Explore the vast range of titles available.

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. The four core effects of high-entropy alloys are discussed and greater insights are presented. These clarifications are helpful in understanding materials from low entropy (simple two-component or three-component alloys) to high entropy (five components or greater), and in general materials design.

Hypersonic vehicles must withstand extreme conditions during flights that exceed five times the speed of sound. These systems have the potential to facilitate rapid access to space, bolster defense capabilities, and create a new paradigm for transcontinental earth-to-earth travel. However, extreme aerothermal environments create significant challenges for vehicle materials and structures. This work addresses the critical need to develop resilient refractory alloys, composites, and ceramics. We will highlight key design principles for critical vehicle areas such as primary structures, thermal protection, and propulsion systems; the role of theory and computation; and strategies for advancing laboratory-scale materials to manufacturable flight-ready components. Hypersonic vehicles experience extreme temperatures, high heat fluxes, and aggressive oxidizing environments. Here, the authors highlight key materials design principles for critical vehicle areas and strategies for advancing laboratory-scale materials to flight-ready components.

Strain-hardening (the increase of flow stress with plastic strain) is the most important phenomenon in the mechanical behaviour of engineering alloys because it ensures that flow is delocalized, enhances tensile ductility and inhibits catastrophic mechanical failure 1 , 2 . Metallic glasses (MGs) lack the crystallinity of conventional engineering alloys, and some of their properties—such as higher yield stress and elastic strain limit 3 —are greatly improved relative to their crystalline counterparts. MGs can have high fracture toughness and have the highest known ‘damage tolerance’ (defined as the product of yield stress and fracture toughness) 4 among all structural materials. However, the use of MGs in structural applications is largely limited by the fact that they show strain-softening instead of strain-hardening; this leads to extreme localization of plastic flow in shear bands, and is associated with early catastrophic failure in tension. Although rejuvenation of an MG (raising its energy to values that are typical of glass formation at a higher cooling rate) lowers its yield stress, which might enable strain-hardening 5 , it is unclear whether sufficient rejuvenation can be achieved in bulk samples while retaining their glassy structure. Here we show that plastic deformation under triaxial compression at room temperature can rejuvenate bulk MG samples sufficiently to enable strain-hardening through a mechanism that has not been previously observed in the metallic state. This transformed behaviour suppresses shear-banding in bulk samples in normal uniaxial (tensile or compressive) tests, prevents catastrophic failure and leads to higher ultimate flow stress. The rejuvenated MGs are stable at room temperature and show exceptionally efficient strain-hardening, greatly increasing their potential use in structural applications. Bulk metallic glasses can acquire the ability to strain-harden through a mechanical rejuvenation treatment at room temperature that retains their non-crystalline structure.

Realizing improved strength–ductility synergy in eutectic alloys acting as in situ composite materials remains a challenge in conventional eutectic systems, which is why eutectic high-entropy alloys (EHEAs), a newly-emerging multi-principal-element eutectic category, may offer wider in situ composite possibilities. Here, we use an AlCoCrFeNi 2.1 EHEA to engineer an ultrafine-grained duplex microstructure that deliberately inherits its composite lamellar nature by tailored thermo-mechanical processing to achieve property combinations which are not accessible to previously-reported reinforcement methodologies. The as-prepared samples exhibit hierarchically-structural heterogeneity due to phase decomposition, and the improved mechanical response during deformation is attributed to both a two-hierarchical constraint effect and a self-generated microcrack-arresting mechanism. This work provides a pathway for strengthening eutectic alloys and widens the design toolbox for high-performance materials based upon EHEAs. Producing in situ composite materials with superior strength and ductility has long been a challenge. Here, the authors use lamellar microstructure inherited from casting, rolling, and annealing to produce an ultrafine duplex eutectic high entropy alloy with outstanding properties.

It has been known for decades that the application of pulsed direct current can significantly enhance the formability of metals. However, the detailed mechanisms of this effect have been difficult to separate from simple Joule heating. Here, we study the electroplastic deformation of Ti–Al (7 at.% Al), an alloy that is uniquely suited for uncoupling this behaviour because, contrary to most metals, it has inherently lower ductility at higher temperature. We find that during mechanical deformation, electropulsing enhances cross-slip, producing a wavy dislocation morphology, and enhances twinning, which is similar to what occurs during cryogenic deformation. As a consequence, dislocations are prevented from localizing into planar slip bands that would lead to the early failure of the alloy under tension. Our results demonstrate that this macroscopic electroplastic behaviour originates from defect-level microstructural reconfiguration that cannot be rationalized by simple Joule heating. Transmission electron microscopy reveals the electroplastic effects in a Ti–Al alloy, which can be uncoupled from Joule heating effects. Electropulsing during deformation enhances wavy slip of dislocations, reconfiguring the dislocation pattern, and hence increases the ductility.

Magnesium is light but not very strong; here the addition of silicon carbide nanoparticles uniformly dispersed to 14 per cent by volume, achieved through a nanoparticle self-stabilization mechanism in a molten metal alloy, yields improved strength, stiffness, plasticity and high-temperature stability. A new route to magnesium alloy composites The best magnesium alloys currently available are remarkably light but lack the strength offered by other structural metals. Magnesium-based composites could provide a way of retaining lightness while adding strength. Here Xiao-Chun Li and colleagues demonstrate the production of a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium via nanoparticle self-stabilization in molten metal. The resulting composite has improved strength, stiffness, plasticity and high-temperature stability. By overcoming the long-standing challenge of dispersing nanoparticles in metal matrices, this new approach may offer a widely applicable route to high-performance light-metal composites. Magnesium is a light metal, with a density two-thirds that of aluminium, is abundant on Earth and is biocompatible; it thus has the potential to improve energy efficiency and system performance in aerospace, automobile, defence, mobile electronics and biomedical applications 1 , 2 , 3 , 4 , 5 . However, conventional synthesis and processing methods (alloying and thermomechanical processing) have reached certain limits in further improving the properties of magnesium and other metals 6 . Ceramic particles have been introduced into metal matrices to improve the strength of the metals 7 , but unfortunately, ceramic microparticles severely degrade the plasticity and machinability of metals 7 , and nanoparticles, although they have the potential to improve strength while maintaining or even improving the plasticity of metals 8 , 9 , are difficult to disperse uniformly in metal matrices 10 , 11 , 12 , 13 , 14 . Here we show that a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium can be achieved through a nanoparticle self-stabilization mechanism in molten metal. An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals.

Rejuvenation of metallic glasses, bringing them to higher-energy states, is of interest in improving their plasticity. The mechanisms of rejuvenation are poorly understood, and its limits remain unexplored. We use constrained loading in compression to impose substantial plastic flow on a zirconium-based bulk metallic glass. The maximum measured effects are that the hardness of the glass decreases by 36%, and its excess enthalpy (above the relaxed state) increases to 41% of the enthalpy of melting. Comparably high degrees of rejuvenation have been reported only on microscopic scales at the centre of shear bands confined to low volume fractions. This extreme rejuvenation of a bulk glass gives a state equivalent to that obtainable by quenching the liquid at ~10 10  K s –1 , many orders of magnitude faster than is possible for bulk specimens. The contrast with earlier results showing relaxation in similar tests under tension emphasizes the importance of hydrostatic stress. Deforming metallic glasses can rejuvenate them to higher energy states, but only in the shear bands where deformation is usually concentrated. Here, the authors use a notched setup to suppress shear banding and promote significant bulk softening of a zirconium-based metallic glass.

B1-type TiC compounds in equilibrium with metal solid solution phases can possess off-stoichiometry allowing them to exhibit different mechanical properties compared to those containing stoichiometric TiC, which typically decreases the toughness of the material. In this study, the fracture behavior of Mo/(Ti 0.96 ,Mo 0.04 )C 0.67 two-phase alloys was investigated. The load–displacement curves of the Mo/(Ti 0.96 ,Mo 0.04 )C 0.67 two-phase alloys, as measured by four-point bending tests, were similar regardless of the (Ti 0.96 ,Mo 0.04 )C 0.67 volume fraction , whereas the peak stress and fracture toughness increased with increasing volume fraction. These results suggest that (Ti 0.96 ,Mo 0.04 )C 0.67 acts as both a strengthening and toughening phase. Two factors are considered to contribute to its function as a toughening phase: the presence of the Mo phase within the (Ti 0.96 ,Mo 0.04 )C 0.67 grains, and the improvement in the deformability of (Ti,Mo)C x itself owing to its off-stoichiometry.

This work aims to scrutinize the effect of the silanization of glass fibers (GF) on the mechanical properties and cathodic disbonding resistance of an epoxy composite coating. Successful silanization was approved based on different characterization techniques, including Fourier transform infrared spectra, field emission-scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. Tensile strength measurement exhibited a significant effect of silanization on the mechanical performance of the fiber-reinforced polymer (FRP). FE-SEM cross-sectional images illustrated improved interfacial bonding between the epoxy matrix and GF upon silanization. Pull-off measurements revealed improved wet adhesion strength of the FRP to the mild steel surface after exposure to the salt spray chamber when the GF were silanized. In addition, silanization revealed enhanced resistance to cathodic delamination (CD). Electrochemical impedance spectroscopy and electrochemical noise assessments proved silanization's significant influence on the FRP's CD resistance.

Novel metal matrix composites (MMCs) have been fabricated with Ti6Al4V matrix and a biogenic ceramic filler in the form of diatomaceous earth (DE). Mixtures of DE and Ti6Al4V powders were consolidated by the spark plasma sintering (SPS) method. Microstructure of the consolidated samples has been investigated with microscopic techniques and XRD. Thermomechanical characteristics have been obtained using small-sample techniques. The results obtained indicate that the fabricated composites show outstanding mechanical and thermal properties due to synergic effects between the filler and the matrix (beyond the rule of mixtures).