High-entropy alloys (HEAs) have gained substantial attention over the past two decades, necessitating a comprehensive understanding of their intrinsic and extrinsic properties, including mechanical behavior, creep resistance, phase stability, environmental degradation, etc. Among these, atomic transport mechanisms, particularly along grain boundaries (GBs) play a pivotal role in determining material performance. This review critically evaluates the “sluggish” diffusion concept, focusing on its validity and applicability to GB diffusion in HEAs. It examines the influences of GB complexions, segregation phenomena, and precipitation processes on GB diffusion behavior in HEAs, comparing them with their counterparts in conventional binary and ternary alloys, both dilute and concentrated. The inherent challenges in accurately characterizing GB diffusion in multi-principal element alloys, given their broad compositional variability and complex microstructures are also highlighted. The contribution of inter-phase boundary diffusion in multi-component alloy systems is also identified and analyzed. Furthermore, the broader implications of GB diffusion on the mechanical and physical properties of polycrystalline HEAs are discussed in terms of their strength, ductility, and degradation resistance. By consolidating the current state of research on GB diffusion in HEAs and identifying the key research gaps, this review aims to catalyze focused and intensive research efforts into diffusion-related phenomena in HEAs and other compositionally complex alloys. Emphasis is placed on comprehensive understanding the interplay between GB structure, chemistry, and atomic transport phenomena to enable effective GB engineering stategies for these alloys. Insights from such studies will be instrumental in optimizing HEAs for advanced technological applications and in guiding the development of next-generation high-performance materials.

This review compares the microstructural defects and mechanical properties of WC-Co cemented carbides fabricated by beam-based additive manufacturing (BBAM) and sinter-based additive manufacturing (SBAM) technologies. BBAM methods, such as selective laser melting (SLM), use high-energy sources to melt powder layers, often leading to non-equilibrium phases, carbon/cobalt depletion, and inhomogeneous microstructures marked by alternating distributions of fine and coarse WC grains. These processes also introduce residual stress and brittleness due to non-uniform heating and rapid cooling. In contrast, SBAM methods, including binder jetting (BJT), yield microstructures resembling those of traditionally sintered materials, with improved consistency. While BBAM-processed parts typically suffer from porosity, cracks, and brittle phases, optimized SBAM-processed cemented carbides demonstrate fewer defects, though interlayer cracking remains a challenge. Mechanically, BBAM excels in fabricating intricate, high-precision components where hardness and wear resistance are critical. Conversely, SBAM is better suited for producing larger, geometrically complex parts requiring uniform microstructures and enhanced strength. Both approaches offer complementary advantages for specific applications in cemented carbide additive manufacturing. Future research should focus on refining additive manufacturing technologies and powder formulation techniques to minimize defects, improve dimensional accuracy, and enhance the mechanical performance, particularly strength, in fabricated cemented carbides.

Ultrasonic processing in the liquid state has been identified as an effective method to improve the mechanical properties of Al and Mg alloys. Ultrasonic melt processing is capable of enhancing material properties through the application of high-frequency, high-power vibrations that form cavitation bubbles which pulsate and collapse throughout the melt volume. Thus, this technology has excellent potential in engineering high performance lightweight materials. With global trends converging toward greener energy, reduced greenhouse gas (GHG) emissions and increasingly stringent efficiency standards, lightweight and high-strength alloys such as aluminum (Al) and magnesium (Mg) are becoming an area of high interest. The aim of this review is to analyze the literature on ultrasonic processing of Al and Mg alloys in the last 15 years. This review discusses ultrasonic processing equipment, experimental set-ups, mechanisms of ultrasonic cavitation and acoustic streaming. As well, the effects of processing time, vibrational amplitude, and temperature on microstructure and properties are elucidated. Furthermore, it aims to investigate how a combination of sonication and particle reinforcement can affect the properties of Al and Mg alloys. The challenges of ultrasonic processing have been identified and expanded on in this review. This includes energy consumption, equipment complexity, temperature control, process optimization and limited industrial adoption.

By control of their constituents, interfaces and architectures, composite materials can display a much broader suite of beneficial material properties than is possible for single-phase materials. Furthermore, advanced manufacturing techniques are increasing the freedom to operate of composite designers. While much can be achieved with idealised models of composites, models are needed that more accurately reflect the non-ideal placement of reinforcement, matrix-free regions and manufacturing defects that occur in practice. At the same time, imaging techniques, and X-ray computed tomography in particular, have radically increased the level of information that can be obtained in three dimensions and over time about real composite microstructures, both about the as-manufactured condition and their behaviour in-service. This review considers all aspects of image-based modelling of composite materials across the length scales. It also discusses establishing the appropriate constitutive equations for deterministic and stochastic (e.g., fibre fractures) elements of behaviour, as well as methods for validation. A range of actual and potential applications from the literature are showcased throughout. It explores approaches to bridging the scales and techniques, such as surrogate and homogenised models, to ensure models are computationally feasible. It covers a wide range of composites, spanning polymer, metal and ceramic matrices, continuous and short fibres, as well as particulate reinforcements. It also briefly extends to how such approaches can be applied to other ‘composite’ systems, such as concrete and hard metals. Overall, this is a one-stop review for those considering multiscale modelling of composites based on realistic, often multiscale, composite architectures.

Thermal energy conversion using non-linear pyroelectric materials present a sustainable solution for transforming waste heat into useful energy. By utilizing the temperature and electric field dependence of these materials, heat can be directly converted into electrical energy. This review explores non-linear pyroelectric energy conversion, highlighting the use of ferroelectric materials and their non-linear behaviour in thermal energy harvesting. In this work, we critically examine the materials, thermodynamic cycles for pyroelectric energy conversion, figures-of-merit for pyroelectric energy harvesting, and the influence of material geometry, aging and conversion losses. The primary objective of this review is to emphasize the importance of power generation through pyroelectric modules and re-examine the scope of macroscopic pyroelectric energy harvesters for practical applications. Concepts related to macroscopic devices such as regeneration and heat exchange conditions using thermal control elements for thermal energy harvesting are also discussed. This article aims to provide a comprehensive overview of the advancements, challenges, and future directions in the field of non-linear pyroelectric energy harvesting.

Functionally graded materials (FGMs) are special advanced composite materials. The significant capabilities of additive manufacturing (AM) technology in material and structural control offer promising opportunities for designing and fabricating next-generation FGMs. However, the current fabrication of FGMs using AM technology (AM-FGMs) is often relies on empirical methodologies, limiting the exploitation of the distinctive features of high-performance FGMs. Therefore, we propose a "bottom-to-top" design concept for AM-FGMs aimed at achieving high performance, versatility, and suitability for industrial applications in extreme environments, integrating optimal design with AM technology. Initially, this paper discusses the optimal design of AM-FGMs, emphasizing multi-scale and multi-functional design driven by AM technology. Subsequently, the advantages and disadvantages of different AM-FGMs fabrication methods, process optimization, and post-processing optimization are discussed. Finally, the versatile applications, research challenges, and prospects of AM-FGMs are summarized. This work contributes to advancing the realization of high-performance AM-FGMs and offers valuable guidance for the fabrication in the future.

Reticulation chemistry provides new ideas for the development of new composite materials. In recent years, many researchers have taken advantage of the large specific surface area, high porosity, easy chemical functionalization, and good nanostructure design of reticular materials to study the flame retardant effect and mechanism of reticular materials in various polymer materials, and mainly utilized the properties of metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs) to apply them to a variety of polymers, and design polymer composites with enhanced flame retardant properties. The design of reticular composites is a new solution to improve the combustion performance of polymer composites, and thus a comprehensive and systematic study of them is highly desirable. To the best of our knowledge, there is no review on the research progress of reticular materials in the field of flame retardancy, so this paper provides a comprehensive overview of the research progress of MOFs, COFs and HOFs in flame retardant polymer materials in recent years. Mainly focusing on polymers such as epoxy resins and polyurethanes, we analyze the modification strategies and flame retardant effects of these three materials in the corresponding polymer materials. We compared the advantages and disadvantages of the three materials in terms of synthesis methods, structural design and application prospects. Finally, we will discuss in detail the challenges and limitations of using reticular materials in flame-retardant polymers based on an analysis of scalability, cost, and long-term stability.

Titanium (Ti) and its alloys are widely used in orthopedic and dental implants owing to their high biocompatibility with tissues, low toxicity, and excellent mechanical properties, such as high strength, fatigue strength, and corrosion resistance. Total hip arthroplasty (THA) is predicted to rise from1.8 million in 2015 to 2.8 million in 2050, and the demand for Ti-based THA is also increasing. The biocompatibility of Ti originates from the several-nanometer-thick oxide layer present on its surface, which inhibits the redox reactions. The oxide forms spontaneously on the surface upon exposure to air and stays in thermodynamic equilibrium; however, it is easily disrupted by the interfacial shear stress owing to the low wear resistance of Ti. Ti exposed to corrosive body fluids elutes metal ions, generating wear debris in the biological fluids and tissues. This causes injury and disease, incites allergies, and promotes the formation of granulomas and even carcinomas. Furthermore, poor osseointegration due to poor adhesion with adjacent bone causes the loosening of the implant-bone interface and slows the healing process. To overcome these drawbacks of implant Ti materials, surface modifications using biocompatible TiO 2 are expected for imparting biofunctions such as osseointegration, antivirus activity, and tribocorrosion. Although various methods have been studied for the fabrication of TiO 2 on Ti alloys, anodic oxidation has attracted considerable attention owing to its advantages. This review aims to provide a comprehensive, evidence-based overview of current studies on the osseointegration, antimicrobial properties, and cytotoxicity of surface-modified implant Ti alloys, in addition to a brief introduction to different metallic biomaterials.

Polyacrylonitrile-based carbon fibers (PANCFs) have revolutionized industries since the 1960s due to their superior properties and applications. However, a significant gap remains between their performance and theoretical potential, highlighting the urgent need to enhance our understanding of the process-structure-performance relationship. Computational simulations, with their ability to provide analysis from the atomic level to higher-scale, are essential for bridging this gap. This review provides a comprehensive overview of advancements in computational simulation techniques to produce high-performance PANCFs by optimizing the process parameters through simulations. Furthermore, advancements in reactive molecular dynamics, density functional theory, atomistic modelling, and finite element methods to enhance the PANCFs manufacturing process are systematically evaluated. Simulations play an important role in developing PANCFs by identifying novel comonomers for PAN precursors, evaluating different solvents during spinning, precise tracking of cyclization and dehydrogenation mechanisms during stabilization, and predicting mechanical property losses due to defects. Moreover, it is demonstrated that how kinetics-driven frameworks accelerate carbonization simulations by combining atomic-scale interactions such as carbon ring formation and graphitic growth with macroscale process parameters like temperature and pressure. However, certain limitations remain: unresolved heterogeneous microstructure representation, multiscale disconnects between atomic bond-breaking and macroscopic fiber evolution, and validation barriers due to oversimplified quasi-2D models. To overcome these problems, possible future directions including advanced force fields, multiscale integration, and AI-driven modeling could enhance the performance of PANCFs.

As the exigency for decarbonizing sectors such as utilities, heavy-duty transportation, and manufacturing has risen, interest in hydrogen technologies has intensified accordingly. Among the safety issues being addressed for hydrogen technologies is the potential for hydrogen embrittlement of steels, which are commonly specified for pressure boundaries in containment components. From an engineering perspective, hydrogen embrittlement of steels can be managed through conventional design and fitness-for-service (FFS) practices provided the mechanical property inputs are measured appropriately, i.e., testing of steels is performed in the hydrogen environment. Given the increasing need for managing hydrogen embrittlement to safely operate high-pressure containment components, the purpose of this review is to comprehensively survey and critically assess the literature on the following mechanical properties of steels in gaseous hydrogen that serve as inputs to design and FFS analyses: threshold stress-intensity factor or threshold J-integral for subcritical, time-dependent cracking, fatigue crack growth rate, and total fatigue life. The review focuses on such mechanical properties in gaseous hydrogen for carbon-manganese (C-Mn) steels, low-alloy steels, austenitic stainless steels, duplex stainless steels, as well as the ferritic and martensitic stainless steels, since these are most pertinent to containment components in hydrogen technology. Three high-level conclusions from the review are the following: 1) mechanical property data for C-Mn and low-alloy steels in hydrogen gas are sufficiently mature so that conservative limits can be specified for design and FFS analyses, 2) mechanical property data for austenitic stainless steels must be supplemented with additional measurements, particularly from specimens tested in high-pressure hydrogen gas, before conservative limits can be defined for design and FFS analyses, and 3) mechanical property data for ferritic, martensitic, and duplex stainless steels in hydrogen gas are so scarce that design and FFS analyses covering wide ranges of steel grades and component service conditions are currently not feasible.