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Fermi liquids and metallic ferromagnetism The low-temperature properties of conventional metals are well described by Fermi liquid theory, which treats electrons as a gas of scattering but otherwise non-interacting entities. But increasingly, examples of metallic systems are being found in which Fermi liquid theory breaks down, often in mysterious ways. Smith et al. describe one such example in which non-Fermi liquid properties can be attributed to a specific process — the long-range interactions between the electronic spins in a metal on the verge of becoming magnetic. Such a system is known as a 'marginal' Fermi liquid, and provides a conceptual link between classical metals and more exotic non-Fermi systems. For the past half century, our understanding of how the interactions between electrons affect the low-temperature properties of metals has been based on the Landau theory of a Fermi liquid 1 . In recent times, however, there have been an increasingly large number of examples in which the predictions of the Fermi-liquid theory appear to be violated 2 . Although the qualitative reasons for the breakdown are generally understood, the specific quantum states that replace the Fermi liquid remain in many cases unclear. Here we describe an example of such a breakdown where the non-Fermi-liquid properties can be interpreted. We show that the thermal and electrical resistivities in high-purity samples of the d -electron metal ZrZn 2 at low temperatures have T and T 5/3 temperature dependences, respectively: these are the signatures of the ‘marginal’ Fermi-liquid state 3 , 4 , 5 , 6 , 7 , expected to arise from effective long-range spin–spin interactions in a metal on the border of metallic ferromagnetism in three dimensions 3 , 5 . The marginal Fermi liquid provides a link between the conventional Fermi liquid and more exotic non-Fermi-liquid states that are of growing interest in condensed matter physics. The idea of a marginal Fermi liquid has also arisen in other contexts—for example, in the phenomenology of the normal state of the copper oxide superconductors 7 , and in studies of relativistic plasmas and of nuclear matter 3 , 4 , 6 .

Sodium under pressure It has recently been shown that, when high pressures are applied, crystals of lithium and sodium undergo a sequence of phase transitions — including (for sodium) a striking and as yet unexplained pressure-induced drop in the melting temperature. Jean-Yves Raty et al . have now identified the cause of this unusual melting behaviour: it emerges because liquid sodium undergoes a series of transitions similar to those seen in the solid state, but at much lower pressures. Intriguingly, one of these transitions is driven by the opening of a 'pseudogap' in the electronic density of states, the first time such an effect has been seen in a liquid metal. When high pressures are applied, crystals of lithium and sodium undergo a sequence of phase transitions, including a striking pressure-induced drop in the melting temperature. The cause of the unusual melting behaviour has now been identified: it emerges because liquid sodium undergoes a series of transitions similar to those seen in the solid state, but at much lower pressures. One of these transitions is driven by the opening of a 'pseudogap' in the electronic density of states. At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure 1 , 2 , 3 , 4 , 5 , 6 . It was predicted from theory 1 , 2 —and later confirmed by experiment 3 , 4 , 5 —that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve 6 have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states—an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well.

Methods used to strengthen metals generally also cause a pronounced decrease in electrical conductivity, so that a tradeoff must be made between conductivity and mechanical strength. We synthesized pure copper samples with a high density of nanoscale growth twins. They showed a tensile strength about 10 times higher than that of conventional coarse-grained copper, while retaining an electrical conductivity comparable to that of pure copper. The ultrahigh strength originates from the effective blockage of dislocation motion by numerous coherent twin boundaries that possess an extremely low electrical resistivity, which is not the case for other types of grain boundaries.

Traditional metallic alloys are mixtures of elements in which the atoms of minority species tend to be distributed randomly if they are below their solubility limit, or to form secondary phases if they are above it. The concept of multiple-principal-element alloys has recently expanded this view, as these materials are single-phase solid solutions of generally equiatomic mixtures of metallic elements. This group of materials has received much interest owing to their enhanced mechanical properties 1 – 5 . They are usually called medium-entropy alloys in ternary systems and high-entropy alloys in quaternary or quinary systems, alluding to their high degree of configurational entropy. However, the question has remained as to how random these solid solutions actually are, with the influence of short-range order being suggested in computational simulations but not seen experimentally 6 , 7 . Here we report the observation, using energy-filtered transmission electron microscopy, of structural features attributable to short-range order in the CrCoNi medium-entropy alloy. Increasing amounts of such order give rise to both higher stacking-fault energy and hardness. These findings suggest that the degree of local ordering at the nanometre scale can be tailored through thermomechanical processing, providing a new avenue for tuning the mechanical properties of medium- and high-entropy alloys. Metal alloys consisting of three or more major elemental components show enhanced mechanical properties, which are now shown to be correlated with short-range order observed with electron microscopy.

Alloys with ultra-high strength and sufficient ductility are highly desired for modern engineering applications but difficult to develop. Here we report that, by a careful controlling alloy composition, thermomechanical process, and microstructural feature, a Co-Cr-Ni-based medium-entropy alloy (MEA) with a dual heterogeneous structure of both matrix and precipitates can be designed to provide an ultra-high tensile strength of 2.2 GPa and uniform elongation of 13% at ambient temperature, properties that are much improved over their counterparts without the heterogeneous structure. Electron microscopy characterizations reveal that the dual heterogeneous structures are composed of a heterogeneous matrix with both coarse grains (10∼30 μm) and ultra-fine grains (0.5∼2 μm), together with heterogeneous L1 2 -structured nanoprecipitates ranging from several to hundreds of nanometers. The heterogeneous L1 2 nanoprecipitates are fully coherent with the matrix, minimizing the elastic misfit strain of interfaces, relieving the stress concentration during deformation, and playing an active role in enhanced ductility. Improving both strength and ductility simultaneously in structural metals and alloys remains a challenge. Here, the authors design a heterogeneous structure in a Co-Cr-Ni alloy that results in ultrahigh strength and significant uniform elongation.

Explore the world of advanced materials and their manufacturing processes through this authoritative and enlightening reference. Discover how these innovations are shaping the future of high-tech industries and making a profound impact on our world. Manufacturing and Processing of Advanced Materials compiles current research and updates on development efforts in advanced materials, manufacturing, and their engineering applications. The book presents 22 peer-reviewed chapters that cover new materials and manufacturing processes. Key Topics Materials for the Future: Properties, classifications, and harmful effects of advanced engineering Innovative Manufacturing Techniques: Nanotechnology in material processing and manufacturing innovation. Advanced Welding and Joining: laser welding and friction stir welding in manufacturing composite materials. Sustainable Practices: Eco-Friendly machining, water vapor cutting fluid, for high-speed milling, natural fiber reinforcement with materials like bamboo leaves. Advanced Materials Characterization and Modeling: Carbon nanotube (CNT)-reinforced nanocomposites and tribology for durable and reliable materials ensuring reliability. Materials for Energy and Electronics: Energy Storage Innovations and smart materials for electronic devices Novel Drilling and Machining Processes: Microwave drilling, electric discharge machining and die-sinking electric discharge machining for metal matrix composites. Innovations in Nanoparticle Production: Spark discharge method (SDM) for advanced nanoparticle production. The book caters to a diverse audience, offering an invaluable resource for researchers, engineers, graduate students, and professionals in materials science, engineering, chemistry, and physics. By enhancing their knowledge and expertise, readers are poised to become key contributors to various industries and technological advancements.

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. Tungsten-based alloys with ultrahigh strength and ductility are in high demand for a wide range of applications, potentially for fusion reactors. Here the authors develop a tungsten refractory high-entropy alloy with high strength (~2.15 GPa) and sufficient ductility (~15%).

A special case of equality of the conduction current density and the displacement current density in a homogeneous nonmagnetic conducting medium was used to consider the results of approximate calculation estimation of the relative permittivity ε r of nonmagnetic conducting materials (metals and alloys), which are extensively used in electrical power engineering, electric power industry, and high-voltage pulse technology under the influence of variable (pulsed) electric currents and electromagnetic fields (EMF) with various amplitude–time parameters. It was demonstrated that, in the investigated case, at low frequencies f 0 of conduction current and EMF (at a frequency on the order of 10 2 Hz) in the range of extremely low-frequency electromagnetic waves (EMW), the materials under consideration exhibit extremely high values of the electrophysical parameter ε r (on the order of 10 15 ). For extremely high frequencies f 0 of current and EMF (at a frequency on the order of 5 × 10 13 Hz) in the infrared range of EMW, these conducting materials are characterized by ε r values on the order of 10 2 –10 4 , and in terms of the electrophysical parameter ε r , they approach solid dielectrics and ferroelectrics.

Developing affordable and light high-temperature materials alternative to Ni-base superalloys has significantly increased the efforts in designing advanced ferritic superalloys. However, currently developed ferritic superalloys still exhibit low high-temperature strengths, which limits their usage. Here we use a CALPHAD-based high-throughput computational method to design light, strong, and low-cost high-entropy alloys for elevated-temperature applications. Through the high-throughput screening, precipitation-strengthened lightweight high-entropy alloys are discovered from thousands of initial compositions, which exhibit enhanced strengths compared to other counterparts at room and elevated temperatures. The experimental and theoretical understanding of both successful and failed cases in their strengthening mechanisms and order-disorder transitions further improves the accuracy of the thermodynamic database of the discovered alloy system. This study shows that integrating high-throughput screening, multiscale modeling, and experimental validation proves to be efficient and useful in accelerating the discovery of advanced precipitation-strengthened structural materials tuned by the high-entropy alloy concept. Advanced screening strategies for the design of high-entropy alloys are highly desirable. Here the authors use the project-oriented design strategy and CALPHAD-based high-throughput calculation tool to rapidly screen promising Al-Cr-Fe-Mn-Ti structural HEAs for high-temperature applications.

In conventional processing, metals go through multiple manufacturing steps including casting, plastic deformation, and heat treatment to achieve the desired property. In additive manufacturing (AM) the same target must be reached in one fabrication process, involving solidification and cyclic remelting. The thermodynamic and kinetic differences between the solid and liquid phases lead to constitutional undercooling, local variations in the solidification interval, and unexpected precipitation of secondary phases. These features may cause many undesired defects, one of which is the so-called hot cracking. The response of the thermodynamic and kinetic nature of these phenomena to high cooling rates provides access to the knowledge-based and tailored design of alloys for AM. Here, we illustrate such an approach by solving the hot cracking problem, using the commercially important IN738LC superalloy as a model material. The same approach could also be applied to adapt other hot-cracking susceptible alloy systems for AM. Production defects prevent many industrially important materials from being adopted by metal additive manufacturing. Here, the authors propose a universal thermodynamics-guided alloy design approach to assist the discovery of crack-free materials.