A review of hot deformation behavior and constitutive models to predict flow stress of high-entropy alloys

The dynamic recrystallization as well as meta‐dynamic and static recrystallization of the nickel‐based alloy 80A was investigated by means of electron backscatter diffraction (EBSD). Specimens were hot compressed at a temperature of 1120°C and a strain rate of 0.1/s at varying strain and soak times to describe the recrystallization behaviour. Various approaches were tested in order to differentiate between recrystallized and deformed grains based on EBSD data. The grain orientation spread was clearly found to be the most reliable procedure. A high twinning of the recrystallized grains was observed, and as a consequence the measured grain size was strongly dependent on whether the coherent and incoherent twin boundaries were regarded as genuine boundaries or removed.

Recrystallization behaviour of the nickel based alloy 80A during hot forming

A perspective on precipitation-hardening high-entropy alloys fabricated by additive manufacturing

Refractory high-entropy alloys (RHEAs) with excellent comprehensive mechanical properties at high temperature are a new research focus in the field of materials. In this paper, the compositional design theory and the simulation research based on first-principles of density functional theory (DFT) for RHEAs were introduced. The research status of compositional optimization, doping non-metallic elements and functional phases, and phase structure regulation for RHEAs were summarized. In addition, the process characteristics of smelting, powder metallurgy, magnetron sputtering and laser cladding were reviewed, and the feasibility and difficulties of preparing RHEAs by extreme high-speed laser cladding (EHLC) were analyzed. Finally, the following suggestions were put forward for the development direction of RHEAs: improving the theory and simulation study of RHEAs composition design, investigating the strengthening effect of doping non-metallic elements and functional phases in RHEAs, paying attention to the synergistic effect between different phase structures, optimizing the process of preparing RHEAs by laser cladding to realize direct forming of parts, and expanding the application of EHLC in preparation of RHEAs coatings. 

Composition design and preparation process of refractory high-entropy alloys: A review

Study on the dynamic recrystallization mechanisms of GH5188 superalloy during hot compression deformation

Unique hot deformation behavior and microstructure evolution of a dual FCC-phase CoCrCu1.2FeNi high entropy alloy

Recrystallization process of hot-extruded 6A02 aluminum alloy in solid and semi-solid temperature ranges

High temperature and short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state

In this paper, nickel-based superalloy disk parts were fabricated by semi-solid thixoforming, and some of them were subjected to standard heat treatment High temperature creep properties of the thixoformed parts before and after heat treatment were studied The effects of temperature and stress on the microstructure and steady state creep rate were investigated The results exhibited that heat treatment had a positive influence on the initial microstructure and creep properties of the thixoformed parts The creep life and creep strain of the specimen without heat treatment at 850 °C/196 MPa were 283 h and 33%, respectively After heat treatment, the creep life and creep strain of the specimen increased to 527 h and 99%, respectively The steady state creep rate increased with the increase of temperature and stress The microstructure observations indicated that the creep process had little effect on the morphologies and compositions of the grain boundary carbides, while it promoted the growth of the γ′ precipitates With the increase of temperature and stress, the average diameter of γ′ precipitates increased At 850 °C/196 MPa, the dislocations tended to pass the γ′ precipitates through Orowan looping mechanism The creep fracture of the specimen without heat treatment was mainly intergranular fracture, while the transgranular fracture was dominant after heat treatment

High temperature creep behavior of thixoformed nickel-based superalloy parts

In this work, the effect of heat treatment on the microstructure and high temperature mechanical properties of the GH4037 cylindrical parts fabricated via thixoforming was investigated. The microstructure of the thixoformed GH4037 parts before heat treatment was composed of solid grains and eutectic phases, while it mainly consisted of equiaxial grains after heat treatment. After heat treatment, a large number of spherical γ′ precipitates dispersed inside the grains, while primary γ′ particles, streaks of M23C6 carbides and blocks of MC carbides precipitated along the grain boundaries. When the tensile test temperature increased from room temperature to 1000 °C, the tensile strength of GH4037 alloy decreased gradually, while the elongation presented a trend of descending first and then ascending. After heat treatment, the tensile strength realized a remarkable improvement while the elongation was inevitably reduced. The results indicated that the microstructure and mechanical properties of the thixoformed GH4037 parts were significantly improved by heat treatment, and verified the feasibility of thixoforming in the field of nickel-based superalloys.

Minjie Huang

Papers

Unique hot deformation behavior and microstructure evolution of a dual FCC-phase CoCrCu1.2FeNi high entropy alloy

Recrystallization process of hot-extruded 6A02 aluminum alloy in solid and semi-solid temperature ranges

High temperature and short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state

High temperature creep behavior of thixoformed nickel-based superalloy parts

Microstructure and mechanical properties of thixoformed GH4037 parts before and after heat treatment