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High-strength steel fasteners characterized by tensile strengths above 1100 MPa are often used in critical applications where a failure can have catastrophic consequences. Preventing hydrogen embrittlement (HE) failure is a fundamental concern implicating the entire fastener supply chain. Research is typically conducted under idealized conditions that cannot be translated into know-how prescribed in fastener industry standards and practices. Additionally, inconsistencies and even contradictions in fastener industry standards have led to much confusion and many preventable or misdiagnosed fastener failures. HE susceptibility is a function of the material condition, which is comprehensively described by the metallurgical and mechanical properties. Material strength has a first-order effect on HE susceptibility, which increases significantly above 1200 MPa and is characterized by a ductile--brittle transition. For a given concentration of hydrogen and at equal strength, the critical strength above which the ductile-brittle transition begins can vary due to second-order effects of chemistry, tempering temperature and sub-microstructure. Additionally, non-homogeneity of the metallurgical structure resulting from poorly controlled heat treatment, impurities and non-metallic inclusions can increase HE susceptibility of steel in ways that are measurable but unpredictable. Below 1200 MPa, non-conforming quality is often the root cause of real-life failures. This article is part of the themed issue ‘The challenges of hydrogen and metals’.

Significant advances in the study of liquid metal embrittlement have occurred since 2000 but there have been few reviews of the liquid metal embrittlement literature since that time. This review discusses recent advances in modeling and testing. Specific solid–liquid systems (including steel exposed to molten lead–bismuth and aluminum–gallium) are reviewed. Relationships between various studies are considered and the need for careful test protocols is emphasized. The individual effects of wetting, crack initiation, and propagation are discussed. Mechanisms of liquid metal embrittlement including interatomic and mass transport-based phenomena are analyzed.

Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in α-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle-cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials. Hydrogen embrittlement in metals has proved problematic for designing strong and reliable structural materials. Direct molecular dynamics simulations now reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to the aggregation of hydrogen.

Hydrogen’s wide availability and versatile production methods establish it as a primary green energy source, driving substantial interest among the public, industry, and governments due to its future fuel potential. Notable investment is directed toward hydrogen research and material innovation for transmission, storage, fuel cells, and sensors. Ensuring safe and dependable hydrogen facilities is paramount, given the challenges in accident control. Addressing material compatibility issues within hydrogen systems remains a critical focus. Challenges, roadmaps, and scenarios steer long-term planning and technology outlooks. Strategic visions align actions and policies, encompassing societal and ecological dimensions. The confluence of hydrogen’s promise with material progress holds the prospect of reshaping our energy landscape sustainably. Forming collective future perspectives to foresee this emerging technology’s potential benefits is valuable. Our review article comprehensively explores the forthcoming challenges in hydrogen technology. We extensively examine the challenges and opportunities associated with hydrogen production, incorporating CO2 capture technology. Furthermore, the interaction of materials and composites with hydrogen, particularly in the context of hydrogen transmission, pipeline, and infrastructure, are discussed to understand the interplay between materials and hydrogen dynamics. Additionally, the exploration extends to the embrittlement phenomena during storage and transmission, coupled with a comprehensive examination of the advancements and hurdles intrinsic to hydrogen fuel cells. Finally, our exploration encompasses addressing hydrogen safety from an industrial perspective. By illuminating these dimensions, our article provides a panoramic view of the evolving hydrogen landscape.

A thickness-dependent metric allows for comparison of materials for device applications Flexible materials are widely used in health care, robotics, and other industries, but flexible electronic devices require that normally brittle electronic materials become flexible. Stiff materials can become flexible if they are sufficiently thin. Future applications, such as energy systems for the internet-of-things, will likely require new materials where trade-offs in performance and flexibility must be weighed with a metric of flexibility. The yield strain ϵ y —that is, how much a material can stretch elastically (still recover its shape) before deforming plastically (stretching it out of shape)—for a given thickness of a material can serve as a figure of merit (FOM) for flexibility ( f FoM ).

Hydrogen embrittlement is a common, dangerous, and poorly understood cause of failure in many metal alloys. In practice, it is observed that different types of damage to industrial components have been tied to the presence and localization of hydrogen in metals. Many efforts have been made at understanding the effects of hydrogen on materials, resulting in an abundance of theoretical models and papers. However, a fully developed and practically-applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen embrittlement. The connection of microstructure-based behaviors of materials and effects on the macroscopic measurable characteristics (stress levels, hardness, strength, and impact toughness) is of the utmost importance to achieve a unified model for hydrogen embrittlement. This paper gives an overview of the application of a model for structural integrity analysis of boiler tubes made of plain carbon steel exposed during operation to a local corrosion process and multiple hydrogen assisted degradation processes: hydrogen embrittlement and high-temperature hydrogen attack. The model is based on the correlation of mechanical properties to scanning electron microscopy fractography analysis of fracture surfaces in the presence of simultaneously active hydrogen embrittlement micro-mechanisms. The proposed model is practical for use as a predictive maintenance in power plants, as it is based on the use of standard macro-mechanical tests.

Improving the strength of a metal alloy is hard to do without sacrificing the ductility. Yang et al. designed an iron-nickel-cobalt (Fe-Ni-Co) alloy laced with aluminum-titanium (Al-Ti) nanoparticles with both high strength and ductility. The key was getting the composition tuned correctly, because the Fe-Ni-Co matrix reacts with the Al-Ti nanoparticles. This was vital for avoiding environmental embrittlement, enhancing work hardening, and improving ductility. Science , this issue p. 933 Multicomponent nanoparticles enhance both the strength and ductility of an iron-nickel-cobalt alloy. Alloy design based on single–principal-element systems has approached its limit for performance enhancements. A substantial increase in strength up to gigapascal levels typically causes the premature failure of materials with reduced ductility. Here, we report a strategy to break this trade-off by controllably introducing high-density ductile multicomponent intermetallic nanoparticles (MCINPs) in complex alloy systems. Distinct from the intermetallic-induced embrittlement under conventional wisdom, such MCINP-strengthened alloys exhibit superior strengths of 1.5 gigapascals and ductility as high as 50% in tension at ambient temperature. The plastic instability, a major concern for high-strength materials, can be completely eliminated by generating a distinctive multistage work-hardening behavior, resulting from pronounced dislocation activities and deformation-induced microbands. This MCINP strategy offers a paradigm to develop next-generation materials for structural applications.

Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles 1 . High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation 2 , 3 . Hydrogen ‘embrittlement’ is often indicated as the main culprit 4 ; however, the exact mechanisms underpinning failure are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the durability of the materials. Here we performed near-atomic-scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We used these observations to guide atomistic ab initio calculations, which show that the co-segregation of alloying elements and H favours grain boundary decohesion, and the strong partitioning of H into the second-phase particles removes solute H from the matrix, hence preventing H embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the role of H traps in minimizing cracking and guiding new alloy design. Atom-scale analysis of hydrogen and other elements at the grain boundaries of a 7xxx aluminium alloy shows that co-segregation of elements favours grain boundary decohesion, and that hydrogen embrittlement is prevented by strong partitioning into the second-phase particles.

Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used cryo-transfer atom probe tomography to observe hydrogen at specific microstructural features in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation for embrittlement models. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that these incoherent boundaries can act as trapping sites. This information is vital for designing embrittlement-resistant steels.

Material embrittlement is often encountered in machining, heat treatment, hydrogen and low-temperature conditions among which machining is strain-rate related. More strain-rate evoked embrittlement is expected in material loading processes, such as in high-speed machining and projectile penetration. In order to understand the fundamental mechanisms of the strain-rate evoked material embrittlement, this study is concerned with the material responses to loading at high strain-rates. It then explores the strain-rate evoked material embrittlement and fragmentation during high strain-rate loading processes and evaluates various empirical and physical models from different researchers for the assessment of the material embrittlement. The study proposes strain-rate sensitivity for the characterization of material embrittlement and the concept of the pseudo embrittlement for material responses to very high strain-rates. A discussion section is arranged to explore the underlying mechanisms of the strain-rate evoked material embrittlement and fragmentation based on dislocation kinetics.