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The commercialization of nanocrystalline metals and alloys is currently entering a renaissance period. Many of the processing and consolidation challenges that have haunted them are now more fully understood, opening the doors for stabilized nanocrystalline metals to be produced on a bulk scale. While challenges remain, the increased volume at which these materials are being supplied is for the first time allowing for investigations into more traditional methods of metal working, such as extruding, rolling, forming, and forging. Recently, the manufacturing science has been developed to allow nanocrystalline Cu-Ta alloys to progress to this point. This article therefore builds upon the last decade of evolutionary progression within the family of stabilized nanocrystalline Cu-Ta alloys by presenting some of the first findings related to scaled powder synthesis, production of billets, thin sheets, and foils. The mechanical performance and physical properties relevant to forming electrical contacts and pins including, tensile, J-integral fracture toughness, Charpy Impact, bi-axial tension, and conductivity are reported. This introductory investigation into forming such a novel material, provides evidence to these alloys potential at bridging the gap between being a scientific curiosity to that of a real engineering material. • The commercialization of nanocrystalline metals and alloys is currently entering a renaissance period. Many of the processing and consolidation challenges that have haunted them are now more fully understood, opening the doors for stabilized nanocrystalline metals to be produced on a bulk scale. While challenges remain, the increased volume at which these materials are being supplied, is for the first time allowing for investigations into more traditional methods of metal working, such as extruding, rolling, forming and forging. Recently, the manufacturing science has been developed to allow nanocrystalline Cu-Ta alloys, to progress to this point. This article therefore builds upon the last decade of progression within the family of stabilized nanocrystalline Cu-Ta alloys by presenting some of the first findings related to scaled powder synthesis, production of billets, thin sheets and foils. The mechanical performance and physical properties relevant to forming electrical contacts and pins including, tensile, J-integral fracture toughness, Charpy Impact, bi-axial tension, and conductivity are reported. This introductory investigation into forming such a novel material, provides evidence to these alloys potential at bridging the gap between being a scientific curiosity to that of a real engineering material. [ABSTRACT FROM AUTHOR]

Abstract: The ultrafine scale microstructure of three MA/ODS ferritic alloys (12YWT, 14YWT and MA957) have been characterized by atom probe tomography in the as-received condition and after isothermal heat treatments at temperatures of up to 24h at 1300°C (∼85% T m). Atom probe tomography revealed the presence of a high number density of 2–4nm diameter titanium-, yttrium- and oxygen-enriched particles. These ultrafine particles were found to be extremely resistant to coarsening during isothermal aging at 1300°C. Solute segregation of the alloying elements to dislocations and grain boundaries was also observed. [Copyright &y& Elsevier]

Abstract: An extensive experimental study characterizing the sequence of events that lead to the formation of a very high density of Y–Ti–O solute nanoclusters (NC) in mechanically alloyed, hot isostatically pressed ferritic stainless steels is reported. Yttria dissolves in the Fe–14Cr–3W(0.4Ti) powders during mechanical alloying. The dissolved Y and O, and when present Ti, subsequently precipitate during hot consolidation. The number densities and volume fractions of the NC decrease, and their radii increase, with increasing consolidation temperature. The NC form at 850 and 1000°C in milled alloys containing Y, both with and without Ti additions. The presence of Ti refines the NC, and both Ti and high milling energy are necessary for the formation of NC at the highest consolidation temperatures of 1150°C. However, the precise structure and composition of the NC are not well understood. Indeed, their character varies, depending on the alloy composition and processing variables. [Copyright &y& Elsevier]

Abstract Nanostructured ferritic alloys (NFAs) having sub-micron grain size with a high density of nano-oxides (NOs) (size of ∼2–3 nm) are one of the best candidates for structural components in Generation IV nuclear systems. In this study, 14YWT NFA cladding tubes were irradiated in BOR60 reactor up to 7 dpa at 360–370 °C. Detailed microstructural analysis has been conducted using bright field transmission electron microscopy, bright field scanning transmission electron microscopy, energy filtered transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and transmission Kikuchi diffraction techniques. This revealed cavities, <100> and <111> type dislocation loops, and α′ precipitates forming after irradiation with relationships between cavities and NOs, and α′ precipitates and NOs. Cavities mostly form on the NOs; whereas, α′ precipitates form between the NOs where the point defect concentration is high. Moreover, α′ precipitates are distributed homogenously on and around the dislocation loops which is consistent with the observation that there is no Cr segregation on dislocation loops. Grain boundaries were found to be mostly depleted in Cr; however, the characteristics of each grain boundary determines the Cr behavior and the α′ denuded zone around the grain boundaries. Mechanical properties of the irradiated tubes have been determined by using both low force and high force nanoindentation techniques, resulting in 1.03 ± 0.33 GPa and 0.82 ± 0.20 GPa hardening, respectively. Dispersed barrier hardening calculations and nanoindentation measurements are in good agreement. In this study, 14YWT NFA has been systematically studied after neutron irradiation to better understand its superior performance: low α′ concentration, low swelling and low radiation-induced hardening. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Cr-stabilized nanostructured ferritic alloys (NFAs), dispersion strengthened by an ultra-high density of nanooxides, are attractive candidates for many nuclear energy applications due to their high-temperature strength, in-service stability and remarkable irradiation tolerance. However, typical NFA deformation processing paths lead to crystallographic texturing, formation of brittle microstructures and low toughness orientations, making fabricating components very difficult. Here, we characterize the dislocation-mediated deformation mechanisms that lead to the brittle texture component. The as-extruded bar is less brittle than the cross-rolled plate, which contains a large population of pre-existing cleavage microcracks. More generally, deformed ODS/NFAs are most often textured and have anisotropic low toughness orientations, even absent microcracks. However, cross-rolling produces a very high volume fraction of a plate normal {001}<110>-texture component, which constitutes the brittle cleavage system in iron. Microcracks propagate along {001} low angle deformation induced subgrain boundaries in <110> directions after nucleating by the Cottrell mechanism. [ABSTRACT FROM AUTHOR]

Abstract: A present topic of high interest in magnetic fusion is the “gap” between near-term and long-term concepts for high heat flux components (HHFC), and in particular for divertors. This paper focuses on this issue with the aim of characterizing the international status of current HHFC design concepts for ITER and describing the different technologies needed in the designs being developed for fusion power plants. Critical material and physics aspects are highlighted while evaluating the current readiness level of long-term concepts, identifying the design and R&D gaps, and discussing ways to bridge them. [Copyright &y& Elsevier]