Chemical Short-Range Ordering in Nanoprecipitates Modulates Planar Faults to Enhance Mechanical Properties

Nanoprecipitates strengthen metallic materials by impeding dislocation motion, but they often compromise ductility. This study introduces a novel strategy to address this challenge by incorporating atomic-scale chemical heterogeneity within nanoprecipitates. For the first time, pronounced short-range ordering (SRO) within L12-ordered precipitates of the Co40Ni30Cr20Al5Ti4Ta1 multi-principal element alloy is observed and confirmed, with its formation mechanism elucidated via density functional theory. Experimental and computational results show that the unique atomic configuration reshapes the energy landscape of planar defects, enhancing the strength and work-hardening capacity. The SRO structure elevates the critical shear stress for dislocation-mediated precipitate shearing while reducing the formation energy of superlattice intrinsic stacking faults, thereby promoting nucleation site formation. This work pioneers a method for modulating atomic-scale heterogeneity within ordered structures, advancing high-performance material design.

Achieving High Damping Capacity in Oxygen-Enhanced BCC Zr-Hf-Ti-Nb Multi-Principal-Element Alloys with Low Young's Modulus

Multi-principal-element alloys (MPEAs) have gained widespread popularity due to the efficient synergetic regulation of mechanical and functional properties in a huge compositional space. Here, novel O-enhanced BCC Zr-Hf-Ti-Nb MPEAs with prominent mechanical and damping properties are developed by the composition formula of (Zr,Hf,Ti)15Nb3. The Zr14TiNb3 and Zr8Hf6TiNb3 alloys possess low BCC-β structural stability. While the Zr8Hf4Ti3Nb3 alloy has a much higher BCC-β stability, as evidenced by the fact that only few α'' and ω precipitates appear in 1.8 at% oxygen-added alloy. This alloy exhibits an optimal mechanical property with a higher yield strength (σYS = 1000 MPa) and larger ductility (ε = 15.1%), which is ascribed to the formation of O-rich clusters in BCC matrix. Moreover, these oxygen-free and -added alloys exhibit an excellent damping capacity due to their low Young's modulus (E < 70 GPa), as exemplified with a peak value of (tanδ)max = 0.02 for 1.8 at% oxygen-added alloy. Notably, the damping characteristics are prominent over a wide temperature range (550-800 K), which derives from the occurrence of multiple separated oxygen-rich clusters. The present findings provide an avenue to enhance mechanical and functional performances of high-temperature damping alloys.

Tuning Internal Stress in Metals with Bimodal Particles for Exceptional Strength and Ductility

Microstructural heterogeneity and associated nonuniform internal stress in metallic materials are crucial for achieving excellent mechanical properties. However, general methods for controlling such heterogeneity remain scarce. Metal matrix composites are intrinsically heterogeneous materials with tunable microstructures. Here, we developed a micron/nano-bimodal reinforcement structure that optimizes internal stress distribution, which not only reduces local stress concentration at interfaces but also facilitates the extensive activation of nonpreferential slip systems in alloys. As a result, the representative Al2024 alloy exhibits an extraordinary true tensile strength of ∼750 MPa and impressive ductility (with elongation-to-failure exceeding 10%). Stress delocalization at interfaces and strong local dislocation interactions are synchronously prompted through internal stress tuning at the nanoscale, with the optimized size of fine particles being ∼1/10 of coarse reinforcing particles, contributing to sustained dislocation accumulation and, consequently, large tensile ductility.

Facile synthesis of Ir-based high-entropy alloy nanomaterials for efficient oxygen evolution electrocatalysis

High-entropy alloy (HEA) nanomaterials have emerged as promising candidates as oxygen evolution reaction (OER) electrocatalyst to overcome the existing issues of the sluggish reaction kinetics and poor stability. In this study, IrxRuCoCuNi HEA three-dimensional-nanoframeworks (3DNF) are prepared using a scalable approach-the spray-drying technique combined with thermal decomposition reduction (SD-TDR). The optimized catalyst, Ir2RuCoCuNi, demonstrates superior OER performance, with an overpotential of 264 mV at 10 mA cm-2 and a Tafel slope of 47 mV dec-1, considerably surpassing the catalytic activity of commercial IrO2. Electrochemical data reveal high electron transfer efficiency and a significant electrochemically active surface area (ECSA), attributed to its 3DNF porous structure and favorable surface self-reconstruction into (oxy)hydroxides during the OER. While increasing Ir content enhances catalytic activity, economic analysis highlights compositions with reduced Ir content, such as IrRu2CoCuNi and IrRuCo2CuNi, as cost-effective alternatives for practical applications. These findings underscore the potential of HEA 3DNFs for industrial-scale electrocatalysis and provide insights into balancing performance and cost for next-generation OER catalysts.

Highly printable, strong, and ductile ordered intermetallic alloy

Ordered intermetallic alloys are renowned for their impressive mechanical, chemical, and physical properties, making them appealing for various fields. However, practical applications of them have long been severely hindered due to their severe brittleness and poor fabricability. It is difficult to fabricate such materials into components with complex geometries through traditional subtractive manufacturing methods. Here, we proposed a strategy to solve these long-standing issues through the additive manufacturing of chemically complex intermetallic alloy (CCIMA) based on laser powder bed fusion (LPBF). The developed CCIMA exhibits good printability, enabling a crack-free microstructure with a low porosity of 0.005%. More importantly, a good combination of high tensile strength (~1.6 GPa) and large uniform elongation (~35%) can be achieved, which has not been reported in the existing additive-manufactured alloys. Such properties are attributed to the structural and chemical features of highly ordered superlattice grain decorated with disordered interfacial nanolayer, as well as dynamic evolutions and interactions of multiple dislocation substructures. These findings could provide references for developing high-performance intermetallic alloys and accelerating their practical applications.

Ductilization of 2.6-GPa alloys via short-range ordered interfaces and supranano precipitates

Higher strength and higher ductility are desirable for structural materials. However, ultrastrong alloys inevitably show decreased strain-hardening capacity, limiting their uniform elongation. We present a supranano (<10 nanometers) and short-range ordering design for grain interiors and grain boundary regions, respectively, in fine-grained alloys based on vanadium, cobalt, and nickel, with additions of tungsten, copper, aluminum, and boron. The pronounced grain boundary-related strengthening and ductilization mechanism is realized through segregation of the short-range ordering near the grain boundary. Furthermore, the supranano ordering with a larger size has an enhanced pinning effect for dislocations and stacking faults, multiplied and accumulated in grain interiors during plastic deformation. These mechanisms promote continuously increased flow stress until fracture of the alloy at 10% strain with 2.6-gigapascal tensile stress.

Electronic structure modulation of ultrathin PtRuMoCoNi high-entropy alloy nanowires for boosting peroxidase-like activity and sensitive colorimetric determination of isoniazid and hydrazine

Self-supported ultrathin PtRuMoCoNi high-entropy alloy nanowires (HEANWs) were synthesized by a one-pot co-reduction method, whose peroxidase (POD)-like activity and catalytic mechanism were elaborated in detail. As expected, the PtRuMoCoNi HEANWs showed excellent POD-like activity. It can quickly catalyze the oxidization of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue OXTMB through decomposition of H2O2 to superoxide radicals. Notably, isoniazid and hydrazine effectively scavenge the as-produced superoxide radicals and reduce the blue OXTMB, showing high reduction ability and antioxidant property. Thus, the PtRuMoCoNi HEANW-derived colorimetric method was developed for determination of isoniazid and hydrazine, which exhibited the linear ranges of 1.5 to 50 μM and 25 to 200 μM coupled with the lower detection limits of 2.3 and 12.6 μM for isoniazid and hydrazine, respectively. The excellent analytical performance mainly results from the synergistic catalytic effect of the multiple metals and distinctive ultra-thin nanowires. This work provides a simple and rapid colorimetric method for the determination of isoniazid and hydrazine in actual samples.

A Complex Concentrated Alloy with Record-High Strength-Toughness at 77 K

High strength and large ductility, leading to a high material toughness (area under the stress-strain curve), are desirable for alloys used in cryogenic applications. Assisted by domain-knowledge-informed machine learning, here a complex concentrated Fe35Co29Ni24Al10Ta2 alloy is designed, which uses L12 coherent nanoprecipitates in a high volume fraction (≈65 ± 3 vol.%) in a face-centered-cubic (FCC) solid solution matrix that undergoes FCC-to-body-centered-cubic (BCC) phase transformation upon tensile straining. Unlike FCC-to-BCT phase transformation involving brittle carbon-enriched martensite, the BCC martensite in this alloy does not cause brittleness at 77 K. The Fe35Co29Ni24Al10Ta2 multi-principal element alloy achieves a high yield strength ≈1.4 GPa, a high work hardening rate >4 GPa, an ultimate tensile strength ≈2.25 GPa, and a large uniform elongation ≈45%, leading to record-high material toughness compared with previous cryogenic alloys such as 316L series stainless steels and recent high-entropy alloys. The nanoprecipitates with nanoscale spacing (≈7.5 nm), apart from serving as dislocation obstacles for strengthening and dislocation sources for sustainable ductility, also undergo deformation twinning. Taken together, these mechanisms are found to be highly effective in strengthening and strain hardening upon tensile straining at liquid nitrogen temperature. These findings demonstrate how to effectively integrate strengthening mechanisms to synergize superior mechanical properties in special-purpose alloys.

VASE: A High-Entropy Alloy Short-Range Order Structural Descriptor for Machine Learning

The short-range order (SRO) structure in high-entropy alloys (HEAs) is closely associated with many properties, which can be studied through density functional theory (DFT) calculations. Atomic-scale modeling and calculations require substantial computational resources, and machine learning can provide rapid estimations of DFT results. To describe SRO information in HEAs, a new descriptor based on Voronoi Analysis and Shannon Entropy (VASE) is proposed. Based on Voronoi analysis, the Shannon entropy is introduced to directly characterize atomic spatial arrangement information except for composition and atomic interactions, which is necessary for describing the disorder atomic occupancy in HEAs. The new descriptor is used for predicting the formation energy of FeCoNiAlTiCu system based on machine learning model, which is more accurate than other descriptors (Coulomb matrices, partial radial distribution functions, and Voronoi analysis). Moreover, the model trained based on VASE descriptors exhibits the best predictive performance for unrelaxed structures (24.06 meV/atom). The introduction of Shannon entropy provides an effective representation of atomic arrangement information in HEAs, which is a powerful tool for investigating the SRO phenomena.

A one-step fabrication of soft-magnetic high entropy alloy fiber with excellent strength and flexibility

Soft-magnetic fibers (SMFs) play a crucial role in energy conversion, transmission, and storage within electronic devices. However, conventional SMFs have poor plasticity and are therefore difficult to withstand long-term tensile, torsional, and shear deformation. A high fraction of grain boundaries could improve plastic deformability of conventional SMFs, but deteriorates the coercivity. This severely limits their applications in flexible electronics and multifunctional components. Herein, we propose a strategy to overcome this dilemma, which is realized by coarsening the grains of a Fe34Co29Ni29Al3Ta3Si2 high entropy alloy (HEA) fiber containing ordered coherent nanoprecipitates with small lattice misfit via a simple one-step in-rotating-water spinning method. This allows to reduce domain wall pinning and improve dislocation mobility. The resultant micron-diameter soft-magnetic HEA fiber has a tensile strength of 674 MPa at 23% elongation, a low coercivity of 8.1 Oe, a moderate magnetization of 116 emu/g at 10 kOe and a high Curie temperature of 770 K.

Twinning and 9R Phase Transition Mediated Extraordinary Cold-drawn Deformability in NiCoCrFeMo High-Entropy Alloy

The production and application of materials are evolving towards the low-dimensional micro-nano scale. Nevertheless, the fabrication of micron-scale alloy fibers remains a challenge. Herein, a novel Ni-Co-Cr-Fe-Mo high-entropy alloy (HEA) fiber with a cold-drawn reduction rate of 99.9995% and a strain (ɛ) of 12.19 is presented without requiring intermediate annealing. The exceptional deformation strain of 11.62 within the fiber leads to extraordinary tensile strengths of 2.8 GPa at room temperature and 3.6 GPa at 123 K. The in-depth investigation of the microstructure of fibers has revealed the cold drawing deformation mechanisms mediated by the synergistic effects of plane defects. Specifically, various geometrically necessary dislocation interfaces, such as dislocation walls and microbands, along with deformation twins and long-period 9R structures, form in response to external stress when ɛ≤2.7. As the strain increases, the saturated layered structure emerges and progressively evolves into a 3D equiaxed crystal. Moreover, the formation and evolution of the 9R structure (i.e., the migration of incoherent twin boundaries), coupled with the interaction of partial dislocations and the role of deformation twins, are crucial factors determining the fiber's plastic response. This work provides a novel approach to discovering new high-strength metallic fibers with excellent deformability through plane defects engineering.

Formation of hierarchically structured martensites in pure iron with ultrahigh strength and stiffness

Strong steels are primarily fabricated by introducing spatial obstacles (e.g., stacking faults and precipitates) that inhibit dislocation slips under stress to achieve high strength. However, for most low-carbon steels, such obstacles are difficult to form mainly because the martensitic transition is kinetically unfavorable by conventional methods, which precludes the attainment of high-strength materials in these steels with low solute contents. Here, we report an innovative high-pressure preparation of martensitic pure Fe with involving nano-effect, which leads to the formation of ultrastrong bulk iron with exceptionally high yield strength, ultimate strength, and hardness of 2.9 GPa, 3.7 GPa, and 9.0 GPa, respectively, exceeding those of high-speed steels. Such extraordinary mechanical properties are closely attributed to its high-density martensites with unique multiscale hierarchical structures formed due to complex phase transitions under pressure.

Molten Aluminum-Induced Corrosion and Wear-Resistance Properties of ZrB2-Based Cermets Improved by Sintering-Temperature Manipulation

During the hot dip aluminum plating process, components such as sinking rollers, pulling rollers, and guide plates will come into long-term contact with high-temperature liquid aluminum and be corroded by the aluminum liquid, greatly reducing their service life. Therefore, the development of a material with excellent corrosion resistance to molten aluminum is used to prepare parts for the dipping and plating equipment and protect the equipment from erosion, which can effectively improve the production efficiency of the factory and strengthen the quality of aluminum-plated materials, which is of great significance for the growth of corporate profits. With AlFeNiCoCr as the binder phase and ZrB2 as the hard phase, ZrB2-based ceramic composites were prepared by spark plasma sintering (SPS). SEM, EDS and XRD were used to characterize the microstructure and properties of the sintered, corroded, and abraded material samples. The density, fracture toughness, corrosion rate and wear amount of the composite material were measured. The results show that ZrB2-AlFeNiCoCr ceramics have compact structure and excellent mechanical properties, and the density, hardness and fracture toughness of ZrB2-AlFeNiCoCr increase with the increase in sintering temperature. However, when the composite material is at 1600 °C, the relative density of the sintering at 1600 °C decreases due to the overflow of the bonding phase. Therefore, when the sintering temperature is 1500 °C, the high entropy alloy has the best performance. The average corrosion rate of ZrB2-1500 at 700 °C liquid aluminum is 1.225 × 10-3 mm/h, and the wear amount in the friction and wear test is 0.104 mm3.

Phase Engineering of High-Entropy Alloy for Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Directly electrochemical conversion of nitrate (NO3 -) is an efficient and environmentally friendly technology for ammonia (NH3) production but is challenged by highly selective electrocatalysts. High-entropy alloys (HEAs) with unique properties are attractive materials in catalysis, particularly for multi-step reactions. Herein, we first reported the application of HEA (FeCoNiAlTi) for electrocatalytic NO3 - reduction to NH3 (NRA). The bulk HEA is active for NRA but limited by the unsatisfied NH3 yield of 0.36 mg h-1 cm-2 and Faradaic efficiency (FE) of 82.66 %. Through an effective phase engineering strategy, uniform intermetallic nanoparticles are introduced on the bulk HEA to increase electrochemical active surface area and charge transfer efficiency. The resulting nanostructured HEA (n-HEA) delivers enhanced electrochemical NRA performance in terms of NH3 yield (0.52 mg h-1 cm-2) and FE (95.23 %). Further experimental and theoretical investigations reveal that the multi-active sites (Fe, Co, and Ni) dominated electrocatalysis for NRA over the n-HEA. Notably, the typical Co sites exhibit the lowest energy barrier for NRA with *NH2 to *NH3as the rate-determining step.

Effect of Coherent Nanoprecipitate on Strain Hardening of Al Alloys: Breaking through the Strength-Ductility Trade-Off

So-called strength-ductility trade-off is usually an inevitable scenario in precipitation-strengthened alloys. To address this challenge, high-density coherent nanoprecipitates (CNPs) as a microstructure effectively promote ductility though multiple interactions between CNPs and dislocations (i.e., coherency, order, or Orowan mechanism). Although some strain hardening theories have been reported for individual strengthening, how to increase, artificially and quantitatively, the ductility arising from cooperative strengthening due to the multiple interactions has not been realized. Accordingly, a dislocation-based theoretical framework for strain hardening is constructed in terms of irreversible thermodynamics, where nucleation, gliding, and annihilation arising from dislocations have been integrated, so that the cooperative strengthening can be treated through thermodynamic driving force ∆G and the kinetic energy barrier. Further combined with synchrotron high-energy X-ray diffraction, the current model is verified. Following the modeling, the yield stress σy is proved to be correlated with the modified strengthening mechanism, whereas the necking strain εn is shown to depend on the evolving dislocation density and, essentially, the enhanced activation volume. A criterion of high ∆G-high generalized stability is proposed to guarantee the volume fraction of CNPs improving σy and the radius of CNPs accelerating εn. This strategy of breaking the strength-ductility trade-off phenomena by controlling the cooperative strengthening can be generalized to designing metallic structured materials.

Controllable synthesis of high-entropy alloys

High-entropy alloys (HEAs) involving more than four elements, as emerging alloys, have brought about a paradigm shift in material design. The unprecedented compositional diversities and structural complexities of HEAs endow multidimensional exploration space and great potential for practical benefits, as well as a formidable challenge for synthesis. To further optimize performance and promote advanced applications, it is essential to synthesize HEAs with desired characteristics to satisfy the requirements in the application scenarios. The properties of HEAs are highly related to their chemical compositions, microstructure, and morphology. In this review, a comprehensive overview of the controllable synthesis of HEAs is provided, ranging from composition design to morphology control, structure construction, and surface/interface engineering. The fundamental parameters and advanced characterization related to HEAs are introduced. We also propose several critical directions for future development. This review can provide insight and an in-depth understanding of HEAs, accelerating the synthesis of the desired HEAs.

Clarifying the four core effects of high-entropy materials

High-entropy materials emerged as a field of research in 2004, when the first research on high-entropy alloys was published. The scope was soon expanded from high-entropy alloys to medium-entropy alloys, as well as to ceramics, polymers and composite materials. A fundamental understanding on high-entropy materials was proposed in 2006 by the 'four core effects' - high-entropy, severe-lattice-distortion, sluggish-diffusion and cocktail effects - which are often used to describe and explain the mechanisms of various peculiar phenomena associated with high-entropy materials. Throughout the years, the effects have been examined rigorously, and their validity has been affirmed. This Perspective discusses the fundamental understanding of the four core effects in high-entropy materials and gives further insights to strengthen the understanding for these effects. All these clarifications are believed to be helpful in understanding low-to-high-entropy materials as well as to aid the design of materials when studying new compositions or pursuing their use in applications.

Shearing brittle intermetallics enhances cryogenic strength and ductility of steels

Precipitates are crucial for crafting mechanically strong metallic materials. In this work, we report the dislocation cutting of B2 (ordered body-centered cubic) nanoprecipitates, typically considered nonshearable intermetallics, in a lightweight compositionally complex steel during cryogenic tensile loading. Shearing is enabled by the high strength level for dislocation glide within the austenitic matrix, attributed to the substantial strengthening from subnanoscale local chemical ordering zones and the pronounced solid solution strengthening from the multiprincipal elements in the matrix. This mechanism not only harnesses the intense strengthening and strain hardening provided by otherwise impenetrable brittle nanoprecipitates but also introduces ductility through their sequential shearing with ongoing deformation. Our steel thus showcases ultrahigh cryogenic tensile strength up to 2 gigapascal at a remarkable tensile elongation of 34%. This study reveals a new strategy for designing high-performance structural materials.

Ultrastrong and ductile medium-entropy alloys via hierarchical ordering

Long-range ordered phases in most high-entropy and medium-entropy alloys (HEAs/MEAs) exhibit poor ductility, stemming from their brittle nature of complex crystal structure with specific bonding state. Here, we propose a design strategy to severalfold strengthen a single-phase face-centered cubic (fcc) Ni2CoFeV MEA by introducing trigonal κ and cubic L12 intermetallic phases via hierarchical ordering. The tri-phase MEA has an ultrahigh tensile strength exceeding 1.6 GPa and an outstanding ductility of 30% at room temperature, which surpasses the strength-ductility synergy of most reported HEAs/MEAs. The simultaneous activation of unusual dislocation multiple slip and stacking faults (SFs) in the κ phase, along with nano-SF networks, Lomer-Cottrell locks, and high-density dislocations in the coupled L12 and fcc phases, contributes to enhanced strain hardening and excellent ductility. This work offers a promising prototype to design super-strong and ductile structural materials by harnessing the hierarchical ordered phases.

Nanostructured High Entropy Alloys as Structural and Functional Materials

Since their introduction in 2004, high entropy alloys (HEAs) have attracted significant attention due to their exceptional mechanical and functional properties. Advances in our understanding of atomic-scale ordering and phase formation in HEAs have facilitated the development of fabrication techniques for synthesizing nanostructured HEAs. These materials hold immense potential for applications in various fields including automobile industries, aerospace engineering, microelectronics, and clean energy, where they serve as either structural or functional materials. In this comprehensive Review, we conduct an in-depth analysis of the mechanical and functional properties of nanostructured HEAs, with a particular emphasis on the roles of different nanostructures in modulating these properties. To begin, we explore the intrinsic and extrinsic factors that influence the formation and stability of nanostructures in HEAs. Subsequently, we delve into an examination of the mechanical and electrocatalytic properties exhibited by bulk or three-dimensional (3D) nanostructured HEAs, as well as nanosized HEAs in the form of zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, or two-dimensional (2D) nanosheets. Finally, we present an outlook on the current research landscape, highlighting the challenges and opportunities associated with nanostructure design and the understanding of structure-property relationships in nanostructured HEAs.

Effect of Alloying Elements on the High-Temperature Yielding Behavior of Multicomponent γ'-L12 Alloys

The exceptional mechanical properties of Ni-based high entropy alloys are due to the presence of ordered L12 (γ') precipitates embedded within a disordered matrix phase. While the strengthening contribution of the γ' phase is generally accepted, there is no consensus on the precise contribution of the individual strengthening mechanisms to the overall strength. In addition, changes in alloy composition influence several different mechanisms, making the assessment of alloying conditions complex. Multicomponent L12-ordered single-phase alloys were systematically developed with the aid of CALPHAD thermodynamic calculations. The alloying elements Co, Cr, Ti, and Nb were chosen to complexify the Ni3Al structure. The existence of the γ' single phase was validated by microstructure characterization and phase identification. A high-temperature compression test from 500 °C to 1000 °C revealed a positive temperature dependence of strength before reaching the peak strength in the studied alloys NiCoCrAl, NiCoCrAlTi, and NiCoCrAlNb. Ti and Nb alloying addition significantly enhanced the high-temperature yield strengths before the peak temperature. The yield strength was modeled by summing the individual effects of solid solution strengthening, grain boundary strengthening, order strengthening, and cross-slip-induced strengthening. Cross-slip-induced strengthening was shown to be the key contributor to the high-temperature strength enhancement.

Overcoming strength-ductility tradeoff with high pressure thermal treatment

Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials.

Neural network kinetics for exploring diffusion multiplicity and chemical ordering in compositionally complex materials

Diffusion involving atom transport from one location to another governs many important processes and behaviors such as precipitation and phase nucleation. The inherent chemical complexity in compositionally complex materials poses challenges for modeling atomic diffusion and the resulting formation of chemically ordered structures. Here, we introduce a neural network kinetics (NNK) scheme that predicts and simulates diffusion-induced chemical and structural evolution in complex concentrated chemical environments. The framework is grounded on efficient on-lattice structure and chemistry representation combined with artificial neural networks, enabling precise prediction of all path-dependent migration barriers and individual atom jumps. To demonstrate the method, we study the temperature-dependent local chemical ordering in a refractory NbMoTa alloy and reveal a critical temperature at which the B2 order reaches a maximum. The atomic jump randomness map exhibits the highest diffusion heterogeneity (multiplicity) in the vicinity of this characteristic temperature, which is closely related to chemical ordering and B2 structure formation. The scalable NNK framework provides a promising new avenue to exploring diffusion-related properties in the vast compositional space within which extraordinary properties are hidden.

Chemical short-range disorder in lithium oxide cathodes

Ordered layered structures serve as essential components in lithium (Li)-ion cathodes1-3. However, on charging, the inherently delicate Li-deficient frameworks become vulnerable to lattice strain and structural and/or chemo-mechanical degradation, resulting in rapid capacity deterioration and thus short battery life2,4. Here we report an approach that addresses these issues using the integration of chemical short-range disorder (CSRD) into oxide cathodes, which involves the localized distribution of elements in a crystalline lattice over spatial dimensions, spanning a few nearest-neighbour spacings. This is guided by fundamental principles of structural chemistry and achieved through an improved ceramic synthesis process. To demonstrate its viability, we showcase how the introduction of CSRD substantially affects the crystal structure of layered Li cobalt oxide cathodes. This is manifested in the transition metal environment and its interactions with oxygen, effectively preventing detrimental sliding of crystal slabs and structural deterioration during Li removal. Meanwhile, it affects the electronic structure, leading to improved electronic conductivity. These attributes are highly beneficial for Li-ion storage capabilities, markedly improving cycle life and rate capability. Moreover, we find that CSRD can be introduced in additional layered oxide materials through improved chemical co-doping, further illustrating its potential to enhance structural and electrochemical stability. These findings open up new avenues for the design of oxide cathodes, offering insights into the effects of CSRD on the crystal and electronic structure of advanced functional materials.

Nanoindentation into a bcc high-entropy HfNbTaTiZr alloy-an atomistic study of the effect of short-range order

The plastic response of the Senkov HfNbTaTiZr high-entropy alloy is explored by means of simulated nanoindentation tests. Both a random alloy and an alloy with chemical short-range order are investigated and compared to the well understood case of an elementary Ta crystal. Strong differences in the dislocation plasticity between the alloys and the elementary Ta crystal are found. The high-entropy alloys show only little relaxation of the indentation dislocation network after indenter retraction and only negligible dislocation emission into the sample interior. Short-range order-besides making the alloy both stiffer and harder-further increases the size of the plastic zone and the dislocation density there. These features are explained by the slow dislocation migration in these alloys. Also, the short-range-ordered alloy features no twinning plasticity in contrast to the random alloy, while elemental Ta exhibits twinning under high stress but detwins considerably under stress relief. The results are in good qualitative agreement with our current knowledge of plasticity in high-entropy alloys.

Multifunctional High Entropy Alloys Enabled by Severe Lattice Distortion

Since 2004, the design of high entropy alloys (HEAs) has generated significant interest within the materials science community due to their exceptional structural and functional properties. By incorporating multiple principal elements into a common lattice, it is possible to create a single-phase crystal with a highly distorted lattice. This unique feature enables HEAs to offer a promising combination of mechanical and physical properties that are not typically observed in conventional alloys. In this article, an extensive overview of multifunctional HEAs that exhibit severe lattice distortion is provided, covering the theoretical models that are developed to understand lattice distortion, the experimental and computational methods employ to characterize lattice distortion, and most importantly, the impact of severe lattice distortion on the mechanical, physical and electrochemical properties of HEAs. Through this review, it is hoped to stimulate further research into the study of distorted lattices in crystalline solids.

Two Birds with One Stone: Contemporaneously Enhancing OER Catalytic Activity and Stability for Dual-Phase Medium-Entropy Metal Sulfides

Transition metal-based sulfides exhibit remarkable potential as electrocatalysts for oxygen evolution reaction (OER) due to the unique intrinsic structure and physicochemical characteristics. Nevertheless, currently available sulfide catalysts based on transition metals face a bottleneck in large-scale commercial applications owing to their unsatisfactory stability. Here, the first fabrication of (FeCoNiMn2 )S2 dual-phase medium-entropy metal sulfide (dp-MEMS) is successfully achieved, which demonstrated the expected optimization of stability in the OER process. Benefiting from the "cell wall" -like structure and the synergistic effect in medium-entropy systems, (FeCoNiMn2 )S2 dp-MEMS delivers an exceptionally low overpotential of 169 and 232 mV at current densities of 10 and 100 mA cm-2 , respectively. The enhancement mechanism of catalytic activity and stability is further validated by density functional theory (DFT) calculations. Additionally, the rechargeable Zn-air batteries integrated with FeCoNiMn2 )S2 dp-MEMS exhibit remarkable performance outperforming the commercial catalyst (Pt/C+RuO2 ). This work demonstrates that the dual-phase medium-entropy metal sulfide-based catalysts have the potential to provide a greater application value for OER and related energy conversion systems.

Computational understanding of the coalescence of metallic nanoparticles: a mini review

Metallic nanoparticles exhibit extraordinary properties that differ from those of bulk materials due to their large surface area to volume ratios. Coalescence of metallic nanoparticles has a huge impact on their properties. Remarkable progress has been made by using computational methods for understanding nanoparticle coalescence. This work aims to provide a mini review on the state-of-the-art modelling and simulation of nanoparticle coalescence. First, we will discuss the outstanding performances and coalescence behaviors of metallic nanoparticles, and list some challenges in the coalescence of metallic nanoparticles. Next, we will introduce the applications of molecular dynamics and the Monte Carlo method in nanoparticle coalescence. Furthermore, we will discuss the coalescence kinetics and mechanisms of metal nanoparticles with the same element and different elements, alloy nanoparticles and metal oxide nanoparticles. Finally, we will present our perspective and conclusion.

Phase Engineering of Nanostructural Metallic Materials: Classification, Structures, and Applications

Metallic materials are usually composed of single phase or multiple phases, which refers to homogeneous regions with distinct types of the atom arrangement. The recent studies on nanostructured metallic materials provide a variety of promising approaches to engineer the phases at the nanoscale. Tailoring phase size, phase distribution, and introducing new structures via phase transformation contribute to the precise modification in deformation behaviors and electronic structures of nanostructural metallic materials. Therefore, phase engineering of nanostructured metallic materials is expected to pave an innovative way to develop materials with advanced mechanical and functional properties. In this review, we present a comprehensive overview of the engineering of heterogeneous nanophases and the fundamental understanding of nanophase formation for nanostructured metallic materials, including supra-nano-dual-phase materials, nanoprecipitation- and nanotwin-strengthened materials. We first review the thermodynamics and kinetics principles for the formation of the supra-nano-dual-phase structure, followed by a discussion on the deformation mechanism for structural metallic materials as well as the optimization in the electronic structure for electrocatalysis. Then, we demonstrate the origin, classification, and mechanical and functional properties of the metallic materials with the structural characteristics of dense nanoprecipitations or nanotwins. Finally, we summarize some potential research challenges in this field and provide a short perspective on the scientific implications of phase engineering for the design of next-generation advanced metallic materials.

Stabilizing 3D-printed metal alloys

A design strategy overcomes the strength-ductility trade-off in alloy manufacturing.

Simultaneous enhancement of strength and ductility via microband formation and nanotwinning in an L12-strengthened alloy

Metallic alloys with high strength and large ductility are required for extreme structural applications. However, the achievement of ultrahigh strength often results in a substantially decreased ductility. Here, we report a strategy to achieve the strength-ductility synergy by tailoring the alloy composition to control the local stacking fault energy (SFE) of the face-centered-cubic (fcc) matrix in an L12-strengthened superlattice alloy. As a proof of concept, based on the thermodynamic calculations, we developed a non-equiatomic CoCrNi2(Al0.2Nb0.2) alloy using phase separation to create a near-equiatomic low SFE disordered CoCrNi medium-entropy alloy matrix with in situ formed high-content coherent Ni3(Al, Nb)-type ordered nanoprecipitates (∼ 12 nm). The alloy achieves a high tensile strength up to 1.6 GPa and a uniform ductility of 33%. The low SFE of the fcc matrix promotes the formation of nanotwins and parallel microbands during plastic deformation which could remarkably enhance the strain hardening capacity. This work provides a strategy for developing ultrahigh-strength alloys with large uniform ductility.

Negative mixing enthalpy solid solutions deliver high strength and ductility

Body-centred cubic refractory multi-principal element alloys (MPEAs), with several refractory metal elements as constituents and featuring a yield strength greater than one gigapascal, are promising materials to meet the demands of aggressive structural applications1-6. Their low-to-no tensile ductility at room temperature, however, limits their processability and scaled-up application7-10. Here we present a HfNbTiVAl10 alloy that shows remarkable tensile ductility (roughly 20%) and ultrahigh yield strength (roughly 1,390 megapascals). Notably, these are among the best synergies compared with other related alloys. Such superb synergies derive from the addition of aluminium to the HfNbTiV alloy, resulting in a negative mixing enthalpy solid solution, which promotes strength and favours the formation of hierarchical chemical fluctuations (HCFs). The HCFs span many length scales, ranging from submicrometre to atomic scale, and create a high density of diffusive boundaries that act as effective barriers for dislocation motion. Consequently, versatile dislocation configurations are sequentially stimulated, enabling the alloy to accommodate plastic deformation while fostering substantial interactions that give rise to two unusual strain-hardening rate upturns. Thus, plastic instability is significantly delayed, which expands the plastic regime as ultralarge tensile ductility. This study provides valuable insights into achieving a synergistic combination of ultrahigh strength and large tensile ductility in MPEAs.

Three-dimensional atomic structure and local chemical order of medium- and high-entropy nanoalloys

Medium- and high-entropy alloys (M/HEAs) mix several principal elements with near-equiatomic composition and represent a model-shift strategy for designing previously unknown materials in metallurgy1-8, catalysis9-14 and other fields15-18. One of the core hypotheses of M/HEAs is lattice distortion5,19,20, which has been investigated by different numerical and experimental techniques21-26. However, determining the three-dimensional (3D) lattice distortion in M/HEAs remains a challenge. Moreover, the presumed random elemental mixing in M/HEAs has been questioned by X-ray and neutron studies27, atomistic simulations28-30, energy dispersive spectroscopy31,32 and electron diffraction33,34, which suggest the existence of local chemical order in M/HEAs. However, direct experimental observation of the 3D local chemical order has been difficult because energy dispersive spectroscopy integrates the composition of atomic columns along the zone axes7,32,34 and diffuse electron reflections may originate from planar defects instead of local chemical order35. Here we determine the 3D atomic positions of M/HEA nanoparticles using atomic electron tomography36 and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order (CSRO). We find that the high-entropy alloys have larger local lattice distortion and more heterogeneous strain than the medium-entropy alloys and that strain is correlated to CSRO. We also observe CSRO-mediated twinning in the medium-entropy alloys, that is, twinning occurs in energetically unfavoured CSRO regions but not in energetically favoured CSRO ones, which represents, to our knowledge, the first experimental observation of correlating local chemical order with structural defects in any material. We expect that this work will not only expand our fundamental understanding of this important class of materials but also provide the foundation for tailoring M/HEA properties through engineering lattice distortion and local chemical order.

Sub-Ångstrom-scale structural variations in high-entropy oxides

High-entropy oxides (HEOs) are a special class of materials that utilize the concept of high-entropy alloys (HEAs) with five or more elements randomly distributing at a single sublattice in near-equiatomic proportions. HEOs have been attracting increasing attention owing to their many outstanding physical and chemical properties. However, unlike HEAs, for which local chemical compositions, order/disorder behaviors, and property-structure relationships have been comprehensively investigated, detailed information on the atomic-scale chemical and structural features and their correlations with functionalities in HEOs so far is still not sufficient. Herein, we select four typical HEOs with pyrochlore, spinel, perovskite and rock-salt type structures, and directly observe and quantify sub-Ångstrom-scale structure variations in different manners by means of advanced aberration-corrected scanning transmission electron microscopy techniques. Visualization and quantification of local structural variations and lattice distortions in the current work may show a valuable example for future investigations on local fluctuating structures and their relationships with properties in more systems of HEOs.

Room-temperature super-elongation in high-entropy alloy nanopillars

Nanoscale small-volume metallic materials typically exhibit high strengths but often suffer from a lack of tensile ductility due to undesirable premature failure. Here, we report unusual room-temperature uniform elongation up to ~110% at a high flow stress of 0.6-1.0 GPa in single-crystalline <110>-oriented CoCrFeNi high-entropy alloy nanopillars with well-defined geometries. By combining high-resolution microscopy and large-scale atomistic simulations, we reveal that this ultrahigh uniform tensile ductility is attributed to spatial and synergistic coordination of deformation twinning and dislocation slip, which effectively promote deformation delocalization and delay necking failure. These joint and/or sequential activations of the underlying displacive deformation mechanisms originate from chemical compositional heterogeneities at the atomic level and resulting wide variations in generalized stacking fault energy and associated dislocation activities. Our work provides mechanistic insights into superplastic deformations of multiple-principal element alloys at the nanoscale and opens routes for designing nanodevices with high mechanical reliability.

Ideal plasticity and shape memory of nanolamellar high-entropy alloys

Understanding the relationship among elemental compositions, nanolamellar microstructures, and mechanical properties enables the rational design of high-entropy alloys (HEAs). Here, we construct nanolamellar AlxCoCuFeNi HEAs with alternating high- and low-Al concentration layers and explore their mechanical properties using a combination of molecular dynamic simulation and density functional theory calculation. Our results show that the HEAs with nanolamellar structures exhibit ideal plastic behavior during uniaxial tensile loading, a feature not observed in homogeneous HEAs. This remarkable ideal plasticity is attributed to the unique deformation mechanisms of phase transformation coupled with dislocation nucleation and propagation in the high-Al concentration layers and the confinement and slip-blocking effect of the low-Al concentration layers. Unexpectedly, this ideal plasticity is fully reversible upon unloading, leading to a remarkable shape memory effect. Our work highlights the importance of nanolamellar structures in controlling the mechanical and functional properties of HEAs and presents a fascinating route for the design of HEAs for both functional and structural applications.

An A2 B2 O7 -Type High-Entropy Oxide for Efficient Photoelectrochemical Photodetector with Excellent Long-Term Stability

Optoelectronics with excellent long-term stability is meaningful for practical applications. Herein, for the first time, an A2 B2 O7 type high-entropy oxide of (La0.2 Ce0.2 Nd0.2 Gd0.2 Bi0.2 )2 Ti2 O7 (ATO) is synthesized and applied for photoelectrochemical photodetection. The lattice distortion, highly dispersed metal composition, and exposed active sites of ATO are beneficial for the fast separation and transmission of photogenerated electron/hole pairs, endowing ATO-based devices with good photodetection performance. Both the density functional theory calculations and the nondegenerate transient absorption spectroscopy demonstrate the good optoelectronic properties of ATO. The systematic experimental studies reveal the tunable photodetection capability of ATO-based photodetector (PD) in the visible region. A photocurrent of 772.00 nA cm-2 and a responsivity of 4.02 µA W-1 can be achieved as the PD in 1.0 m KOH with the bias potential of 0.6 V. Importantly, the robust and reproducible ON/OFF signals of the PD can be verified and there is only ≈5.00% attenuation in photocurrent even after 6 months, revealing the great potential of high- entropy oxides for practical applications.

Sonication and heat-mediated synthesis, characterization and larvicidal activity of sericin-based silver nanoparticles against dengue vector (Aedes aegypti)

Fabrication, characterization and evaluation of the larvicidal potential of novel silk protein (sericin)-based silver nanoparticles (Se-AgNPs) were the prime motives of the designed study. Furthermore, investigation of the sericin as natural reducing or stabilizing agent was another objective behind this study. Se-AgNPs were synthesized using sonication and heat. Fabricated Se-AgNPs were characterized using particle size analyzer, UV spectrophotometry, FTIR and SEM which confirmed the fabrication of the Se-AgNPs. Size of sonication-mediated Se-AgNPs was smaller (7.49 nm) than heat-assisted Se-AgNPs (53.6 nm). Being smallest in size, sonication-assisted Se-AgNPs revealed the significantly highest (F4,10  = 39.20, p = .00) larvicidal activity against fourth instar lab and field larvae (F4,10  = 1864, p = .00) of dengue vector (Aedes aegypti) followed by heat-assisted Se-AgNPs and positive control (temephos). Non-significant larvicidal activity was showed by silver (without sericin) which made the temperature stability of silver, debatable. Furthermore, findings of biochemical assays (glutathione-S transferase, esterase, and acetylcholinesterase) showed the levels of resistance in field strain larvae. Aforementioned findings of the study suggests the sonication as the best method for synthesis of Se-AgNPs while the larvicidal activity is inversely proportional to the size of Se-AgNPs, i.e., smallest the size, highest the larvicidal activity. Conclusively, status of the sericin as a natural reducing/stabilizing agent has been endorsed by the findings of this study. RESEARCH HIGHLIGHTS: Incorporation of biocompatible and inexpensive sericin as a capping/reducing agent for synthesis of Se-AgNPs. A novel sonication method was used for the fabrication of Se-AgNPs which were thoroughly characterized by particle size analyzer, UV-visible spectrophotometry, SEM and FTIR. Analysis of enzymatic (GSTs, ESTs) levels in field and lab strains of Aedes aegypti larvae for evaluation of insecticides resistance.

Chemical inhomogeneity-induced profuse nanotwinning and phase transformation in AuCu nanowires

Nanosized metals usually exhibit ultrahigh strength but suffer from low homogeneous plasticity. The origin of a strength-ductility trade-off has been well studied for pure metals, but not for random solid solution (RSS) alloys. How RSS alloys accommodate plasticity and whether they can achieve synergy between high strength and superplasticity has remained unresolved. Here, we show that face-centered cubic (FCC) RSS AuCu alloy nanowires (NWs) exhibit superplasticity of ~260% and ultrahigh strength of ~6 GPa, overcoming the trade-off between strength and ductility. These excellent properties originate from profuse hexagonal close-packed (HCP) phase generation (2H and 4H phases), recurrence of reversible FCC-HCP phase transition, and zigzag-like nanotwin generation, which has rarely been reported before. Such a mechanism stems from the inherent chemical inhomogeneity, which leads to widely distributed and overlapping energy barriers for the concurrent activation of multiple plasticity mechanisms. This naturally implies a similar deformation behavior for other highly concentrated solid-solution alloys with multiple principal elements, such as high/medium-entropy alloys. Our findings shed light on the effect of chemical inhomogeneity on the plastic deformation mechanism of solid-solution alloys.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

High-Temperature Mechanical Properties of NbTaHfTiZrV0.5 Refractory High-Entropy Alloys

The NbTaHfTiZrV0.5 is a refractory multi-principal-element alloy with high strength and good ductility at room temperature. It is important for possible high-temperature applications to investigate the deformation mechanism of the NbTaHfTiZrV0.5 alloy at different temperatures using tensile tests. In this investigation, the tensile tests were conducted at room temperature to 1273 K on sheet materials fabricated by cold rolling combined with annealing treatments. At 473 K, the NbTaHfTiZrV0.5 alloy exhibited a high tensile ductility (12%). At a testing temperature range of 673~873 K, the ductility was reduced, but the yield strength remained above 800 MPa, which is rare in most other alloys. The TEM investigations revealed that a dislocation slip controlled the plastic deformation, and the degree of deformation was closely related to the dislocation density. The true stress-strain curves of the alloy under different deformation conditions were obtained by tensile deformation at different deformation temperatures (673~873 K) and strain rates (0.001~0.0005 s-1). Experimental results were utilized to construct the parameters of a constitutive model based on a traditional mathematical model to predict the flow behavior at high temperatures. The excellent high-temperature mechanical properties of the NbTaHfTiZrV0.5 alloy will enable it to be used in several engineering applications.

The Influence of Coherent Oxide Interfaces on the Behaviors of Helium (He) Ion Irradiated ODS W

Tungsten (W), as a promising plasma-facing material for fusion nuclear reactors, exhibits ductility reduction. Introducing high-density coherent nano-dispersoids into the W matrix is a highly efficient strategy to break the tradeoff of the strength-ductility performance. In this work, we performed helium (He) ion irradiation on coherent oxide-dispersoids strengthened (ODS) W to investigate the effect of coherent nanoparticle interfaces on the behavior of He bubbles. The results show that the diameter and density of He bubbles in ODS W are close to that in W at low dose of He ion irradiation. The radiation-induced hardening increment of ODS W, being 25% lower than that of pure W, suggests the involvement of the coherent interface in weakening He ion irradiation-induced hardening and emphasizes the potential of coherent nano-dispersoids in enhancing the radiation resistance of W-based materials.

Exceptional enhancement of mechanical properties in high-entropy alloys via thermodynamically guided local chemical ordering

Understanding the local chemical ordering propensity in random solid solutions, and tailoring its strength, can guide the design and discovery of complex, paradigm-shifting multicomponent alloys. First, we present a simple thermodynamic framework, based solely on binary enthalpies of mixing, to select optimal alloying elements to control the nature and extent of chemical ordering in high-entropy alloys (HEAs). Next, we couple high-resolution electron microscopy, atom probe tomography, hybrid Monte-Carlo, special quasirandom structures, and density functional theory calculations to demonstrate how controlled additions of Al and Ti and subsequent annealing drive chemical ordering in nearly random equiatomic face-centered cubic CoFeNi solid solution. We establish that short-range ordered domains, the precursors of long-range ordered precipitates, inform mechanical properties. Specifically, a progressively increasing local order boosts the tensile yield strengths of the parent CoFeNi alloy by a factor of four while also substantially improving ductility, which breaks the so-called strength-ductility paradox. Finally, we validate the generality of our approach by predicting and demonstrating that controlled additions of Al, which has large negative enthalpies of mixing with the constituent elements of another nearly random body-centered cubic refractory NbTaTi HEA, also introduces chemical ordering and enhances mechanical properties.

Ultra-Small High-Entropy Alloy Nanoparticles: Efficient Nanozyme for Enhancing Tumor Photothermal Therapy

High-entropy alloys nanoparticles (HEANPs) are receiving extensive attention due to their broad compositional tunability and unlimited potential in bioapplication. However, developing new methods to prepare ultra-small high-entropy alloy nanoparticles (US-HEANPs) faces severe challenges owing to their intrinsic thermodynamic instability. Furthermore, there are few reports on studying the effect of HEANPs in tumor therapy. Herein, the fabricated PtPdRuRhIr US-HEANPs act as bifunctional nanoplatforms for the highly efficient treatment of tumors. The US-HEANPs are engineered by the universal metal-ligand cross-linking strategy. This simple and scalable strategy is based on the aldol condensation of organometallics to form the target US-HEANPs. The synthesized US-HEANPs exhibit excellent peroxidase-like (POD-like) activity and can catalyze the endogenous hydrogen peroxide to produce highly toxic hydroxyl radicals. Furthermore, the US-HEANPs possess a high photothermal conversion effect for converting 808 nm near-infrared light into heat energy. In vivo and in vitro experiments demonstrated that under the synergistic effect of POD-like activity and photothermal action, the US-HEANPs can effectively ablate cancer cells and treat tumors. It is believed that this work not only provides a new perspective for the fabrication of HEANPs, but also opens the high-entropy nanozymes research direction and their biomedical application.

Superior zero thermal expansion dual-phase alloy via boron-migration mediated solid-state reaction

Rapid progress in modern technologies demands zero thermal expansion (ZTE) materials with multi-property profiles to withstand harsh service conditions. Thus far, the majority of documented ZTE materials have shortcomings in different aspects that limit their practical utilization. Here, we report on a superior isotropic ZTE alloy with collective properties regarding wide operating temperature windows, high strength-stiffness, and cyclic thermal stability. A boron-migration-mediated solid-state reaction (BMSR) constructs a salient "plum pudding" structure in a dual-phase Er-Fe-B alloy, where the precursor ErFe₁₀ phase reacts with the migrated boron and transforms into the target Er₂Fe₁₄B (pudding) and α-Fe phases (plum). The formation of such microstructure helps to eliminate apparent crystallographic texture, tailor and form isotropic ZTE, and simultaneously enhance the strength and toughness of the alloy. These findings suggest a promising design paradigm for comprehensive performance ZTE alloys.

Ultra-strong tungsten refractory high-entropy alloy via stepwise controllable coherent nanoprecipitations

High-performance refractory alloys with ultrahigh strength and ductility are in demand for a wide range of critical applications, such as plasma-facing components. However, it remains challenging to increase the strength of these alloys without seriously compromising their tensile ductility. Here, we put forward a strategy to "defeat" this trade-off in tungsten refractory high-entropy alloys by stepwise controllable coherent nanoprecipitations (SCCPs). The coherent interfaces of SCCPs facilitate the dislocation transmission and relieve the stress concentrations that can lead to premature crack initiation. As a consequence, our alloy displays an ultrahigh strength of 2.15 GPa with a tensile ductility of 15% at ambient temperature, with a high yield strength of 1.05 GPa at 800 °C. The SCCPs design concept may afford a means to develop a wide range of ultrahigh-strength metallic materials by providing a pathway for alloy design.

Synthesis and structural properties of high-entropy nanoalloys made by physical and chemical routes

The development of synthesis methods with enhanced control over the composition, size and atomic structure of High Entropy Nano-Alloys (HENA) could give rise to a new repertoire of nanomaterials with unprecedented functionalities, notably for mechanical, catalytic or hydrogen storage applications. Here, we have developed two original synthesis methods, one by a chemical route and the other by a physical one, to fabricate HENA with a size between 3 and 10 nm and a face centered cubic structure containing three (CoNiPt), four (CoNiPtCu and CoNiPtAu) or five (CoNiPtAuCu) metals close to the equiatomic composition. The key point in the proposed chemical synthesis method is to compensate the difference in reactivity of the different metal precursors by increasing the synthesis temperature using high boiling solvents. Physical syntheses were performed by pulsed laser ablation using a precise alternating deposition of the individual metals on a heated amorphous carbon substrate. Finally, we have exploited aberration-corrected transmission electron microscopy to explore the nanophase diagram of these nanostructures and reveal intrinsic thermodynamic properties of those complex nanosystems. In particular, we have shown (i) that the complete mixing of all elements can only occur close to the equiatomic composition and (ii) how the Ostwald ripening during HENA synthesis can induce size-dependent deviations from the equiatomic composition leading to the formation of large core-shell nanoparticles.

Plasticity Improvement in a Co-Rich Co40Fe25Cr20Ni15 High-Entropy Alloy via Al Alloying

The mechanical properties of high-entropy alloys (HEAs) can be regulated by altering the stacking fault energy (SFE) through compositional modulation. The Co-rich HEAs, exhibiting deformation twinning and even strain-induced martensitic transformation at room temperature, suffer from insufficient ductility at high strength. In this work, we developed Co-rich (Co₄₀Fe₂₅Cr₂₀Ni₁₅)_100-xAl_x (x = 0 and 5 at.%) HEAs and investigated their tensile behaviors at room temperature. The addition of Al resulted in a massive improvement in the strength-ductility product, even at similar grain sizes, and also altered the fracture mode from quasi-cleavage to ductile dimple fracture. Interestingly, both alloys were deformed by mechanical twinning, which was also verified by molecular dynamics (MD) simulations. The MD simulations revealed the SFE increased upon Al addition; however, the slip energy barrier was reduced, which favored the mobility of dislocations and twinning propensity to prolong strain hardening. The present findings provide further insights into the regulation of mechanical properties of HEAs by Al-alloying.

Nanoprecipitates to Enhance Radiation Tolerance in High-Entropy Alloys

The growth of advanced energy technologies for power generation is enabled by the design, development, and integration of structural materials that can withstand extreme environments, such as high temperatures, radiation damage, and corrosion. High-entropy alloys (HEAs) are a class of structural materials in which suitable chemical elements in four or more numbers are mixed to typically produce single-phase concentrated solid solution alloys (CSAs). Many of these alloys exhibit good radiation tolerance like limited void swelling and hardening up to relatively medium radiation doses (tens of displacements per atom (dpa)); however, at higher radiation damage levels (>50 dpa), some HEAs suffer from considerable void swelling limiting their near-term acceptance for advanced nuclear reactor concepts. In this study, we developed a HEA containing a high density of Cu-rich nanoprecipitates distributed in the HEA matrix. The Cu-added HEA, NiCoFeCrCu_0.12, shows excellent void swelling resistance and negligible radiation-induced hardening upon irradiation up to high radiation doses (i.e., higher than 100 dpa). The void swelling resistance of the alloy is measured to be significantly better than NiCoFeCr CSA and austenitic stainless steels. Density functional theory simulations predict lower vacancy and interstitial formation energies at the coherent interfaces between Cu-rich nanoprecipitates and the HEA matrix. The alloy maintained a high sink strength achieved via nanoprecipitates and the coherent interface with the matrix at a high radiation dose (∼50 dpa). From our experiments and simulations, the effective recombination of radiation-produced vacancies and interstitials at the coherent interfaces of the nanoprecipitates is suggested to be the critical mechanism responsible for the radiation tolerance of the alloy. The materials design strategy based on incorporating a high density of interfaces can be applied to high-entropy alloy systems to improve their radiation tolerance.