Refractory high-entropy alloys(RHEAs),composed of multiple refractory elements,such as Nb,Mo,Ta,W,Ti,Zr,Hf,in nearor non-equiatomic ratios,have recently emerged as promising structural materials for extreme environments due to their high melting points,excellent high-temperature mechanical properties,and superior micro structural stability.Compared to conventional HEAs based on elements like Ni,Fe,or Cr,RHEAs offer enhanced elevated-temperature performance but face challenges including segregation during solidification,relatively poor room-temperature ductility,and,most important,high-temperature oxidation.

To meet the increasing demand for continuously enhancing engineering performance and energy efficiency in a variety of aerospace and energy applications,structural materials with high strength at ultra-high temperatures are urgently required.In the past decade,refractory multi-principal element alloys(RMPEAs),particularly those containing elements with high melting temperatures(T_m)such as W and Ta(hereafter denoted as WTa-RMPEAs),have garnered extensive interest due to their exceptional strengths and thermally stability at high temperatures.Characterized by high T_m,sluggish diffusion,and severe lattice distortion,WTa-RMPEAs exhibit chemical composition fluctuations at different scales,leading to unique mechanical properties and deformation behavior.In this paper,an initial summary is provided of the mechanical properties of typical WTa-RMPEAs at room and high temperatures and the differences in deformation behavior and underlying mechanisms between RMPEAs and conventional alloys are discussed.Additionally,strengthening and toughening strategies and the suggested deformation mechanisms were reviewed.Finally,the challenges in revealing the actual deformation mechanism of WTa-RMPEAs were described,and a brief perspective on the future research of the mechanical behavior of WTa-RMPEAs was proposed.

Lithium-sulfur batteries(LSBs)have emerged as one of the most promising next-generation energy storage systems due to their high theoretical energy density(~2600 Wh·kg^-1)and cost-effectiveness.However,critical challenges,including polysulfide shuttling,lithium dendrite formation,and interfacial instability,persistently hinder their practical implementation.Conventional material design approaches face intrinsic limitations in reconciling structural stability with catalytic efficacy,underscoring the need for innovative solutions.High-entropy materials(HEMs),a novel class of multi-component systems typically comprising five or more principal elements,have recently demonstrated exceptional potential in addressing these challenges through their unique entropy stabilization effect,lattice distortion engineering,and multi-active site synergy.Since the advent of high-entropy alloys(HEAs),this design concept has been successfully extended to oxides,sulfides,nitrides,and electrolyte systems,where it exhibits unparalleled advantages in LSB applications.This review systematically evaluates recent advancements in the engineering of HEMs for sulfur cathodes,lithium metal anodes,and liquid electrolytes,with a focus on elucidating the mechanistic underpinnings of their enhanced ion transport,catalytic conversion,and interfacial stabilization capabilities.By establishing structure-property relationships and delineating performance optimization pathways,this work constructs a robust framework to accelerate the development of HEMs in energy storage systems while highlighting critical challenges and strategic directions for scalable deployment.

Maintaining thermal stability is a key concern for the potential application of multi-principal-element alloys(MPEAs)at elevated temperatures,particularly in the intermediate temperature range.In this regime,the thermodynamic dominance of the entropy term over enthalpy may diminish,while atomic migration remains kinetically active.In this study,the stability of a series of refractory MPEAs(RMPEAs)from the subsystems of Ti-V-Zr-Nb-Hf-Ta is investigated at 550℃for 2-28 days.Although all eleven alloys exhibit a single solid solution phase with a body-centered cubic structure at their homogenized states,only two alloys,VNbTa and TiVNbTa,remain stable after annealing.Decomposition occurs in the other nine alloys under the spinodal manner or the nucleation and growth mechanism,including all three quinary alloys,demonstrating that configurational entropy is not a dominant factor.The phase stabilities can be well understood from the enthalpy perspectives,by combining first-principles calculations and semi-empirical models.By comparing the different contributors of formation enthalpy,the lattice distortion energy is found to be the most critical factor for this alloy system.Furthermore,the phases formed after long-term annealing are generally located at different regions in the space with the axes of chemical,structural,and lattice distortion energies.This work provides a way to interpret and control the stability of RMPEAs in the intermediate temperature regime.

To develop ultra-strong high-density bulk materials with large deformability,we introduce a multiphase design strategy in a WMoVFeNi multicomponent alloy(MCA)system,and demonstrate it by investigating two prototype MCAs,i.e.,W₅₀Mo₁₀V₅(Fe₆₄Ni₃₆)₃₅and W₅₅Mo₁₅V₅(Fe₆₄Ni₃₆)₂₅(at.%).The two bulk MCAs were fabricated by mechanical alloying(MA)plus spark plasma sintering,and systematically analyzed in terms of elemental distribution,phase structure evolution,mechanical properties,and deformation mechanisms.The nanocrystalline powders are mainly composed of body-centered cubic(BCC)and face-centered cubic(FCC)phases after the MA process for 15 h.Upon sintering,the bulk MCAs show a multiphase structure consisting of a fine-grained BCC matrix,two different FCC phases,and a minor V-rich BCC phase.Particularly,the bulk W₅₀Mo₁₀V₅(Fe₆₄Ni₃₆)₃₅MCA sintered at 1250℃for 10 min exhibits an average mass density of 14.94 g·cm^-3,compressive yield strength of 1255 MPa,ultimate strength of 2639 MPa,and fracture strain of 32%at room temperature.Apart from the massive substitutional solid solution strengthening,the multiphase structure contributes significantly to the enhanced strength and deformability.The work thus provides a promising approach for the development of strong and tough high-density materials.

Martensitic transformation offers a pathway to overcome the room-temperature brittleness of refractory high-entropy alloys(RHEAs).The resulting extensive formation of the hexagonal close-packed(hcp)α-martensite necessitates deformation coordination via twinning to sustain plasticity during mechanical loading.However,the synergistic formation of multiple twin types and their effect on work hardening remain unclear.Employing advanced characterization techniques,this study identifies three primary martensitic twin systems({1011},{1012},and{1341}),two secondary twin configurations({1011}-{1341}and{1341}-{1011}),and three{1341}twin variants in metastable Ti₂₇Zr₄₀Hf₂₃Ta₁₀RHEAs.The presence of multiple martensitic twins generates dense twin interfaces that refine the grain structure while effectively hindering dislocation motion,thereby enhancing strain hardening capacity.The coexistence of multiple martensitic twins increases the number of independent slip systems within grains and induces variations in slip systems across different regions of the grains.This heterogeneity in slip systems accommodates multi-directional plastic deformation,consequently improving the material's sustained hardening capability.These findings underscore the critical role of synergistic twinning mechanisms in governing the work hardening of metastable martensitic RHEAs.

The urgent need to overcome the strength-ductility trade-off of nickel-aluminum bronze(NAB)in deep-sea engineering motivates the design of a Cu-bearing multi-principal element alloy(MPEA),Cu₃₅Ni₃₅Co₃₀,via magnetic levitation melting.The as-cast Cu₃₅Ni₃₅Co₃₀ MPEA exhibits a dual face-centered cubic(FCC)structure with superior mechanical properties(yield strength:~503 MPa,ultimate tensile strength:~686 MPa,total elongation:~11.0%)over its counterparts fabricated by vacuum arc melting.A single-phase FCC structure was obtained by homogenizing at 1030℃ for 15 h.Cold rolling and postdeformation annealing(PDA)were used to construct heterogeneous grain structures,which were achieved in PDA-treated samples at 1030℃ for 45 s(PDA-1030-45s)and 60 s(PDA-1030-60s).The PDA-1030-45s sample,composed of nano-sized recrystallized grains and residual deformed grains(RDGs),showed the best strength among the PDA-treated samples(a yield strength of~864 MPa,an ultimate tensile strength of~959 MPa,and a total elongation of~13.4%).The PDA-1030-60s sample with micro-sized recrystallized grains and RDGs exhibits an excellent combination of strength and ductility,showing a yield strength of~560 MPa,an ultimate tensile strength of~761 MPa,and a total elongation of~32.9%.These mechanical strengths are superior to those reported by NAB.The dominant strengthening mechanisms of the PDA-1030-45s and the PDA-1030-60s samples are dislocation strengthening and hetero-deformation-induced strengthening,respectively.

In this work,excess Cr₂O₃powders(by adding 25%,50%,and 75%Cr atoms relative to an equiatomic composition,respectively)are added to obtain equiatomic high entropy carbide ceramics with a single-phase rock salt structure via the technology of carbothermal reduction and spark plasma sintering.The effects of excess Cr₂O₃addition on the solid solubility of Cr,elemental distribution,and mechanical properties of(Ta₁Ti₁V₁Cr_x)C₄ceramics are investigated in detail.With the increase of excess Cr₂O₃addition,the Cr atom ratio of the synthesized powders increases from 7.0 at.%to 14.5 at.%,where Cr partially participates in the solid solution reaction to form(V,Cr)C solid solutions,while the remainder continues to exist in the form of Cr₂O₃powders.During spark plasma sintering,(V,Cr)C solid solutions dissolve into the(Ta,Ti)C solid solutions,resulting in a single-phase structured ceramics with dense and uniform element distribution.When the addition of excess Cr₂O₃is 25% and 50%,Cr atoms reach the equiatomic ratio in the as-sintered specimens.And the increase in Cr solid solubility is mainly attributed to the residual Cr₂O₃powders reacting with free carbon to form Cr₃C₂,which then dissolves into(TaTiVCr)C ceramics during high-temperature sintering.Additionally,with the increase of Cr solid solubility,the nano-hardness of(TaTiVCr)C ceramics is improved,reaching up to 34.75 GPa with 50%excess Cr₂O₃addition,owing to the lattice distortion and solid solution strengthening caused by the relatively small atomic radius of Cr.

Oxygen-induced microstructural evolution critically governs the long-term reliability of refractory multi-principal element alloys(RMPEAs)in extreme environments,where oxygen ingress during prolonged high-temperature service can drastically alter micro structural stability and mechanical performance,yet its atomic-scale mechanisms remain poorly understood.Here,oxygen's dual role in NbZrTi-based RMPEAs is systematically revealed through aging experiments at 650℃for 48and 168 h,combined with multiscale characterization.High-oxygen alloys(3 at.%O)exhibited multi-phase precipitation,including Zr-O-enriched hexagonal close-packed and dual body-centered cubic phases(Zr+Ti-O-rich and Nb+Ti-rich),governed by oxygen redistribution and thermodynamic stabilization.Contrary to conventional precipitation hardening,oxygen segregation gradients at the grain boundaries induced lattice distortion mitigation in the matrix,leading to a twostage age-softening behavior:rapid initial hardness reduction(20%within 48 h)followed by a plateau regime.The interplay between oxygen-mediated phase separation and concentration-dependent solute partitioning highlights the delicate balance required to optimize RMPEAs for high-temperature applications.These findings establish oxygen concentration thresholds and grain boundary engineering as critical design parameters for RMPEAs,enabling simultaneous optimization of radiation resistance and century-scale stability in next-generation nuclear reactor structure materials.

To improve strength and ductility of Ti-Zr-Nb lightweight refractory multi-principal element alloys(LRMPEAs)simultaneously,which is difficult for traditional solution strengthening and second-phase/precipitate strengthening,the compositional inhomogeneity in TiZrNb ternary equimolar LRMPEAs with a single-phased body-centered cubic structure is stimulated and tailored by doping V element.When V is introduced,compositional inhomogeneity shows as the segregation of V and Zr elements form.As the value of x for TiZrNbV_xLRMPEAs increases from 0.3 to 0.6,the mild compositional fluctuation develops to the spinodal decomposition structured three-dimensional framework with a periodicity of~5 nm.Then the dislocations in TiZrNbV_0.6LRMPEA are compactly pinned,a remarkable strengthening effect(~120 MPa)while the Frank-Read sources for dislocation multiplication and cross-slip are stimulated.Thus,an optimal combination of strength and ductility including the yield strength of 883 MPa and the fracture elongation of 26.6%is achieved in TiZrNbV0.6 LRMPEA.This work provides a useful method to enhance the strength of Ti-Zr-Nb LRMPEAs without sacrificing the ductility.This way is expected to be effective for other multi-principal element alloys,including high-entropy alloys and medium-entropy alloys.