The microstructure and phase composition of an AlCoCrFeNi high-entropy alloy (HEA) were studied in as-cast (AlCoCrFeNi-AC, AC represents as-cast) and homogenized (AlCoCrFeNi-HP, HP signifies hot iso-static pressed and homogenized) conditions. The AlCoCrFeNi-AC ally has a dendritric structure in the consisting primarily of a nano-lamellar mixture of A2 (disordered body-centered-cubic (BCC)) and B2 (ordered BCC) phases, formed by an eutectic reaction. The homogenization heat treatment, consisting of hot isostatic pressed for 1 h at 1100 degrees C, 207 MPa and annealing at 1150 degrees C for 50 h, resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma (sigma) phase. Tensile properties in as-cast and homogenized conditions are reported at 700 degrees C. The ultimate tensile strength was virtually unaffected by heat treatment, and was 396 +/- 4 MPa at 700 degrees C. However, homogenization produced a noticeable increase in ductility. The AlCoCrFeNi-AC alloy showed a tensile elongation of only 1.0%, while after the heat-treatment, the elongation of AlCoCrFeNi-HP was 11.7%. Thermodynamic modeling of nonequilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents in the AlCoCrFeNi-AC and AlCoCrFeNi-HP. The reasons for the improvement of ductility after the heat treatment and the crack initiation subjected to tensile loading were discussed. Published by Elsevier B.V.

Due to their excellent properties and great potential for industrial application, eutectic high-entropy alloys (EHEAs) have been a hot topic of study over the past few years. The current study reports a novel AlCr1.3TiNi2 EHEA with a low density and outstanding mechanical properties at elevated temperatures. A kilogram-scale EHEA ingot with uniform and ultrafine L2(1) and BCC lamellar structures (interlamellar spacing similar to 400 nm) was firstly prepared by a direct solidification method. The as-cast AlCr1.3TiNi2 EHEA exhibits much higher room- and high-temperature hardness and specific yield strength values than most reported refractory high-entropy alloys (RHEAS), EHEAs, and conventional Ni- and Ti-based alloys. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The present work verifies the existence of chemical short-range orders (CSROs) in high-entropy alloys (HEAs) using a cluster-plus-glue-atom model. Two HEAs with a composition of Al2M14 (M = Ni4Co4Fe3Cr3 or Ni1Co1Fe2Cr1) are designed, which is derived from the cluster model of [Al-M-12](M2Al1) in face-centered-cubic structure or [Al-M-14]Al-1 in body-centered-cubic structure. It is found that the calculated pair-distribution functions (PDFs) at short inter-atomic distances by these cluster models can describe the neutron PDFs better than the ones by the average crystal structures. It is due to the different CSROs characterized by cluster units that induce the structural transition of HEAs. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The present work reports a cuboidal B2-coherently-enhanced body-centered-cubic (BCC) alloy Al0.7CoCrFe2Ni with prominent tensile properties at both room (ultimate tensile strength sigma(b) = 1223 MPa and elongation to fracture delta = 7.9%) and high temperatures. This multi-principal-element alloy is developed out of a cluster formula [Al-M-14]Al-1 issued from the cluster-plus-glue-atom model of a BCC structure. Here, the [Al-M-14] cluster is centered by Al, surrounded by fourteen average atoms M = Co1/2Cr1/5Fe2/5Ni1/5, and glued with one Al atom. Its excellent mechanical properties are attributed to a superalloy-like microstructure, characterized by cuboidal B2 nanoprecipitates coherently embedded in the BCC matrix. (C) 2016 Elsevier Ltd. All rights reserved.

We explore the atomic origins of the structural phase transformations (PTs) in AlxCrCoFeNi high entropy alloy (HEA) using classical molecular dynamics (MD) simulations. Our investigation critically reveals the role of Al content in triggering such diffusive transformations from a molten to a crystalline phase (for lower Al concentrations) or from molten to amorphous transitions (for Al fractions above the equiatomic alloy composition). Structural pair-correlation functions employed to provide atomistic evidence and mechanisms for the PTs show that the molten to amorphous PT initiates through the nucleation of a final child phase in the parent molten phase. Our structure predictions, although differ from earlier experimental observations, are confirmed by the predictions from common-neighbor analysis. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A new single-phase face-centered-cubic (FCC) Co9Cr7Cu36Mn25Ni23 [atomic percent, similar hereinafter] high-entropy alloy (HEA) was prepared by arc melting. A uniform distribution of nanometer-sized precipitates was achieved. The tensile yield strength, ultimate tensile strength, and elongation were 401 MPa, 700 MPa, and 36%, respectively. The energy-dispersive spectrometer results showed that the nano-precipitates were rich in Co and Cr elements. Moreover, the crystal-forming behavior and the nanoscale-precipitates-forming mechanism were revealed. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.