Thermal Deformation Behavior of Al19.3Co15Cr15Ni50.7 High Entropy Alloy

Al(19.3)Co(15)Cr(15)Ni(50)(.7)is a eutectic high entropy alloy with a lamellar structure and good hightemperature properties. To study the thermal deformation behavior of the samples (diameter 8 mm, height 10 mm), the samples were hot compressed using the Gleeble-3500 thermal simulation-testing machine. The true stress-true strain curves were obtained for strain rates between 0.001 and 0.1 s(-1) and deformation temperatures from 973 K to 1273 K. According to the Arrhenius model, the constitutive equation of the alloy in the strain range of 0.1-0.7 is established, and the deformation activation energy and material parameters under different strain conditions were obtained. With the strain (epsilon) as the independent variable, the material constants are fitted using the sixth order polynomial, such that the material constant of a certain strain, and the constitutive equation of the strain is obtained. Finally, the constitutive equation is verified. Based on the power dissipation theory and instability criterion of the dynamic material model, the power dissipation and instability diagram are constructed, and the hot working diagram in the strain range of 0.3-0.7 for the Al19.3Co15Cr15Ni50.7 high entropy alloy is established by the superposition of the two diagrams. The results show that the flow stress curve at 1273 K presents dynamic recovery characteristics, while the flow stress curve at other temperatures presents dynamic recrystallization characteristics, and the flow stress increases with a decrease in the deformation temperature or an increase in the strain rate. The constitutive equation was established and verified, and the decision coefficient R-2 = 0.956, which was relatively high, indicates that the established flow stress constitutive model could predict the flow stress of the alloy. After high-temperature compression, compared with the as-cast microstructure, the strip-shaped B2 phase has some bending after hot deformation, and even fracture may occur under the condition of a high-strain rate. The original fine lamellar B2 phase grows into coarse lamellar, and based on the dynamic material model (DMM) theory, the stable zone and unstable zone are determined, and the optimal process parameters are determined.

Automated summary

The study investigated the thermal deformation behavior of the Al19.3Co15Cr15Ni50.7 high entropy alloy through hot compression testing, establishing a constitutive equation to reveal the flow behavior under different temperature and strain rate conditions. The flow stress curves exhibited dynamic recrystallization or dynamic recovery characteristics, with flow stress increasing as deformation temperature decreases or strain rate increases.