alloys (HEAs) have attracted tremendous attention in various fields. With multiple principal components, they inherently possess unique microstructures and many impressive properties, such as high strength and hardness, excellent corrosion resistance, thermal stability, fatigue, fracture, and irradiation resistance, in terms of which they overwhelm the traditional alloys. All these properties have endowed HEAs with many promising potential applications. An in-depth understanding of the essence of HEAs is important to further developing numerous HEAs with better properties and performance in the future. In this paper, we review the recent development of HEAs, and summarize their preparation methods, composition design, phase formation and microstructures, various properties, and modeling and simulation calculations. In addition, the future trends and prospects of HEAs are put forward.

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Science and technology in high-entropy alloys

A review on fundamental of high entropy alloys with promising high–temperature properties

ASME boiler and pressure vessel codeの許容応力の改訂

Mechanical behavior of high-entropy alloys

Effect of C content on microstructure and tensile properties of as-cast CoCrFeMnNi high entropy alloy

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

Cooling rate effect on microstructure and mechanical properties of AlxCoCrFeNi high entropy alloys

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.

Zhihao Yao

Papers

Effect of C content on microstructure and tensile properties of as-cast CoCrFeMnNi high entropy alloy

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

Cooling rate effect on microstructure and mechanical properties of AlxCoCrFeNi high entropy alloys

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