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It remains challenging to develop low-cost body-centered cubic (BCC) high-entropy alloys (HEAs) with superior mechanical properties. In this work, we investigated the microstructure and mechanical properties of BCC FexCrNiAl0.5Ti0.5 HEAs containing L21 nanocrystals. With increasing the Fe content from Fe2 to Fe4 and Fe6, the formation of a big blocky L21 phase and a σ phase can be fully suppressed, and the size and fraction of the L21 crystals also decrease. Fe4 and Fe6 HEAs exhibit an optimized dual-phase microstructure with high-density L21 nanocrystals homogeneously distributed in the BCC matrix. Fe4 and Fe6 HEAs show high strength and do not fracture even at a large compressive strain of 70%, exhibiting the best combination of strength and fracture strain among all the reported BCC HEAs with nanocrystals. The superior mechanical properties of Fe4 and Fe6 HEAs are attributed to the optimized microstructure. These findings promote the development of low-cost HEAs with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Investigating the strength–plasticity synergy of metal structural materials is a crucial scientific challenge. This study focuses on preparing high-entropy alloys (HEAs) comprising Fe–Ni–Cr–Al, which exhibit a heterostructural coexistence of several phases through cold rolling and aging (CRA). Above 600 °C CRA, the average grain size of the HEA was refined from 260 to 1.64 μm, and numerous annealing twins were formed. Concurrently, two forms of irregularly ordered body-centred cubic (B2) phases and nanoscale ordered face-centred cubic (L1 2) phases were precipitated. Large B2 particles precipitated along the grain boundary, whereas small B2 and L1 2 particles precipitated within the grains. The average sizes of the B2 and L1 2 particles were 510 and 2.21 nm, respectively. The fine grain and precipitation strengthening enhanced the HEA yield strength (from 254 to 710 MPa). The difference in plastic strain between the matrix and precipitate causes long-range back-stress strengthening and heterodeformation-induced hardening, enhancing the strain-hardening ability and maintaining the superior plasticity of the HEA. This study provides an effective approach for obtaining metal structural materials with strength–plasticity synergy. • A FCC/L1 2 /B2 phases co-existed heterostructure HEA was designed. • The aging temperature changed the precipitation type of the second phase. • The mothod of deformation and thermal treatment obtained HEA of matching strength and plasticity. [ABSTRACT FROM AUTHOR]

Abstract Alloy powders with dual-phase nanocrystal (NC) and nanoglass (NG) have received much attention due to its small coercive force and high permeability, but the preparation of dual-phase high entropy alloy powders (HEAPs) simultaneously with larger aspect ratio constitute a great difficulty in microwave absorbing domain. Here, a new concept has been devised to tune the crystallinity of microwave absorber by regulating the phase proportion of milling precursor. A combination technology containing melting, strip casting, and milling has been adopted to prepare a serious of FeCoNiSi x Al 0.4 HEAPs to verify its correctness. Selective phase transition occurs in dry-milling process, generating various unique microstructures - NCs, NGs, and NGs embedding in NC grain. Besides, BCC phase content of HEAPs can be controlled by the amount of added ethanol. A less coercive force, increasing from 14.05 Oe (C 0.1) to 23.43 Oe (C 0.5), and a large magnetic permeability, varying from 2.41 (C 0.5) to 2.80 (C 0.3) at 1 GHz, can be obtained. Highlights • The crystallinity of powders relate to FCC phase proportion of milling precursor. • The phase structure of nanocrystal alloy ribbons can be tuned by element content. • Co-existed phase transitions promote the formation of dual-phase microstructure. • The variety of crystallinity lead to the change of magnetic properties. [ABSTRACT FROM AUTHOR]

The stability of body-centered cubic (β) phases and phase transformations of Nb x HfZrTi ( x  = 1, 0.6, 0.4 and 0.2) high-entropy alloys (HEAs) were investigated. Three types of transformations were observed: the β → ω transformation during cooling in Nb0.2 HEA, the deformation-induced β → α″ and β → α′ transformations in Nb0.4 and Nb0.2 HEAs, respectively. This implies that the phonon anomalies, T 1 1/2(110) and L 2/3(111), as the origins of phase transformations in simple Ti, Zr and Hf alloys, also exist in composition-complex TiZrHf-based HEAs. However, the very small fraction of deformation-induced α′/α″ martensite in fractured Nb0.4 and Nb0.2 suggests a sluggish effect of transformation as compared with simple β-Ti alloys. [ABSTRACT FROM AUTHOR]

The effect of Ti content on the microstructure and mechanical properties regulation for Fe 45 Ni 30−x Cr 15 Al 10 Ti x high entropy alloys (HEAs) with a duplex FCC/BCC structure is investigated. The as-cast Fe 45 Ni 30−x Cr 15 Al 10 Ti x HEAs have typical dendrite and inter-dendrite structure, where dendric and inter-dendric regions are FCC and BCC phases, respectively. After introducing Ti, the inter-dendric structure transforms into coexistence of disordered BCC and ordered B2/L2 1 phases. And the morphology of B2/L2 1 precipitates gradually changes from a regular maze-like mesh and cuboidal structure to elliptical structures due to the increase of the lattice mismatch. The change of precipitate type and volume fraction lead to that the ultimate tensile strength of the HEAs increases from 540 MPa to 1292 MPa. Meanwhile, it keeps the uniform elongation of 13.29%, showing outstanding strength-plasticity synergy. • A multi-phase coexistence HEA with superior mechanical property was designed. • The addition of Ti led to precipitation of hierarchical B2/L2 1 phase from BCC phase. • As the Ti content increased, the morphology of precipitates changed. [ABSTRACT FROM AUTHOR]

A Ti 3 Zr 1.5 NbVAl 0.25 refractory high entropy alloy (RHEA) was prepared by vacuum melting and subsequently subjected to hot forging and annealing at elevated temperatures. The as-prepared alloy has a single body-centered cubic (BCC) phase structure with a balanced matching of strength and toughness. It is shown that tensile yield strength and fracture elongation of this alloy are 899 MPa and 24.50%, respectively. In addition, the Charpy V-notch impact toughness of the Ti 3 Zr 1.5 NbVAl 0.25 alloy was measured to be 119. 5 J/cm2, which is better than most traditional alloys and HEAs. The superior quasi-static and dynamic mechanical properties synergy makes this RHEA attractive for advanced structural applications. [ABSTRACT FROM AUTHOR]

A new method was proposed to pinpoint the compositions with good glass forming ability (GFA) by combining atomic clusters and mixing entropy. The clusters were confirmed by analyzing competing crystalline phases. The method was applied to the Zr–Al–Ni–Cu–Ag alloy system. A series of glass formers with diameter up to 20 mm were quickly detected in this system. The good glass formers were located only after trying 5 compositions around the calculated composition. The method was also effective in other multi-component systems. This method might provide a new way to understand glass formation and to quickly pinpoint compositions with high GFA. [ABSTRACT FROM AUTHOR]

The Boltzmann formula was commonly employed to describe the configurational entropy of high entropy alloys (HEAs) based on the assumption of ideal solid solution, however, the entropy might rather be called composition entropy cautiously due to the site preference on the sublattice was omitted. Here we proposed a reasonable and general approach beyond the Boltzmann formula to describe the site occupying fractions (SOFs) of atoms on sublattices and thus the configurational entropy of HEAs. For this purpose, the thermodynamic function of the chemical reaction of complex HEA involving SOFs synthesized from the corresponding pure elements was computed using the sublattice model, where the density functional perturbation theory (DFPT) was employed to calculate the relevant thermodynamic properties at definite temperature. Three typical high entropy alloys with different phase structures were quantatively calculated and graphically demonstrated. The site preferences exist due to the different atom characters and sublattice environments. For example, Ni atoms only occupy the 1a sublattice, while Co, Cr, and Fe atoms mainly occupy the 3c sublattice in FCC_CoCrFeNi HEA, and the site preferences tend to be weakened considerably with the increase of heat treatment temperature. The configurational entropies were thus re-defined based on the sublattice information and SOFs. The calculated configurational entropies for FCC_CoCrFeNi HEA are 7.95, 9.10, and 9.49 J/mol·K at 473K, 973K, and 1473K, respectively, while those for BCC_AlCoCrFeNi are 11.68, 13.18, and 13.34 J/mol·K, respectively, and for HCP_HfScTiZr HEA are 11.22, 11.39, and 11.46 J/mol·K, respectively, all the configurational entropies are less than the calculated values using Boltzmann formula based on the composition. From the atom distributing configuration based on SOFs, the short range or the local ordering behaviors were explored further by statistically analyzing the coordination number among the same type of atoms, and we found that the coordination number is far less than the coordination number of the corresponding pure metal with FCC, BCC or HCP structure, and the size of the cluster formed from the same type of atoms is considerably small. The quantative and graphical characterizations of HEAs are essential to give a clue for the high resolution experiment at the atomic level, as well as provide the indispensable structural information used to predict the lattice distortion and diverse properties further. Fig. Visualization of atomic distribution with the real relative size on the sublattice 1a and 3c, as well as on the full FCC lattice for FCC_CoCrFeNi HEA subjected to heat treatment to equilibrium at 973K. The site preference of atoms is considerably strong. For the CoCrFeNi high entropy alloy with FCC phase structure, Ni atoms strongly favor 1a sublattice, and the Co, Cr, and Fe atoms prefer to 3c sublattice when the phase reaches its equilibrium at 973K. The local ordered cluster is identified directly. [Display omitted] • We proposed a reasonable approach based on site preference to describe atom distribution and configurational entropy of HEAs. • The model is beyond the previous Boltzmann formula based on composition to suppose atoms occupy randomly on the lattice. • The fine lattice structures of the demonstrated HEAs were quantitatively and graphically characterized. • The reasonable description of the atom distribution is crucial to predict the lattice distortion and properties further. [ABSTRACT FROM AUTHOR]

We studied the thermodynamics and kinetics of a non-equiatomic Ti 32.8 Zr 30.2 Ni 5.3 Cu 9 Be 22.7 high entropy metallic glass (HEMG, ΔS config. ∼1.44R) with a critical size for glass formation over 50 mm. The characteristic transition temperature, enthalpy of transition and specific heat capacity along with the relaxation time at different heating rate were determined using differential scanning calorimeter (DSC) measurements. It reveals that the present HEMG supercooled liquid shows the lowest thermodynamic driving force against the nucleation and growth of crystalline phases with comparing to other typical MG formers. Meanwhile, it exhibits the ultrastrong behavior near glass transition in terms of the Angell's fragility concept. The alloy has a fragility index of D* = 45.2, higher than all the typical MG formers reported so far. Both thermodynamic and kinetic factors are responsible for the ultrahigh glass-forming ability of the HEMG alloys. [ABSTRACT FROM AUTHOR]

Refractory high entropy alloys (RHEAs) with good high-temperature softening resistance have been revealed as promising candidates for high-temperature structural materials. In this work, a low-density ductile RHEA, Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 , has been developed. The RHEA with a BCC matrix and B2 nanoprecipitates exhibits excellent specific yield strength. The compressive specific yield strength (σ 0.2 /ρ) at 1073 K is as high as 83.2 MPa g−1 cm3. The different deformation behaviors during compression at 1073 K and 1273 K are also identified. The dislocation-dominated deformation provides the initial strain hardening capability, and then microcracks and dynamic recovery accelerate the transition from strain hardening to softening at 1073 K. While the diffusion-controlled dislocation annihilation and continuous dynamic recrystallization (DRX) are the dominant reasons for persistent strain softening at 1273 K. Our work not only reports a promising RHEA with excellent high-temperature properties, but also promotes the development of RHEAs for high-temperature applications. • A low-density ductile RHEA, Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 , has been developed. • The RHEA has BCC matrix and B2 nanoprecipitates. • The RHEA possesses the superior SYS (σ 0.2 /ρ = 83.2 MPa g−1 cm3) at 1073 K. [ABSTRACT FROM AUTHOR]

• A novel high specific strength plastic Ti 1.5 ZrNbAl 0.3 RHEAs was developed. • The tensile specific yield strength of this alloy is up to 145.5 MPa g−1 cm3. • The tensile fracture elongation of this alloy is up to 23.0%. • The specific yield strength-plasticity synergy is the best among all other RHEAs. • Short-rang orderings and cross-slip generate the strength-plasticity synergy. The ambient temperature brittleness and high density of refractory high entropy alloys (RHEAs) are the obstacles for their applications as structural materials. A novel ductile body-centered cubic Ti 1.5 ZrNbAl 0.3 RHEA with high specific strength was developed. The tensile specific yield strength and fracture elongation of this alloy are 145.5 MPa · g−1 · cm3 and 23.0%, respectively. The specific yield strength is the highest among all other reported RHEAs. The superior mechanical properties of the Ti 1.5 ZrNbAl 0.3 RHEA arise from the solid solution strength and cross-slip of dislocations. The ultrahigh specific yield strength and superior strength-plasticity synergy may promote the applications of RHEAs. [ABSTRACT FROM AUTHOR]