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Coarsening is a metallurgical process that is related to solute transmission and system energy decrease. However, for the coarsening behavior of the L12 precipitate in high-entropy alloys, the influence of moving boundary is still an open question. Here, we found the moving boundary accelerates the discontinuous coarsening of L12 phase. The multiple defects-accelerated diffusion and continual particle-capturing ability of the moving boundary provide a high-efficiency solute transport for the fast-coarsening kinetics of L12 phase. In addition, a boundary-encountered assisted precipitate formation mechanism is also validated in the recrystallized area. [ABSTRACT FROM AUTHOR]

The eutectic high entropy alloys with large amounts of Al and Cr have exhibited superior oxidation resistance. Here, we confirmed that Si could further enhance the oxidation resistance by forming a continuous oxidation layer in Fe36Ni36Al15Cr10Si2Mo1 alloy. Si promoted the outward diffusion and transformation of Al which effectively enhanced the oxidation resistance. The FeCr2O4 spinel and silicate formed by the solid-state reaction also contributed to the oxidation resistance. The thermodynamic and kinetic factors were then discussed to understand the inherent oxidation mechanism of the dual-phase Fe36Ni36Al15Cr10Si2Mo1 alloy, which provide new insights into the dual-phase alloy design and oxidation resistance. [ABSTRACT FROM AUTHOR]

AlCrFeNi multi-component alloys with excellent mechanical properties have been designed and extensively investigated in recent years. The massive fabrication of sheets will be an effective way for industrial application, where hot rolling is the inevitable process. After hot rolling, the mechanical properties could be further tailored. In this study, the effects of heat treatments on a dual-phase Al17Cr10Fe36Ni36Mo1 hot-rolled plate were systematically investigated, including: (i) annealing (700 °C, 850 °C, 1000 °C and 1150 °C for 1 h, respectively), (ii) solution and single aging (1150 °C for 1 h and 700 °C for 4 h), (iii) solution and double aging (1150 °C for 1 h, 700 °C for 4 h and 650 °C for 1 h). The B2 precipitates with varied morphologies were observed in the FCC matrix of the hot-rolled alloy after a heat treatment range from 700 °C to 1000 °C for 1 h, and the BCC particles in the B2 matrix were dissolved when the heat treatment temperature was higher than 1000 °C. The hot-rolled alloy heat treated at 700 °C for 1 h had the highest yield strength, and the hot-rolled alloy treated at 1150 °C for 1 h showed the lowest yield strength. After a solution at 1150 °C for 1 h, aging at 700 °C for 4 h and 650 °C for 1 h, the L12 phase and BCC particles were precipitated in the FCC and B2 matrices, and B2 nanoprecipitates were observed around the FCC grain boundaries. The solution and double aging alloy exhibit the tensile strength of 1365.7 ± 9.5 MPa, a fracture elongation of 14.2 ± 1.5% at 20 °C, a tensile strength of 641.4 ± 6.0 MPa, and a fracture elongation of 16.9 ± 1.0% at 700 °C, showing great potential for application. [ABSTRACT FROM AUTHOR]

The metastable-stable transition and rapid coarsening of metastable D022 phase remains its Achilles hell, restricting the application of D022-strengthened alloys at service temperatures higher than 650°C. Hence, it is crucial to improve thermal stability of D022 phase. In this work, we report an 800°C-stable D022-Ni3(W0.24Ti0.38Ta0.19Nb0.19) superlattice in the Ni58Cr23Fe10W5Ti2Ta1Nb1 MEA. Experimental results and theoretical analysis showed that the exceptional thermal stability is due to Nb-sublattice occupying elements, low diffusivity of W, and extremely small lattice misfit between the D022 phase and FCC matrix. These findings shed lights on developing high-performance D022-hardened alloys capable of operating at temperatures above 650°C. [ABSTRACT FROM AUTHOR]

Dual-phase high-entropy alloys with excellent room temperature and high-temperature properties have been widely studied as potential high-temperature structural materials. However, interface weakening causes its high-temperature performance to decline at higher temperatures, severely limiting further development. In this study, a series of Al17Cr10Fe36Ni36Mo1Hfx (x = 0, 0.03, 0.15, 0.3, 0.5, and 0.8 at%) alloys were prepared to study the effect of Hf content on the microstructure and mechanical properties of the matrix alloy. The results indicate that with the addition of the Hf, the Hf-rich phase began to precipitate at the interface and inside the B2 phase in the matrix alloy. In contrast, the morphology of both the FCC and B2 phases had no noticeable change. With the increase in Hf content, the high-temperature strength and ductility of the alloy first increased and then decreased, while the room temperature performance remained almost unchanged. Benefiting from the hindrance of the Hf-rich phase to grain boundary sliding and dislocation movement during high-temperature deformation, the tensile strength, yield strength, and plasticity of the matrix alloy increased from 474 MPa, 535 MPa, and 8.7% to 816 MPa, 923 MPa, and 42.0% for the Al17Cr10Fe36Ni36Mo1Hf0.5 alloys, respectively. This work provides a new path for designing a high-entropy alloy with excellent high-temperature mechanical properties. [ABSTRACT FROM AUTHOR]

Eutectic high-entropy alloys (EHEAs) have excellent properties with in situ two-phase composites. In EHEAs, the combination of hard and soft phases generates promising applications in the area of wear. Laser remelting modification and heat treatment can be used to further regulate the surface microstructure for the enhancement of surface properties. In this investigation, the surface hardness of Ni32-xCo30Cr10Fe10Al18Tix EHEAs was significantly improved by laser remelting and subsequent aging. It was found that the remelted area of the alloy showed a refined microstructure and the nanoindentation confirmed the increased microhardness from the substrate to the remelted area. The optimal aging process was explored to further strengthen the surface by introducing precipitates while avoiding severe coarsening of the matrix. The surface of the remelted and the aged Ni29Co30Cr10Fe10Al18Ti3 alloy has the highest average microhardness of ~ 620 HV. [ABSTRACT FROM AUTHOR]

Excellent ductility is crucial not only for shaping but also for strengthening metals and alloys. The ever most widely used eutectic alloys are suffering from the limited ductility and losing competitiveness among advanced structural materials. Here we report a distinctive concept of phase-selective recrystallization to overcome this challenge for eutectic alloys by triggering the strain hardening capacity of the duplex phases completely. We manipulate the strain partitioning behavior of the two phases in a eutectic high-entropy alloy (EHEA) to obtain the phase-selectively recrystallized microstructure with a fully recrystallized soft phase embedded in the skeleton of a hard phase. The resulting microstructure fully releases the strain hardening capacity in EHEA by eliminating the weak boundaries. Our phase-selectively recrystallized EHEA achieves a high ductility of ∼35% uniform elongation with true stress of ∼2 GPa. This concept is universal for various duplex alloys with soft and hard phases and opens new frontiers for traditional eutectic alloys as high-strength metallic materials. The ever most widely used eutectic alloys often suffer from limited ductility. Here the authors propose a distinctive concept of phase-selective recrystallization to significantly improve their ductility and strength and pave the way for new applications of the widespread eutectic alloys. [ABSTRACT FROM AUTHOR]

Recrystallization has been a major method to induce heterogeneous grain structure for improving the strength–ductility combination of single-phase high-entropy alloys (HEAs). However, the recrystallization kinetics, which are the guideline for controlling the recrystallization behavior, of single-phase HEAs are relatively less explored. Here, we uncover the recrystallization behaviors of typical single-phase NiCoCrFe and Ni2CoCrFe HEAs. Our results showed that the two investigated HEAs exhibit almost similar recrystallization activation energy around 230 kJ·mol−1, but distinctively different recrystallization kinetics. This abnormal difference is attributed to the deformation twins of NiCoCrFe. These findings indicate that, except for textbook factors, deformation twinning significantly enhances the recrystallization behavior of HEAs. [ABSTRACT FROM AUTHOR]

• A machine learning model for eutectic high entropy alloys in Al–Co–Cr–Fe–Ni system are established. • The eutectics formation in the high entropy system is uncovered via data mining with machine learning. • A novel eutectic high entropy alloy design method with three steps is proposed. Eutectics in high entropy alloys (HEAs) have shown excellent properties and promising applications. With empirical rules, various of eutectic high entropy alloys (EHEAs) have been proposed. The current design strategies shed light on the formation of eutectics in HEAs, but they are incapable of confirming multiple variables quantitatively in the selection of a specific system. In the present study, the eutectic formation in the multi-principal element systems is uncovered via data mining with machine learning (ML), where the critical elements and strongly associated elements were discovered. Taking the Al–Co–Cr–Fe–Ni system as an example, Al is confirmed to be the critical element for the eutectic formation and Cr is the strongly associated element with Al, Ni, Co, Fe and minor additions with comparably large solid solubility can be considered overall. With these understandings, a three-step approach can be summarized for designing EHEAs in a given system. Within the designed EHEAs, properties can be tested for optimization of application orientated design. The findings can not only accelerate the exploitation of EHEAs with better performance but also provide new ideas for designing compositionally complex alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The eutectic high-entropy alloys have shown promising mechanical behaviors while their softening at elevated temperatures is still a challenge. Generally, the boundaries are the weak parts to be strengthened with increased temperatures in eutectic high-entropy alloys. Here, we found that the minor addition of boron in Ni 30 Co 30 Cr 10 Fe 10 Al 18 W 2 eutectic high-entropy alloy can significantly strengthen the FCC grain boundaries and the FCC/B2 phase boundaries at elevated temperatures. A remarkable tensile yield strength over 581 MPa with elongation of 71 % at 800 °C is achieved with minor boron addition, corresponding to a 45 % increase in yield strength and 129 % improvement in ductility compared with the boron-free counterpart. Accompanied by the boron-strengthened phase boundary, sustainable dynamic recovery occurs in the FCC and B2 phases during high-temperature tensile testing, ensuring excellent ductility. Moreover, the benchmark test indicates that the strengthening effect of boron and borides on the boundaries contributes up to 166 MPa to the yield strength of eutectic high-entropy alloy at 800 °C. These findings shed light on the development of high-temperature eutectic high-entropy alloys with a microalloying strategy. [Display omitted] [ABSTRACT FROM AUTHOR]

• Phase-selective recrystallization and aging was applied to the FeNiCrAl alloy. • Effect of aging on the microstructure and mechanical properties were studied. • The tensile elongation significantly increases via phase-selective recrystallization. • The aged alloy shows ultimate strength of 1369.0 MPa and elongation of 23.0%. Phase-selective recrystallization process has been confirmed as an effective way to improve the ductility of dual-phase alloys. Here, the tensile property of a low-cost dual-phase Fe 37 Ni 36 Cr 10 Al 17 alloy was significantly improved via phase-selective recrystallization and aging. The equiaxed microstructure was obtained after phase-selective recrystallization and the tensile elongation significantly increases compared with as-cast alloy. Furthermore, the tensile strength increased to 1369.0 MPa and elongation increased to 23.0% by aging. The comprehensive property shows great potential applications for industrial prospects. [ABSTRACT FROM AUTHOR]

• A casting eutectic high entropy alloy Ni 30 Co 30 Cr 10 Fe 10 Al 18 W 2 was designed and prepared. • The alloy consists of soft FCC and hard B2 eutectic phases with the semi-coherent interface. • The alloy possesses a tensile strength of 1266.5 MPa and an elongation of 20.3% in the as-cast condition. Mechanical properties of casting alloys are generally limited. To make casting alloys applicable for a high level of service environments, a novel casting eutectic high entropy alloy (EHEA) with excellent mechanical properties is proposed. The hierarchical microstructures are with fine regular lamellar eutectic and coarse irregular eutectic. The eutectics consist of face-centered cubic (FCC) and ordered body-centered cubic (B2) phases with the semi-coherent interface. In the as-cast state, it shows a tensile strength of 1266.5 MPa and elongation of 20.3%. The unusual as-cast properties make it possible to manufacture high performance products by direct casting. [ABSTRACT FROM AUTHOR]

Atomic packing problems have been widely investigated by physicists, mathematicians, material scientists as a long-standing scientific issue. While it is widely known that the monodisperse particles are closely packed into the face-centered cubic structure, the increase of polydispersity will suppress the crystallization. It is still unsolved when and how the crystalline packing collapses as the particle-size difference increases over a critical value. On the other hand, the atomic-size factor of the solution has gone deeply into the concept of applied physicists and physical metallurgy scientists since the proposal of Hume-Rothery rules in 1934. Although great efforts have been devoted to understanding this simple but important empirical rule of the atomic size effect, it remains a question without a complete answer even in binary alloy systems. Here, the two outstanding issues were solved in a rigorous geometric packing instability model even in the multicomponent system. The physical scenario presented here are helpful for understanding the close packing instability and the atomic-size effect in the Hume-Rothery rules. • A geometrical model of packing instability was proposed. • The 15% atomic size difference rule in solid solution was proved. • The instability criterion of size effects in multicomponent case was presented. • The analyses is applicable to metallic alloys, granular materials and colloidal system. [ABSTRACT FROM AUTHOR]

Abstract The variation of the lattice constant with alloying elements is an essential issue in alloy design. In the traditional single-based alloys, there is a tremendous database for predicting the lattice constant. However, the traditional database is not suitable to the emerging multi-principal components alloys referred as high entropy alloys. Here, a framework is proposed to describe the variation of lattice constants in high entropy alloys. Based on the quantitative measurement of the lattice constants of fourteen alloys, we constructed the lattice constant database for concentrated CoCrFeNi alloys. The discrepancy between binary alloys and high entropy alloys revealed the atomic chemical interactions. Graphical abstract Quantitative determination of the lattice constant in CoCrFeNi high entropy alloys. A model is proposed to describe the lattice constant in high entropy alloys. The coefficients in the model are obtained from the precise XRD measurements of designed CoCrFeNi alloys with different compositions. The results greatly derivate the traditional binary alloys. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Eutectic high entropy alloys (EHEAs) have shown promising mechanical properties and good castability. However, designing EHEAs is still a challenge because of highly complex chemical compositions and limited multiple phase diagrams. Here, we propose a grouping strategy to design EHEAs efficiently based on the distributions of mixing enthalpies of atom-pairs in multi-principal-component alloys. Following this idea, a new CoCrFeNiTa 0.43 EHEA is designed successfully. Moreover, those reported EHEAs are reviewed and show high consistence with the strategy proposed here. Highlights • A new strategy for the design of eutectic high entropy alloys is proposed. • The EHEAs can be designed by mixing a solid solution group and an intermetallic group. • The CoCrFeNiTa 0.43 HEA with eutectic structure is successfully designed following this group strategy. [ABSTRACT FROM AUTHOR]

Abstract The face centered cubic (FCC) high entropy alloys (HEAs) showed highly attractive properties because of their simple crystal structures and low stacking fault energies. However, deep understandings of micro-alloying in FCC HEAs, including solid solubility, precipitates formation and stacking fault energy variation, remain unsatisfactory. In present study, we systematically investigated the solubility of Ti, Al, and Mo in the CoCrFeNi HEA and evaluated the effect of every single element on the precipitation behavior. The results showed that at 750 °C the CoCrFeNi matrix can separately dissolve up to 0.6 at.% Ti, 4 at.% Al, and 3 at.% Mo. The roles of both additional and base elements in the precipitation behaviors were identified. Specifically, Co can stabilize the γ′ phase in the Ti-doped HEAs, while Al leads to the formation of B2 phase in the CoCrFeNiAl x system. The annealing stacking faults and twins in the matrix changed with the addition of different elements, which was mainly due to stacking fault energy variations. These insights will greatly benefit the design of precipitate-hardening HEAs and provide a deeper understanding of metallurgical behaviors of HEAs. Highlights • The CoCrFeNi HEA dissolve 0.6 at.%, 4 at.% Al and 3 at.% Mo at 750 °C, respectively. • In the CoCrFeNi system, Co stabilizes the γ′ phase through decreasing the VEC. • The Al leads to the formation of B 2 phase at 750 °C, rather than the γ′ phase. • The Al and Ti decrease the stacking fault energy of CoCrFeNi while Mo increases it. [ABSTRACT FROM AUTHOR]

Extreme-low (even negative) and strong temperature-dependent stacking fault energy (SFE) is one of the most unique properties in face centered cubic (FCC) high entropy alloys (HEAs). Here, by making full use of this unique property, we present a proof-of-principle investigation of tuning defects in FCC HEAs through changing SFE during deformation. A qualitative model is proposed to predict the possibilities of different types of defects in FCC HEAs. Following this model, different defects combinations, instead of individual defects, are well controlled by rolling. FCC HEAs with balanced dislocation, stacking faults and twins show good balance between strength and ductility. [ABSTRACT FROM AUTHOR]

Though the strengthening effect of σ and μ phases in CoCrFeNiMox high entropy alloys has been confirmed, the selection of these two phases remains unclear, which restricts the further strengthening design. In this study, microstructures and phase compositions of CoCrFeNiMox (x = 0.1, 0.2, 0.3, 0.4, and 0.5) alloys were investigated through annealing at 600, 750, 900, 1000 °C for 7 days and 1080 °C for 3 days, respectively. Based on the experiment results, a (CoCrFeNi)-Mo phase selection diagram was drawn and compared with the calculated isopleth phase diagram of (CoCrFeNi)-Mo. The results indicate that the selection of σ and μ phases depends on the content of Mo greatly. Due to the limited prediction of phase selection and transformation by the isopleth phase diagram of (CoCrFeNi)-Mo, we design a (CoFeNi)-Mo-Cr isothermal phase diagram to reveal the transformation between σ and μ phases and their selections. [ABSTRACT FROM AUTHOR]

The W and Mo are in the same groups of periodic table and are usually used as solid solution elements. In this investigation, the minor alloying behaviors of W and Mo in Fe 37 Ni 36 Al 17 Cr 10 alloy were explored. The addition does not change the casting microstructure greatly, with dendrite region of FCC + B2 and inter-dendrite region of FCC phase. For tensile properties at ambient temperature, as-cast Fe 36 Ni 36 Al 17 Cr 10 Mo 1 alloy exhibited higher yield strength and fracture strength compared with Fe 37 Ni 36 Al 17 Cr 10 alloy. Then, dual-phase alloys with Mo content of 2 and 3 at% were further designed and carefully studied. It is found that a nano-scale structure occurred in as-cast Fe 35 Ni 36 Al 17 Cr 10 Mo 2 alloy, where a large number of spherical BCC precipitates are distributed in the dendrite region of B2 phase. Meanwhile a mixture of irregular B2 phase and FCC phase is contributed to the inter-dendrite area. The Fe 35 Ni 36 Al 17 Cr 10 Mo 2 alloy exhibited the most excellent and comprehensive mechanical properties due to the fine structure and its high work hardening ability. The yield strength, ultimate tensile strength and fracture elongation of as-cast Fe 35 Ni 36 Al 17 Cr 10 Mo 2 alloy are 863 ± 20 MPa, 1285 ± 17 MPa and 16.0 ± 1.0 %, respectively, which is higher than the most of reported dual-phase as-cast FeNiCrAl multi-component alloys. • The alloying behaviors of W and Mo in Fe 37 Ni 36 Al 17 Cr 10 alloy were explored. • Effect of Mo amount on the microstructure and mechanical properties were studied. • A nano-scale structure consisted of FCC, B2 and BCC occurred in as-cast alloy. • The Fe 35 Ni 36 Al 17 Cr 10 Mo 2 alloy exhibited the most excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Based on surveying the existing binary phase diagrams with eutectic points, a strategy of designing eutectic high entropy alloys (EHEAs) with desired high strength and ductility is proposed. Based on the computer-aided thermodynamic calculations, the pseudo eutectic binary alloy system of CoCrFeNiNb x (x = 0.1, 0.25, 0.5 and 0.8) was designed. The experimental results show that the eutectic alloys are composed of a ductile face centered cubic (FCC) phase and a hard Laves phase with fine laminar structures. The designed alloys show excellent integrated mechanical properties of ductility and strength. For the CoCrFeNiNb 0.5 alloy, the compressive fracture strength and strain can reach above 2300 MPa and 23.6%, respectively. [ABSTRACT FROM AUTHOR]

It is still a challenge to further increase the yield strength of eutectic high-entropy alloys, a promising multiple principal alloy system. By modifying the Ni: Co ratio to introduce the γ′ phase, we developed a series of Ni 60-x Co x Cr 10 Fe 10 Al 18 Mo 2 (x = 30, 20, 10, 0) casting hypoeutectic high-entropy alloys with improved yield strength and ductility. The increase of Ni concentration via decreasing Co concentration promotes the amount of FCC phase with nano γ′ particles in it. The as-cast Ni 60 Cr 10 Fe 10 Al 18 Mo 2 HEA with FCC/γ'+B2 phase composition exhibits a superior σ 0.2 –831 MPa due to the formation of the γ′ phase. The results provide a feasible route for developing high-performance Ni–Co–Cr–Fe–Al casting HEAs with multiscale microstructure. [ABSTRACT FROM AUTHOR]

Very recently, a method of phase-selective recrystallization has been proposed to significantly increase the ductility of eutectic alloys. Different from the conventional methods, such as adding modifiers and severe plastic deformation, phase-selective recrystallization is a simple way to control the microstructures with selective recrystallization of the soft phase but refining the hard phase. In this paper, we reveal the microstructure evolution in the phase-selective recrystallization treatment of Al–Si alloys. The results show that through phase-selective recrystallization, the microstructure of the eutectic Si phase with high degree of spheroidization and fine grains of the α-Al matrix can be obtained. Simultaneously, the refined hard Si particles and the soft α-Al grains brought the unusual tensile elongation of 24%, triple of that in as-cast state. Meanwhile, the ultimate tensile strength increased from 208 MPa to 291 MPa. The performance of Al–Si alloy with phase-selective recrystallization is superior to all previous treatments and can be used to produce high performance Al–Si alloy sheet with large scale. • High-performance A357 Al–Si alloy was simply prepared by cyclic rolling and recrystallization. • Cyclic rolling and recrystallization simultanously refined the eutectic Si and α-Al matrix. • The elongation and strength of A357 Al–Si alloy were simultanously enhanced. • Cyclic rolling and recrystallization showed great potentical in industrial application. [ABSTRACT FROM AUTHOR]

• Effects of pre-strain on precipitation kinetics and strengthening mechanisms of γ'-strengthened HEAs were studied. • Pre-strain can accelerate precipitation kinetics but shows a non-monotonous feature with the increase of pre-strain. • The shortened defects existing time by recrystallization can weaken the acceleration effect at high pre-strain. • Strengthening mechanisms can be tuned by different pre-strain to realize targeted properties. Pre-strain is often used as a powerful pre-treatment to tailor the microstructures and mechanical properties of traditional alloys. However, in high-entropy alloys (HEAs), the effect of pre-strain degree on the precipitates is still unclear. In this paper, we investigated the effects of pre-strain degree on the precipitation of Ni 2 CoCrFeTi 0.18 Al 0.12 high-entropy alloys. The HEAs were cold-rolled with different thickness reduction of 30%, 50%, and 70% and annealed at 800 °C for 30 ~ 60 min, followed by high-resolution scanning electron microscope (SEM) analysis. Counter-intuitively, we discovered a non-monotonous effect of pre-strain on the precipitation behavior, that low pre-strain can accelerate the precipitation behavior while such accelerating effect is weakened under high pre-strain. This non-monotonous effect is attributed to the shortened defects existing time by recrystallization under high pre-strain. In addition, pre-strain can controllably tailor the precipitation strengthening, dislocation strengthening, and grain boundary strengthening of HEAs. These results not only uncover the mechanism of the non-monotonous pre-strain effect on the precipitates but also provides a pre-strain mediated scheme for tuning the precipitation-strengthened HEAs to targeted properties. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have been investigated considerably in the last decade. The phase selection in HEAs has attracted much attention recently, especially on forming of the solid solutions. Up to now, phase diagrams of most HEAs are still not well developed, and the empirical phase selection rules play an important role in HEAs area. In this brief review, the physical factors controlling the phase stability in HEAs are discussed, and the phase selection rules are identified. Different from previous results, the rules on equilibrium phase selection within a certain temperature range are carefully reviewed and presented in this article. [ABSTRACT FROM AUTHOR]

High-/medium-entropy alloys (H/MEAs) with multiple principal elements and promising performance have opened up an unprecedented multi-dimensional compositional space for exploring novel materials. Here, we report a novel B2-strengthening Ni–Co–Cr–Al medium-entropy alloy system with a better combination of strength and ductility. Through simple thermomechanical processing, gigapascal yield strength (∼1 GPa) and ultimate strength (∼1.5 GPa) combined with excellent uniform elongation (∼22%) were achieved. This excellent strength-ductility synergy resulted from the partial recrystallization combined with considerable fine B2 precipitates, and annealing twins in this dual-phase Al13 MEA. This work further broadens material design and optimization space and offers a paradigm for developing heterogeneous microstructures in dual-phase MEAs through alloying and regulating recrystallization and precipitation behaviors. [ABSTRACT FROM AUTHOR]

The recently emerged CoCrNi-based medium-entropy alloys (MEAs)/high-entropy alloys (HEAs) have a good combination of high strength and ductility. However, there are still challenges for further increasing their mechanical properties by finding optimal composition with simple processing. In this investigation, we revisited the commercial superalloys MP35N and MP159 with similar composition and entropy to CoCrNi-based MEAs/HEAs to find inspirations for designing CoCrNi-based MEAs. After a simple thermomechanical process, MP35N/MP159 can achieve a high tensile strength over 2.2 GPa at ambient temperature, better than a majority of present CoCrNi-based MEAs/HEAs. At intermediate temperature tensile tests, the aged MP159 also has a considerable tensile strength (1.8 GPa) and tensile elongation (12.5%). The underlying strengthening factors of aged MP35N/MP159 were investigated by transmission electron microscope. It indicated that precipitation strengthening, solid solution strengthening, and work-hardening could be introduced in CoCrNi-based MEAs through alloying, and simple thermomechanical treatments to significantly improve the performance. The present findings and perspectives provide useful enlightenment for developing ultra-strong CoCrNi-based MEAs/HEAs. ● The compositions of MP35N and MP159 are similar to CoCrNi-based MEAs/HEAs, and the configurational entropy already falls in the range of MEAs/HEAs. ● At ambient temperature, both MP35N and MP159 have a tensile strength of 2.2 GPa, better than a majority of CoCrNi-based MEAs/HEAs. ● Precipitation strengthening, solid solution strengthening, and work-hardening can be introduced in CoCrNi MEAs easily through alloying and simple thermomechanical treatments. [ABSTRACT FROM AUTHOR]

The category and morphology of precipitates are essential factors in determining the mechanical behaviors of aluminum alloys. It is a great challenge to synthetically modulate multiple precipitates to simultaneously improve strength and ductility. In the present work, by optimizing the precipitations of the GP zone, θ'-approximant and θ' phase for an Al-Cu-Mn alloy, a high tensile strength of 585 MPa with large elongation of 12.35% was achieved through pre-deformation and aging. The microstructure evolution pattern was revealed by detailed characterizations of scanning electron microscopy and transmission electron microscopy. It was found that such high tensile strength of the samples was due to a combination of strengthening by the high density of dispersive fine precipitates and dislocations, and the high elongation to failure was primarily attributed to the multimodal precipitates and elimination of precipitation-free zones along the grain boundaries. The strategy proposed here is a promising way of preparing ultra-strong Al-Cu-Mn alloys. [ABSTRACT FROM AUTHOR]

Eutectic high entropy alloys (EHEAs) exhibit excellent mechanical properties in the as-cast condition. In this paper, Mo element was chosen to further strengthen the EHEAs by solid solution strengthening. The microstructures, phase compositions and mechanical properties of Co30Cr10Fe10Al18Ni32 − xMox (x = 0, 1, 2, 3) alloys were investigated. It was found that Mo acts as a solid solution strengthening element in the face-centered cubic (FCC) and body-centered cubic (BCC) phases. Meanwhile, Mo can promote the formation of the primary BCC phase. Among all alloys, the alloy with Mo (x = 2) has the highest fracture tensile strength of 1250 MPa and the acceptable elongation of 14%. [ABSTRACT FROM AUTHOR]

A novel Ti 41 V 27 Hf 13 Nb 13 Zr 6 refractory high-entropy alloy (RHEA) with an excellent fracture elongation of 30 % at a high strength level of 986 MPa was successfully fabricated. We discovered that kinking induced plasticity, involving successive stages of dislocation arrangement, pre-kinking, and the coalescence of multiple kink bands. The soft character of kinking originated from the degraded dislocation density within the kink bands. As such, the interplay between strain hardening caused by dislocation accumulation and the softening effect due to kink bands led to a plateau-type engineering stress-strain curve to large strains. These findings provide a novel design pathway to achieve ductile RHEAs via deformation kinking. • Kinking induced plasticity by stress relaxation and crystal reorientation in a Ti 41 V 27 Hf 13 Nb 13 Zr 6 refractory high-entropy alloy. • Kink formation was attributed to successive stages of dislocation arrangement, pre-kinking, and the coalescence of multiple kink bands. • The combined effects of simultaneous dislocation multiplication and deformation kinking jointly maintained tensile ductility even at gigapascal stresses. [ABSTRACT FROM AUTHOR]

The large amounts of data in eutectic high-entropy alloys (EHEAs) provide the opportunity for a rapid design of superior high-entropy alloys (HEAs). In this letter, we proposed a strategy to screen high-performance supersaturated HEAs based on the existing EHEAs with superior properties. The designed HEAs of supersaturated terminal solid solutions possess unique characteristics. On the one hand, the as-cast alloys exhibited primary single-phase dendrites/grains with maximum solid solution hardening and minor interdendritic/intergranular second phases as modifiers. On the other hand, the maximum saturation enabled the highest volume fraction of precipitates during aging. Taking advantage of these characteristics, high strength and ductility were achieved in the designed HEAs. These findings can accelerate the exploration of supersaturated HEAs with superior properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] A series of fcc structured equiatomic solid solutions were designed. [•] The solid solution limit in multi-component equiatomic alloys was explored. [•] Topological instability sets the solid solution limit. [•] Decomposition occurs when the lattice strain reaches a critical value of 0.018. [ABSTRACT FROM AUTHOR]

• A high density of multi-scale annealing twins was achieved in LPBF Ni 35 Co 35 Cr 25 Ti 3 Al 2 MEA. • The multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). • The positive effects of the multi-scale annealing twins on plastic deformation were discussed. • The critical relevance of cellular structures in influencing the nucleation behavior of annealing twins was elucidated for the first time. Coherent twin boundaries (CTBs) are internal planar defects that offer a promising pathway for designing advanced metallic materials with superior strength-ductility synergy. However, incorporating nanoscale CTBs into additive manufacturing (AM) microstructures is highly challenging without severe plastic deformation. Here, by utilizing the intrinsic cellular structures in AM alloys, we for the first time achieved a high density of multi-scale annealing twins in a laser powder bed fusion (LPBF) Ni 35 Co 35 Cr 25 Ti 3 Al 2 medium-entropy alloy. These multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). We reveal that the AM-induced cellular structures, decorated with entangled dislocations and Ti segregation at the cellular boundaries, facilitate the abundant nucleation of multi-scale annealing twins through interactions with migrating recrystallization boundaries. Additionally, the cellular precipitation networks enhance the thermal stability of nanoscale annealing twins. Frequent dislocation-TB interactions during deformation contribute to superior strain hardenability and thus good ductility. Synergized multiple strengthening mechanisms, i.e., boundary strengthening, precipitation strengthening, and dislocation strengthening, are responsible for the excellent strength. Our present findings advance the design of AM microstructures by harnessing the beneficial effects of cellular structures and provide valuable guidance for developing alloys with exceptional mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) have attracted considerable interest due to their elevated melting points and remarkable softening resistance. Nevertheless, the ambient-temperature brittleness and inadequate high-temperature oxidation resistance commonly limit the application of the body-centered-cubic (BCC) RHEAs. In this study, we achieved a Ti 41 V 27 Hf 11.5 Nb 11.5 Cr 3 Al 6 RHEA with a desirable yield strength of ∼1178 MPa and tensile ductility of ∼19.5 %. Exploring the underlying mechanisms, we demonstrated that Cr and Al alloying induced a nanoscale spinodal structure and generated a significant lattice misfit, resulting in a notable strengthening effect and pinning behavior. Meanwhile, dislocation configurations involving loops and cross slips were stimulated by pinning, serving a reliable strain-hardening capability to large strains. Significantly, Cr and Al alloying improved oxidation resistance and prevented severe spallation at high temperatures by forming protective oxide layers. These results provide opportunities to design novel RHEAs. [Display omitted] [ABSTRACT FROM AUTHOR]

Eutectic high-entropy alloys (EHEAs), as a sub-group of high-entropy alloys (HEAs), are becoming a new research hotspot in the metallic materials community because of their excellent castability, fine and uniform microstructures even in the as-cast state, high strength, and good ductility. Some of the EHEAs have shown promising potentials for industrial applications. Here, the history, interesting solidification microstructure and mechanical properties, and the design strategy of EHEAs are reviewed, and their future prospects are outlined. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The multicomponent L1 2 phase in high entropy alloys (HEAs) has shown excellent thermal stability. However, the understanding of its intrinsic origins is limited to the Lifshitz-Slyozov-Wagner (LSW) theory. In the present study, we investigate the influence of lattice misfit, which is not considered in LSW theory, on the coarsening kinetics of the multicomponent L1 2 phase. Different from that in most traditional alloys, the coarsening constant of multicomponent L1 2 particles decreases with the increasing lattice misfit in HEAs. This finding provides a new view for understanding the sluggish coarsening kinetics of L1 2 phase in HEAs. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The increased excess entropy in face-centered-cubic high entropy alloys is confirmed by quantitatively measuring heat capacities of pure Ni together with equiatomic NiCo, NiCoCr, and NiCoFeCr alloys with increasing configurational entropy. Surprisingly, the incredible excess entropy in the NiCoFeCr alloy can be even up to 0.9R, much larger than that in traditional alloys. The temperature-dependent measurement of the excess entropy indicates the major contribution of lattice vibrations. The excess magnetic entropy dominates in the temperature of 300 to 1000 K. The abnormal excess entropy reveals extraordinary lattice dynamic effects in high entropy alloys, which is a new feature in these alloys. The significant excess entropy at lower temperatures and their subtle shifts at high temperatures. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Precipitation strengthening is one of the most promising mechanisms to develop high-performance high entropy alloys (HEAs). However, the design of a reinforcing phase with an excellent strengthening effect is still one of the most pivotal challenges. In the present study, a design strategy based on overall valence electron concentration (OVEC) is developed, and a coherent D0 22 superlattice (noted as γ″ phase) with superior strengthening effect is designed. The newly developed γ″ phase is systematically characterized using transmission electron microscope and atom probe tomography. Differentiating from the traditional Ni 3 Nb γ″ phase, the present high-entropy γ″ phase contains ∼7.7% Co and follows the (Ni,Co,Cr,Fe) 3 (Nb,Fe) stoichiometry. Three γ″ phase variants are observed with crystallographic orientation relationships of [001] γ″ //<001> γ and (001) γ″ //{100} γ. The lenticular γ″ particles with small volume fraction (7%) causes a significant yield strength increase (670 MPa) and ductility retention (40%), resulting in excellent yield strength-ductility combination. The excellent strengthening effect of the γ″ phase is attributed to both ordering strengthening and coherency strengthening. The present study proposes a new design strategy of precipitates and develops a superior reinforcing phase for HEAs. These findings will not only promote the development of precipitation-hardened HEAs but deepen the fundamentals of precipitates design for other complex concentrated alloys as well. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Multi-component alloys with good mechanical properties and casting liquidity have become a hotspot in the materials field. Typically, the addition of minor metal elements plays a vital role in strengthening the mechanical properties. However, doping metalloid elements such as Si into multi-component alloys is also an effective method to enhance the mechanical properties. In the present study, the effect of Si (0 ∼ 4 at%) on the microstructure and mechanical properties was investigated within both as-cast and thermal mechanical treatment states. In as-cast state, all 4 alloys exhibited dendrites and interdendrites structure. The fine structure enhanced tensile strength for Si1 and improved ductility for Si2. Once the Si content reached 4 at%, both the strength and ductility dropped dramatically. Phase selective recrystallization and aging greatly increased the tensile strength and ductility simultaneously. The alloys with addition of Si had similar mechanical properties after thermal mechanical treatment process. Si2 after recrystallization and aging was considered a promising candidate for further application with a yield strength of 960 MPa, tensile strength of 1463 MPa and fracture strain of 20.5%. This work provided a new prospect to design multi-component alloys with nonmetallic elements, which may be applied to wear, corrosion and oxidation resistance fields. • The effects of metalloid Si on the microstructure and mechanical properties of Fe 36 Ni 36 Cr 10 Mo 1 Al 17−X Si X was investigated. • The addition of Si enhanced tensile strength to 1305 MPa for Si1 and improved ductility to 24.8% elongation for Si2. • Si2-R-A showed mechanical properties with yield strength of 960 MPa, tensile strength of 1463 MPa and ductility of 20.5%. [ABSTRACT FROM AUTHOR]

In this work, TaTiNbZr refractory high entropy alloy (RHEA) films constructed with nano-crystalline and amorphous composite structures were irradiated by helium (He) plasma with a fixed flux of 5 × 1022 m−2·s−1 under bias-voltage driven plasma energy (0–70 eV) to systematically explore the evolution of morphological modification and mechanical properties. The results indicated that the RHEA exhibited composite structures after He plasma irradiation, and the irradiation-enhanced surface blisters were strongly dependent on He plasma energy. After exposure to He plasma, the size and density of blisters on the surface of RHEA films gradually increased with the enhancement of plasma energy, these blisters originated from the formation of bulges underneath the surface which were induced by the large-sized bubbles. Some blister bursts were initiated at a critical energy of 50 eV (irradiation temperature was 600 K). Non-obvious superficial sputtering can be observed for the RHEA films irradiated at energy less than 50 eV. At the He plasma energy of 70 eV, cracks and abundant blister exfoliation were produced on the RHEA surface due to the synergistic effect of enhanced energy and irradiation temperature (650 K). Surface sputtering and the thermal diffusion-driven mass flow were induced by He plasma due to the sputtering threshold energies in Ti and Zr elements than that of Ta and Nb elements, which were responsible for the growth of fiber-like structures on the surface of RHEA film as the energy was fixed at 70 eV. Moreover, the maximum hardening ratio of 21.4% was revealed from the TaTiNbZr RHEA nano-film irradiated at plasma energy of 50 eV, the role of plasma energy on the evolution of mechanical properties, and the corresponding mechanisms in response to irradiation damage were also discussed in detail. [ABSTRACT FROM AUTHOR]

Face-centered-cubic (FCC) Multi-principal element alloys (MPEAs) have attracted intensive scientific research interest due to their excellent fracture toughness and ductility. Still, the strengths of single-phase MPEAs are unsatisfactory. Although great progress has been made by utilizing multiple strengthening mechanisms, it remains challenging to take advantage of large-atom solutes and nano-precipitates simultaneously because solutes always partition into the precipitates. In the present work, we successfully achieved an effective combination of solid solution strengthening and precipitation hardening in the NiCrFeWTiAl multi-principal element alloys. Our experimental results showed that W is partitioned into the FCC matrix, while Ti and Al tend to exist in the L1 2 phase. This controlled elemental partitioning leads to a good combination of solid solution strengthening and precipitation hardening effects and results in good tensile properties at temperatures from 25 ℃ to 760 ℃. The strengthening mechanisms were revealed based on the quantified microstructure analysis. The solid solution hardening of all the solute atoms contributes ∼140 MPa in total, but W mainly contributes to solid solution hardening, and L1 2 precipitates enhance the yield strength by ∼330 MPa through ordering strengthening. • The NiCrFeWTiAl MPEAs efficiently combine the solid solution strengthening and precipitation hardening. • The W partitioned into the FCC matrix mainly leads to solid solution hardening. • The L1 2 phase which enriched in Ti and Al enhances the yield strength through the ordering strengthening mechanism. • The effect of Cr on the microstructure and mechanical properties was demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • γ′′ precipitation behaviors and their impacts on mechanical properties were systematically investigated. • The strengthening and deformation mechanical in Nb-alloyed MEA with different microstructures were investigated. • The heterogeneous lamellar grain coupling with dual-precipitation structure in this Nb-alloyed MEA brought out superior strength-ductility synergy properties. In present work, a novel γ′′-strengthened Nb-alloyed medium-entropy alloy (MEA) was successfully fabricated and systematically investigated. Our results evidence that the γ′′ phase brings out significant precipitation hardening effect (∼10.2 %volume fraction contributes ∼ 685 MPa strength enhancement). The metastable γ′′ phase could abnormally transform to ε phase, and the morphology and distribution of ε phase shows great impacts on mechanical properties. A hetero-lamellae grain coupling with dual-precipitation (HLG + dual-P) structure was successfully constructed in this Nb-alloyed MEA, which could effectively combine precipitation hardening and hetero-deformation induced (HDI) hardening effects. Deformation characters investigations reveals that the absence of mechanical twinning in γ′′-strengthened MEA originates from the improved critical twinning stress related to the fine dislocation source size and the difficulty of high-energy complex SFs reordering. The combination of massive stacking-faults, Lomer-Cottrell locks and dynamically reinforced HDI hardening contribute to the excellent ductility and work-hardening capacity at high-level strength in the HLG + dual-P structural alloy. Our work provides a useful insight and helpful guidance for developing high-performance precipitation-hardened multi-principal element alloys. [ABSTRACT FROM AUTHOR]

Precipitation hardening is used as a powerful strengthening pathway to tailor the mechanical properties of traditional alloys. However, in refractory multi-principal element alloys (RMPEAs), the precipitates with remarkable strengthening effect are relatively less explored. Here, we report novel precipitation hardened body-centered-cubic (BCC) TiVNb RMPEAs through doping surplus boron. 2000 ppm (0.2 wt%) boron doping leads to TiB precipitates, which can enhance the yield strength of TiVNb by ∼350 MPa. Orowan strengthening caused by TiB precipitates serves as the primary strengthening mechanism compared to non-boron alloys. Due to boron doping, the dislocation-mediated deformation transfers from planar-slip to cross-slip and thus avoids stress concentration caused by high-density geometrically necessary dislocation. The excellent strengthening effect and tuned deformation mechanisms led to an optimal RMPEA with a yield tensile strength of ∼972 MPa and an elongation of ∼12%. This work demonstrates that TiB is an efficient precipitate in BCC RMPEAs, which is constructive for the development of precipitation hardened RMPEAs. [Display omitted] • Surplus boron doping is put forward to produce stable TiB precipitates in the TiVNb alloy. • Nanoscale TiB precipitates can increase the yield tensile strength by 35.7% via Orowan strengthening. • The cross slip in the TiVNbB RMPEA led to an undamaged elongation of ∼12%. [ABSTRACT FROM AUTHOR]

With excellent compressive mechanical properties, FeNiCrAl medium entropy alloys with multi-principal components have attracted extensive attention in recent years. However, the limited tensile ductility of FeNiCrAl medium entropy alloys is the bottleneck for their industrial applications. In this work, dual phases of FCC + B2 and BCC + B2 were modulated in FeNiCrAl medium entropy alloys for excellent tensile behaviors. In the as-cast state, the tensile yield strength and ultimate tensile strength are 1140 MPa and 1423 MPa, respectively, with a uniform elongation of 6.0%. • As-cast dual phases FeNiCrAl medium entropy alloys are designed for excellent tensile behavior. • Dual phases of FCC+B2 and BCC+B2 are modulated by changing the valence electron concentration via the ratio of Fe/Ni. • Fe 47 Ni 26 Cr 10 Al 17 alloy has a fine nanostructure with BCC+B2 dual phases. • As-cast Fe 47 Ni 26 Cr 10 Al 17 alloy shows yield strength of 1140 MPa and uniform elongation of 6.0%. [ABSTRACT FROM AUTHOR]

High performance precipitation strengthened high-entropy alloys (HEAs) can be prepared by concurrent recrystallization and precipitation in the process of aging at intermediate temperatures after rolling. Generally, the homogenized samples are subjected to rolling before aging, where the effects of initial grain structure before rolling on the concurrent recrystallization and precipitation are overlooked. In this study, we revealed the inherited effect of initial grain on the concurrent recrystallization and precipitation in Co 37 Cr 20 Ni 37 Ti 3 Al 3 HEA. The heredity of grain homogeneity to the initial grain structure was revealed, where the initial grain structure influences the homogeneity of strain distribution during rolling and influences the recrystallization in the subsequent aging. Moreover, the inherited effect of the initial grain structure also influences the precipitation behavior. TEM characterization confirmed that the lamellar precipitation decreases, while spherical precipitation increases with the increase of the initial grain size. By tailoring the initial grain size, the strength and ductility of Co 37 Cr 20 Ni 37 Ti 3 Al 3 alloy were simultaneously improved. The present study provides a good understanding of the concurrent recrystallization and precipitation in HEAs. [ABSTRACT FROM AUTHOR]

Hierarchical interfaces and nanometer grain boundaries (GBs) were synchronously designed inside the homogeneous Al 1.5 CoCrFeNi high entropy alloy (HEA) nano-multilayered films, in which each lamellae was composed of nano-crystals to construct helium (He) ion radiation-tolerant materials used for future advanced nuclear-energy system. The depth profile of He behavior and phase-structure evolution in the irradiated [Al 1.5 CoCrFeNi (10 nm)]30 and [Al 1.5 CoCrFeNi (30 nm)]10 nano-multilayered films were investigated systematically. Results indicated that the He bubble size in multilayered film exhibited a reduction tendency and a wide distribution feature as the individual-thickness increased from 10 nm to 30 nm, demonstrating inverse results with previous heterogeneous-interface modeling. Reduced bubble pressures were identified in the two kinds of nano-multilayered HEA films, indicating that the coexistence of nanocrystals and homogeneous-interfaces was beneficial to manage He distribution and prolonged bubble growth effectively by tailoring each-lamellae size in these two kinds of multilayered Al 1.5 CoCrFeNi HEA films. Partial phase transformation from body-centered-cubic (BCC) to face-centered-cubic (FCC) structure was induced through promoting the structural evolution between the irradiation-induced amorphous regions and compositional reorganization in these nano-multilayered HEA films upon irradiation. The interfaces and GBs promoted the annihilation of these defects and further facilitated the self-healing behavior. Such hierarchical-interface in the HEA provides a novel strategy for the effective He entrapment in improving radiation tolerance and a potential possibility of real-application. • Hierarchical-interfaces and nanometer grain boundaries were designed for managing helium distribution in nano-multilayered Al 1.5 CoCrFeNi HEA films. • The reduced pressure inside helium bubble was effectively tuned by tailoring the each-lamellae size. • The phase structure evolution was explained by irradiation-induced amorphous regions and compositional reorganization. [ABSTRACT FROM AUTHOR]

• A coupled CA-LB model incorporating rapid solidification features is developed. • The PDAS increases as the cooling rate decreases and the shear flow increases. • Shear flows facilitate the dendrite elimination by promoting competitive growth. • The effects of shear flow on PDAS become stronger as the cooling rate increases. The growth of columnar dendrites during rapid directional solidification of IN718 alloy in the presence of shear flows is simulated by using a coupled cellular automaton-lattice Boltzmann (CA-LB) model. The developed CA-LB model is benchmarked by the mesh independency of the steady-state dendrite growth velocity and the primary dendrite arm spacing (PDAS) under different cooling rates. The CA-LB model is then applied to simulate the columnar dendrite growth under different shear flows and cooling rates in the conditions of rapid solidification. The values of PDAS under different conditions are determined from the simulation results, and are correlated with the shear flow rate (U sh) and cooling rate (CR). A unified fitting formula is developed to represent the effects of U sh and CR on the evolution of PDAS. The PDAS is found to decrease with CR increasing, but increase with U sh increasing. Moreover, it is revealed that the influence of U sh on PDAS becomes stronger as CR increases. [ABSTRACT FROM AUTHOR]