High-entropy Solid Solution Research Articles

First-Principle Studies of a High Entropy Solid Solution of AlCoCrCuFeNix with Different Mole Fractions of Ni

The structural properties, elastic properties, and heat of formation of a high entropy alloy (HEA) of AlCoCrCuFeNi containing different mole fraction of Ni. The calculated results indicate that the lattice parameter decreased and the mass density increased as the mole fraction of Ni increased. The high entropy solid solutions AlCoCrCuFeNixusing the FCC model are mechanically stable. The elastic properties have been deduced by Voigt-Reuss-Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that When the mole fraction of Ni was 0 in the FCC model, or 0.5 in both the BCC and FCC models, the high entropy solid solutions were considered ductile materials. All the HEAs are thermodynamically stable due to their negative heats of formation.

Searching for Next Single-Phase High-Entropy Alloy Compositions

There has been considerable technological interest in high-entropy alloys (HEAs) since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new single-phase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu.

Characterization of nanocrystalline CoCrFeNiTiAl high-entropy solid solution processed by mechanical alloying

The equiatomic multicomponent CoCrFeNiTiAl high-entropy solid solution alloy was synthesized by mechanical alloying (MA). The effects of milling duration and subsequent annealing on the structure and morphology evolution were investigated. Supersaturated BCC and FCC solid solutions appear when the blended powder is ball milled more than 18 h. The 30 h ball milled alloy powder shows excellent chemical homogeneity and refined morphology with mean particle size of less than 5 μm. The microscaled particles are actually hard agglomerations of nanoscaled crystallines with crystal size of about 40 nm. The phase composition transforms to two BCC solid solutions when the 30 h mechanically alloyed powder was annealed at 600 °C for 1 h. The simple solid solution structure can be maintained even after the alloy was annealed at 1000 °C. The 30 h milled alloy powder was subsequently consolidated by spark plasma sintering (SPS) at 800 °C for 10 min. The sintered sample Exhibits 98% in relative density and 432 HV in Vickers hardness.

Synthesis and characterization of nanocrystalline AlFeTiCrZnCu high entropy solid solution by mechanical alloying

Traditional alloys are based on one or two major alloying elements. High entropy alloys are equiatomic multicomponent alloys, wherein configurational entropy is maximized to obtain single phase solid solutions. The present paper reports synthesis of nanostructured equiatomic high entropy solid solutions from binary to hexanary compositions in Al–Fe–Ti–Cr–Zn–Cu system by mechanical alloying. These alloys have BCC structure with crystallite size less than 10 nm. The high entropy solid solution in these alloys is stable even after annealing at 800 °C for 1 h. The hardness of AlFeTiCrZnCu solid solution is 2 GPa in the sintered condition with a density of 99%. The similar nanostructured solid solutions have also been synthesized in CuNiCoZnAlTi and NiFeCrCoMnW alloys.