Oxygen interstitial solutes have traditionally been thought to occupy only octahedral interstices in body-centered cubic (bcc) metals. However, the competition between tetrahedral and octahedral interstitial sites for oxygen solutes in multi-principal element alloys has become a topic of debate. The driving force and atomistic mechanism behind this observed preference switch remain unclear. In this study, we systematically investigate the competition between tetrahedral and octahedral sites for oxygen, nitrogen, and carbon solute atoms in bcc NbTiZr alloys using density functional theory calculations. At dilute concentrations, interstitial solutes exhibit a strong preference for octahedral sites, with 100 % of solutes initially placed in tetrahedral sites migrating to nearby octahedral sites after structural relaxation. Notably, a transition from octahedral site to tetrahedral site occupancy is observed under specific conditions, including lattice expansion, high interstitial solute concentrations, or significant spatial heterogeneity (reflecting locally aggregated oxygen interstitials), provided no phase transformation occurs. This transition is driven by a crossover in elastic strain energy between the two competing configurations of octahedral and tetrahedral interstices. Our findings provide mechanistic insights into the behavior of small interstitial solutes and their solid solution strengthening effects in bcc multi-principal element alloys, offering valuable guidance for alloy design. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Overcoming the strength-ductility trade-off in face-centered cubic high-entropy alloys requires strengthening while regulating deformation instability. Here, we engineer multifunctional B2 grains to control transformation kinetics and strain accommodation in a nanoprecipitate-strengthened FeCoNiAlTaB high-entropy alloy. The hierarchical microstructure, comprising a metastable face-centered cubic matrix, coherent nanoscale L12 precipitates, and micrometer-scale B2 grains, enables sustained work hardening through progressive transformation-induced plasticity. Unlike conventional brittle intermetallics, the B2 grains act simultaneously as metastability regulators, martensite nucleation catalysts, grain refiners, and plastically deformable stress relievers. Together with L12-mediated strengthening and spatial confinement of transformation, this multifunctionality suppresses abrupt transformation and delays strain localization. Consequently, the alloy achieves ∼1,450 MPa tensile strength and ∼31% uniform elongation, representing a rare simultaneous increase in strength and ductility after aging. These results establish multifunctional second-phase engineering as a route to sustained hardening and damage tolerance in structural alloys.

Body-centered cubic (bcc) alloys can achieve gigapascal-level yield strengths but typically are limited in tensile ductility (<20%), contrasting sharply with elemental metals (the largest elongation of ~50%). Multi-principal-element alloys offer vast compositional space to reach synergistic strength-ductility combinations. However, combinatorial trial-and-error exploration is prohibitively costly, while machine learning (ML) approaches are hindered by data scarcity. Here, we develop an ML-guided framework integrating active learning with physics-informed Bayesian optimization to rapidly converge on optimal compositions. The resulting Ti36V14Nb22Hf22Zr1Al5 alloy achieves a yield strength of 953 MPa and a large tensile ductility of 42%. The high strength arises from the substantial lattice distortion, as well as the ~1-nm-sized local chemical fluctuations (LCFs) inherent to the highly concentrated bcc solid solution. The ubiquitous LCFs also substantially promote dislocation multiplication and strain hardening, enabling a large tensile ductility. Our approach demonstrates ML's efficacy in accelerating the finding of high-performance alloys.

Precipitation hardening is a well-known strategy that can raise the yield strength of alloys to well over 1 GPa, including at 77 K, but is less potent in offering strain hardening than twinning/transformation-induced-plasticity (TWIP/TRIP) mechanisms, which have been essential for the high ductility and fracture toughness of established cryogenic alloys. Here we demonstrate an innovative strategy to tailor the coherent nanoprecipitates by purposely designing negative-curvature interfaces (NCIs). This morphological control uses the geometric curvature and curvature-gradient effects to generate additional local stress, high elastic energy density, and substantial strain gradients to make NCIs prolific sources of dislocation nucleation. The proliferation of partial dislocations builds up ultra-dense hierarchical stacking-faults dynamically all over the deforming volume, substantially enhancing strain-hardening and toughening. The resulting NiCoCrAlTa alloy exhibits excellent cryogenic mechanical properties, achieving a high yield strength of 1.26 GPa, a product (~90 MPa%) of ultimate tensile strength (~1.80 GPa) with tensile ductility (~50%) and a fracture toughness of 213 MPa·m1/2 at 77 K-representing a record-high combination among all reported alloys to date. Our interface design strategy may be applicable to all precipitation-hardened alloys, transforming the precipitates from merely passive strengtheners to active and tunable agents regulating the plastic flow.

The recently proposed term "heterostructured (HS) materials" serves as an umbrella classification encompassing a wide range of materials with significant potential for enhanced mechanical properties. Most HS materials exhibit back-stress strengthening, as is typical for all plastically non-homogeneous materials. To better embody the distinctiveness of materials crafted via innovative heterostructuring, here we introduce the concept of "structural gradient hardening" (SGH), which captures an essential feature of HS materials and complements traditional strengthening mechanisms. SGH refers to the extra strengthening that arises from a characteristic gradient structure introduced by heterostructuring, beyond what is predicted by the rule of mixtures. This distinction is useful, as the overall back stress can in fact be partitioned into Type I and Type II components, with the latter specifically quantifying the additional hardening originating from the structural and strain gradients established by heterostructuring, as articulated in this Viewpoint article.

Nanocrystalline (NC) metals possess high strength due to its extremely small grain size, but the strength-plasticity trade-off, poor thermal stability, and limitation to a few micrometers in size have seriously hampered their widespread application for a long time. Here, we propose a universal and facile strategy to solve these problems all at once, by exploiting the synergistic aspect of rapid electrical-current-activated sintering (RECAS) and multi-component NC alloy. We demonstrate RECAS as an efficient way to achieve dense and robust claddings versatile in dimensions (i.e., >= 1 mm in thickness), also with uniform NC grain sizes. The NC CoCrNi medium-entropy alloy cladding is used to demonstrate the simultaneous realization of excellent strength-plasticity combination, and unprecedented high thermal stability of NC grain size up to similar to 0.84Tm (Tm, melting point), and the robust performance in terms of resistance to wear, corrosion and cavitation erosion. These advances open an avenue to a much-expanded repertoire of available parts made of NC metals/alloys (including their size, shape and composition), as well as an increased flexibility with regard to property combinations that extend application possibilities.

The pursuit of strong yet ductile alloys has been ongoing for centuries. However, for all alloys developed thus far, including recent high-entropy alloys, those possessing good tensile ductility rarely approach 2-GPa yield strength at room temperature. The few that do are mostly ultra-strong steels1-3; however, their stress-strain curves exhibit plateaus and serrations because their tensile flow suffers from plastic instability (such as Lüders strains)1-4, and the elongation is pseudo-uniform at best. Here we report that a group of carefully engineered multi-principal-element alloys, with a composition of Fe35Ni29Co21Al12Ta3 designed by means of domain knowledge-informed machine learning, can be processed to reach an unprecedented range of simultaneously high strength and ductility. An example of this synergy delivers 1.8-GPa yield strength combined with 25% truly uniform elongation. We achieved strengthening by pushing microstructural heterogeneities to the extreme through unusually large volume fractions of not only coherent L12 nanoprecipitates but also incoherent B2 microparticles. The latter, being multicomponent with a reduced chemical ordering energy, is a deformable phase that accumulates dislocations inside to help sustain a high strain hardening rate that prolongs uniform elongation.

Spontaneous structural relaxation is intrinsic to glassy materials due to their metastable nature. For phase-change materials (PCMs), the resultant temporal change in electrical resistance seriously hamper in-memory computing (IMC) applications. Here, we report an ab-initio-calculation-informed design of amorphous PCM composed of robust "molecule-like" motifs with minimal Peierls distortion, depriving the amorphous alloy of structural ingredients that would gradually evolve upon aging to entail resistance drift. We demonstrate amorphous CrTe3 thin films that display practically no resistance drift at any working temperature from -200 to 165 degree C. We achieve multilevel programming of CrTe3 through both step-wise crystallization and step-wise amorphization using a hybrid opto-electronic device at various temperatures. Moreover, the application potential of CrTe3 in neuromorphic computing is testified by its incorporation in a vehicle with automatic path-tracking function. Our work opens a new avenue to achieving IMC-requisite properties via judicious design of the composition and atomic-level structure of disordered PCM alloys.

High entropy carbides (HECs) ceramics are promising candidates for high-temperature ablation-resistance materials. However, the limited thermal conductivity and mechanical properties still impede its capability to survive in extreme ablation environment. Here, we design the high entropy carbide Hf0.5Zr0.3Ti0.1Ta0.1C, denoted as HZTTC, integrated with refractory tungsten mesh. This composite remains intact subjected to ablation at 2500 degrees C. Its linear ablation rate (LAR) and mass ablation rate (MAR) achieve decent values of -1.75 mu ms(-1) and -0.149 mgs(-1)cm(-2). This decent ablation performance is characteristic of various ablation resistant oxides with unique morphologies, such as lamellar, flocculent, needlelike, and rod-shaped oxides. Surprisingly, the composite still reveals attractive ablation properties with the LAR of -0.75 mu ms(-1) and the MAR of -0.072 mgs(-1)cm(-2), even when the ablation temperature goes up to 2700 degrees C for 600 s. Moreover, the ceramic-metal composite achieves a high thermal conductivity of 25.72 Wm(-1)K-1, demonstrating a 16.7 % enhancement to that of the pure HZTTC ceramic. Moreover, this composite also reveals a high hardness of 22.21 GPa and a fracture toughness of 5.64 MPam(1)(/)(2). This decent ablation performance, high thermal conductivity and peculiar mechanical properties enable this composite to be a potential alternative for protecting hypersonic aircraft severing in extreme environments.

An oxide-dispersion-strengthened (ODS) Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging. The intentionally promoted heterogeneous microstructure consists of coarse-grained “core” regions enclosed by mutually connected fine-grained “shell” zones, facilitated by unevenly distributed oxide particles. The sample sintered and then forged at 1150 ℃ exhibited a yield strength of 598 MPa, a tensile strength of 734 MPa, and a fracture elongation of 25.1%. Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts. During tensile deformation, a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dislocations was observed near the interfaces of matrix/oxide particles, both contributing to heterogeneous deformation-induced strengthening. This elevates the work hardening rate and consequently the tensile elongation. Quantitative analysis indicates that the dislocation build-up during forging makes the dominant contribution to the high yield strength of Ox-1150. The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy.

Designing alloys capable of withstanding irradiation is a crucial aspect of developing materials for nuclear reactors and aerospace applications. Local chemical order (LCO) has recently been recognized as a new microstructural parameter to leverage, and its effect on the mechanical properties of body-centered cubic (BCC) multi-principal element alloys (MPEAs) has attracted much attention. However, the impact of LCO on the dynamic evolution of irradiation-induced defects in BCC MPEAs remains much less explored. In this study, we engineered varying degrees of LCO and local lattice distortion in NbZrTi BCC MPEAs by alloying them with different concentrations of interstitial oxygen solutes, and analyzed their effects on the evolution of radiation-induced defects during He irradiation at 673 K to 873 K, with a fluence of 5 x 1016 ions/cm2 and a peak dose of approximately 1 DPA. Using first-principles calculations and atomic-scale analysis of microstructures and chemical elements, we discovered that interstitial oxygen atoms enhance LCO and increase local lattice distortion. These heterogeneities increase the formation energy, and localize the diffusion, of vacancies, hence effectively reducing the transport of aggregating helium that causes bubble swelling. The initiation and growth of dislocation loops and precipitates are depressed as well. The manipulation of irradiation defects in BCC MPEAs, through orchestrating interstitial oxygen solutes and the LCO they provoke, adds a practical strategy for designing advanced alloys for nuclear applications. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Shear bands (SBs) play a critical role in determining the mechanical behavior of metallic glasses (MGs). However, the rapid dynamics and highly localized nature of SB propagation present significant challenges for direct observation of their atomistic mechanisms using experimental techniques. In this study, we employ hybrid molecular dynamics/Monte Carlo simulations to investigate the atomic-scale mechanisms of SB propagation in Mg65Cu25Y10 MGs, prepared using cooling rates as slow as 104 K s-1-comparable to experimental casting conditions and significantly slower than the 1010 K s-1 rates previously employed in atomistic simulations. Our results reveal a qualitative shift in SB propagation mechanisms as the structural state evolves with decreasing cooling rates. In hyperquenched MGs, SB propagation occurs intermittently, characterized by a "stop-and-go" motion driven by sequential activation and coalescence of multiple shear transformation zones (STZs) separated by vortex-like fields. In contrast, slowly cooled MGs exhibit continuous and rapid SB propagation, mediated by localized shear softening and the formation of large vortex fields, indicative of a more collective structural response. This transition arises from significant differences in the number density and spatial distribution of activated STZs across different structural states. These findings provide insights into the microscopic dynamics of SB initiation and propagation in MGs, highlighting how the structural state can be strategically tuned to control SB behavior. This opens up different opportunities for optimizing the mechanical performance of MGs for targeted engineering applications.

The chemical short-range order (CSRO) in multi-principal element alloys (MPEAs) critically influences their microstructural and various properties. Conventional density functional theory (DFT)-based Monte Carlo (MC) simulations, though accurate, are computationally expensive and limited to small-scale systems. This study introduces a novel local-lattice-distortion (LLD)-based MC framework as a computationally efficient alternative for predicting CSRO. By replacing energy-based acceptance criteria with LLD reduction as the metric for atomic swaps, our method achieves computational speeds over two orders of magnitude faster than DFT-based methods while maintaining accuracy. Validated on six representative face-centered cubic and body-centered cubic MPEAs, the framework reveals a strong correlation between LLD and CSRO. Its scalability enables applications in large-scale simulations and high-throughput studies, providing actionable insights into the LLD-CSRO relationship. This methodology offers a transformative tool for advancing the design and optimization of MPEAs with tailored properties.

Refractory multi-principal element alloys (RMPEAs) have garnered attention for their potential in high-temperature applications. Additive manufacturing (AM) provides opportunities to tailor RMPEAs’ microstructures to enhance these properties. However, controlling defects and addressing the challenges posed by the complex thermal history during the AM process are crucial for optimizing RMPEAs’ performance. This study aims to fabricate a high-quality oxygen-doped NbTiZr alloys using laser powder bed fusion and investigate their microstructure and mechanical properties. Our analysis reveals refined grain sizes and a periodic combination of fine near-equiaxed and columnar grain morphologies in the AM-fabricated alloy. Its substructure is characterized by the coexistence of loosely defined cellular dislocation networks and elemental segregation. Compared to its cast counterpart, the additively manufactured alloy exhibits a combination of high yield strength, excellent tensile ductility, and enhanced work hardening. These attributes make the AM-fabricated oxygen-doped NbTiZr alloy a promising candidate for applications required balanced mechanical properties. Understanding the specific effects of different crystal structures and deformation mechanisms is essential for optimizing AM processes to tailor the microstructure and achieve the desired mechanical performance in various engineering applications.

Nanoparticles or precipitates are long used to block dislocations to strengthen metals. However, this strengthening mechanism unavoidably adds stress concentrations at the obstacles, instigating crack initiation that hampers ductility. Here, we demonstrate a strategy that replaces the traditional crystalline dispersions with dense amorphous nanoparticles, which is made possible via laser powder bed fusion. Porosity-free copper-based nanocomposites are demonstrated as a prototype, consisting of densely and uniformly distributed amorphous boron-carbide nanoparticles (~47 nm in average diameter, up to 12% volume fraction) via an in situ nanofragmentation and melt-quench process. The amorphous nanoparticles act as dislocation sinks, thereby alleviating local stress concentration. They also self-harden along with tensile deformation, promoting strain hardening and therefore homogeneous plastic flow. The as-built composite achieves a tensile strength of more than one gigapascal and a total elongation of approximately 10%, more than twice that of its crystalline dispersion counterpart. Defect accumulation is also suppressed upon cyclic deformation of the as-built bulk nanocomposites, delivering a fatigue strength limit (at > 107 cycles) of more than 70% of the tensile strength. Our results demonstrate an effective strategy for additive manufacturing of metallic materials with superior properties.

The classical Debye model successfully predicts phononic contribution to the specific heat of solids in the continuum limit. However, as the phonon wavenumber increases, their vibrational density of states gradually deviates from the Debye prediction and eventually manifests as Van Hove singularities for crystals and a boson peak for glasses. So far, there is still much controversy over whether these two non-Debye anomalies are equivalent or not. Here we propose a unified model and demonstrate that it describes the vibrational density of states in both crystals and glasses. We achieve this by treating the vibrational excitation of solids as the elastic phonons resonating with local modes. Our modelling enables the construction of a phase diagram of non-Debye phonon anomalies. We clarify that the Van Hove singularity and boson peak can evolve as two variants of the same entity when the dispersion displays continuous softening; otherwise, they emerge separately due to resonance-induced extra acoustic softening, further proving by their coexistence. The model is supported by a comparison with experimental heat capacity data over a wide range of real solids, including 143 crystalline and glassy substances. These findings provide a unified picture of the Van Hove singularity and boson peak, and deepen our fundamental understanding of the continuum elasticity of real solids.

Multi-principal element alloys (MPEAs), also known as high-entropy alloys, are highly concentrated solid solutions more complex than the initially assumed ideal solid solutions. Using a combination of theoretical predictions and numerical simulations, this study quantitatively evaluates the degree of local compositional fluctuation in MPEAs and maps out how it depends on the number of principal elements and the constituent atomic concentrations. Shannon entropy is introduced as a metric to assess the compositional complexity, which is found to be maximized at the equiatomic composition, emphasizing the impact of balanced elemental proportions. We advocate the Shannon entropy, being more directly related to MPEA properties, as an indicator better than the configurational entropy to carry/capture the "high entropy" concept than configurational entropy.

Metal injection moulding (MIM) has been widely used in manufacturing components of iron-base alloys, stainless steels, and copper and titanium alloys, due to its advantages in fabricating small parts in high quantities and of complex shape. However, the application of MIM for aluminum alloys is severely limited by their insufficient densification and mechanical properties, caused by defects left after sintering due to the oxide layer on the surface of aluminum powders. Here, we introduce an oxalic acid catalytic degreasing process, which effectively overcomes the adverse effects of the oxide layer and enables the fabrication of highly dense MIM 6061 aluminum alloys (with a density of 99.5 % of theoretical). Besides, the SiO2 formed during the degreasing process serves as a reactive precursor, transforming the otherwise traditionally detrimental oxide layer into a beneficial reactant that facilitates the formation of a nano-MgAl2O4 quasi-network heterostructure. Remarkably, the heat-treated MIM 6061 aluminum alloy exhibits an excellent strength-ductility synergy of a yield strength 317.4 +/- 9.2 MPa, an ultimate tensile strength 366.8 +/- 8.3 MPa and an elongation 11.6 +/- 0.2 %, comparable to those of heattreated wrought and additively manufactured 6061 aluminum alloys. High density together with the formation of the heterogeneous structure offers high performance and opens up new opportunities for wide industrial application of MIM aluminum alloys.

Achieving a robust strength-ductility balance across a wide temperature range remains a major challenge for refractory high-entropy alloys (RHEAs). In this study, we design a cold-workable NbTaTiHf-based RHEA with a thermally stable heterogeneous grain structure created through thermomechanical processing. This tailored microstructure enables exceptional mechanical performance, from cryogenic (77 K) to elevated temperatures (973 K), achieving tensile strengths exceeding 1.8 GPa at 77 K and maintaining over 900 MPa at 973 K. The primary mechanism responsible for this performance is a highly refined heterogeneous microstructure, which is rendered thermally stable even after extended annealing at high temperatures by the concentrated refractory elements that entail sluggish kinetics. As such, the hetero-deformation-induced (HDI) strengthening mechanisms can be maintained effectively even in high-temperature regimes. Our work offers a practical design approach for next-generation RHEAs with superior mechanical properties across a wide range of temperatures.

Achieving high recoverability is essential to maintaining the structural integrity for Ni-based superalloy single crystals. However, the recovery and recrystallization mechanisms in Ni-based superalloys after high-temperature deformation are still discussed controversially. This study reveals that for plastic strains of up to 3.2 %, dislocations carry plasticity in superalloy single crystals compressed at high temperatures, and that both dislocations as well as superlattice stacking faults can be easily annealed out by recovery treatment to preempt recrystallization. This means that the recoverability of Ni-based superalloy single crystals can be increased by more than twice compared to previous reports. For larger plastic strains, deformation twins form. They block moving dislocations which assemble in new boundaries that eventually trigger dynamic recrystallization. Upon subsequent heat treatment, such newly recrystallized grains grow rapidly further, resulting in a coarse polycrystalline microstructure. Consequently, avoiding deformation twins becomes the key to maintaining the single-crystalline microstructure.