Abstract
During the past two decades, the high-entropy alloy AlCoCrFeNi has attracted much attention due to its outstanding thermal and mechanical properties under ambient conditions. However, the exploration on the thermodynamic properties of this alloy under high temperatures and high pressures is relatively insufficient. Combining structural modeling with the similar atomic environment (SAE) method and first-principles simulations with the modified mean-field potential (MMFP) approach, we studied the lattice and magnetic structure as well as the thermodynamic properties of the body-centered-cubic AlCoCrFeNi, through supercell simulations. AlCoCrFeNi was found to display a strong local lattice distortion compared with typical 3d high-entropy alloys; the ferromagnetic structure stable at 0 K was predicted to transform to the paramagnetic structure at the Curie temperature TC = 279.75 K, in good agreement with previous calculations; the calculated equilibrium volumes, bulk modulus, and shock Hugoniot all agree well with available experimental data and other theoretical values. These results demonstrate the validity and reliability of our methods used to study the dynamic properties of AlCoCrFeNi, providing a promising scheme for accessing the dynamic properties of sophisticated high-entropy alloys.
Highlights
High-entropy alloys (HEAs) or multi-principle–element alloys represent a special group of solid solutions containing five or more elements, where the concentration He et al, 2018, Korchuganov, 2018, Li et al, 2018 of each element is between 5 and 35 at. % (Cantor et al, 2004; Yeh et al, 2004; Zhang et al, 2014)
Since local lattice distortions can be strong in HEAs (Song et al, 2017), for the bcc AlCoCrFeNi, the supercell approach should be more appropriate than the conventional coherent potential approximation (CPA) (Gyorffy, 1972)
The difference is 0.04 Å3/atom between the volume V0 calculated by mean-field potential (MFP) and that given in the X-ray diffraction (XRD) experiment by Cheng et al (2019)
Summary
High-entropy alloys (HEAs) or multi-principle–element alloys represent a special group of solid solutions containing five or more elements, where the concentration He et al, 2018, Korchuganov, 2018, Li et al, 2018 of each element is between 5 and 35 at. % (Cantor et al, 2004; Yeh et al, 2004; Zhang et al, 2014). According to Wang et al (2012), when x < 0.5, AlxCoCrFeNi possesses the face-centered cubic (fcc) structure; when x > 0.9, AlxCoCrFeNi has the body-centered cubic (bcc) structure (with a chemically ordered B2 or disordered A2 structure); when 0.5 < x < 0.9, the crystal structure of AlxCoCrFeNi is a mixture of fcc and bcc (A2 or B2). These results indicate that the addition of the element Al tends to stabilize the bcc structure. It is worth noting that, CoCrFeNi (equivalently AlxCoCrFeNi with x 0) is paramagnetic at ambient conditions, while Al2CoCrFeNi (AlxCoCrFeNi with x 2) becomes paramagnetic at a higher Curie temperature of around 430 ± 3 K (Tian et al, 2013)
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