Mechanistic origin of high retained strength in refractory BCC high entropy alloys up to 1900K

The body centered cubic (BCC) high entropy alloys MoNbTaW and MoNbTaVW show exceptional strength retention up to 1900K. The mechanistic origin of the retained strength is unknown yet is crucial for finding the best alloys across the immense space of BCC HEA compositions. Experiments on Nb-Mo, Fe-Si and Ti-Zr-Nb alloys report decreased mobility of edge dislocations, motivating a theory of strengthening of edge dislocations in BCC alloys. Unlike pure BCC metals and dilute alloys that are controlled by screw dislocation motion at low temperatures, the strength of BCC HEAs can be controlled by edge dislocations, and especially at high temperatures, due to the barriers created for edge glide through the random field of solutes. A parameter-free theory for edge motion in BCC alloys qualitatively and quantitatively captures the strength versus temperature for the MoNbTaW and MoNbTaVW alloys. A reduced analytic version of the theory then enables screening over >600,000 compositions in the Mo-Nb-Ta-V-W family, identifying promising new compositions with high retained strength and/or reduced mass density. Overall, the theory reveals an unexpected mechanism responsible for high temperature strength in BCC alloys and paves the way for theory-guided design of stronger high entropy alloys.Comment: This version corrects the theory and provides more extensive explanation

Modelling diffusion in crystals under high internal stress gradients

Diffusion of vacancies and impurities in metals is important in many processes occurring in structural materials. This diffusion often takes place in the presence of spatially rapidly varying stresses. Diffusion under stress is frequently modelled by local approximations to the vacancy formation and diffusion activation enthalpies which are linear in the stress, in order to account for its dependence on the local stress state and its gradient. Here, more accurate local approximations to the vacancy formation and diffusion activation enthalpies, and the simulation methods needed to implement them, are introduced. The accuracy of both these approximations and the linear approximations are assessed via comparison to full atomistic studies for the problem of vacancies around a Lomer dislocation in Aluminium. Results show that the local and linear approximations for the vacancy formation enthalpy and diffusion activation enthalpy are accurate to within 0.05 eV outside a radius of about 13 Å (local) and 17 Å (linear) from the centre of the dislocation core or, more generally, for a strain gradient of roughly up to 6 × 10^6 m^-1 and 3 × 10^6 m^-1, respectively. These results provide a basis for the development of multiscale models of diffusion under highly non-uniform stress

Orchestral Theatre and the Concert as a Performance Laboratory

This is the author accepted manuscript. The final version is available from Cambridge University Press via the DOI in this recordIn the last decade the National Theatre has presented two productions featuring an onstage orchestra (the Southbank Sinfonia) that has been choreographed and made into a key part of the spectacle: Every Good Boy Deserves Favour, by Tom Stoppard with a musical score by André Previn, performed in 2009 and 2010, and Peter Shaffer’s Amadeus, performed in 2016 and 2018. Contemporaneously, a vanguard of British orchestras has begun to explore how concerts can be presented in ways that are more theatrically sophisticated than the standard concert format. This article investigates ‘orchestral theatre’ as an aesthetic proposition by examining the collaborations between the Southbank Sinfonia and the National Theatre, and their legacy in a series of experimental concerts staged by the Southbank Sinfonia entitled #ConcertLab, which began in 2017. The article aims to identify the artistic and cultural significance of the aforementioned collaborations and #ConcertLab so as to better understand contemporary efforts to present orchestras (and, more broadly, classical music) in a theatrically innovative manner.Arts and Humanities Research Council (AHRC

Ab initio Modelling of the Early Stages of Precipitation in Al-6000 Alloys

Age hardening induced by the formation of (semi)-coherent precipitate phases is crucial for the processing and final properties of the widely used Al-6000 alloys. Early stages of precipitation are particularly important from the fundamental and technological side, but are still far from being fully understood. Here, an analysis of the energetics of nanometric precipitates of the meta-stable $\beta''$ phases is performed, identifying the bulk, elastic strain and interface energies that contribute to the stability of a nucleating cluster. Results show that needle-shape precipitates are unstable to growth even at the smallest size $\beta''$ formula unit, i.e. there is no energy barrier to growth. The small differences between different compositions points toward the need for the study of possible precipitate/matrix interface reconstruction. A classical semi-quantitative nucleation theory approach including elastic strain energy captures the trends in precipitate energy versus size and composition. This validates the use of mesoscale models to assess stability and interactions of precipitates. Studies of smaller 3d clusters also show stability relative to the solid solution state, indicating that the early stages of precipitation may be diffusion-limited. Overall, these results demonstrate the important interplay among composition-dependent bulk, interface, and elastic strain energies in determining nanoscale precipitate stability and growth

Population Growth and Other Statistics of Middle-sized Irish Towns. General Research Series Paper No. 85, April 1976

The basic aim of the study is the presentation of tables of comparative statistical data relating to 97 towns with population 5OO-1O,OOO in 1971 and analyses of such data. The exclusion of the four County Boroughs and Dun Laoghaire together with twelve other large towns and all small towns and villages, was to impart a degree of homogeneity to the inquiry, as regards function of town. The 97 towns range from Mullingar, the largest with a population of 9,245 to Cootehill with 1,542

Predicting hydrogen embrittlement in steels and high entropy alloys

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Family and land in the West of Ireland

[From the introduction]: This thesis is about families and land in the West of Ireland. More precisely, treating land as a basic resource, it examines the social relationships which spring up around it; how land is acquired, utilized, valued, competed for, hoarded, bought and sold are central issues in the thesis. These issues are explored against the background of a small rural community in South Mayo. The thesis is an ethnographic statement, a picture of people in action at one point in time. It is not a 'community study', but it uses a community as a setting or location for the exploration of problems of wider relevance. While the concepts used are drawn largely from sociology and social anthropology, the thesis straddles several academic fences into the domains of the economist, the social historian and the geographer

Fermi Liquids and the Luttinger Integral

The Luttinger Theorem, which relates the electron density to the volume of the Fermi surface in an itinerant electron system, is taken to be one of the essential features of a Fermi liquid. The microscopic derivation of this result depends on the vanishing of a certain integral, the Luttinger integral $I_{\rm L}$, which is also the basis of the Friedel sum rule for impurity models, relating the impurity occupation number to the scattering phase shift of the conduction electrons. It is known that non-zero values of $I_{\rm L}$ with $I_{\rm L}=\pm\pi/2$, occur in impurity models in phases with non-analytic low energy scattering, classified as singular Fermi liquids. Here we show the same values, $I_{\rm L}=\pm\pi/2$, occur in an impurity model in phases with regular low energy Fermi liquid behavior. Consequently the Luttinger integral can be taken to characterize these phases, and the quantum critical points separating them interpreted as topological.Comment: 5 pages 7 figure

Weighted-density approximation for general nonuniform fluid mixtures

In order to construct a general density-functional theory for nonuniform fluid mixtures, we propose an extension to multicomponent systems of the weighted-density approximation (WDA) of Curtin and Ashcroft [Phys. Rev. A 32, 2909 (1985)]. This extension corrects a deficiency in a similar extension proposed earlier by Denton and Ashcroft [Phys. Rev. A 42, 7312 (1990)], in that that functional cannot be applied to the multi-component nonuniform fluid systems with spatially varying composition, such as solid-fluid interfaces. As a test of the accuracy of our new functional, we apply it to the calculation of the freezing phase diagram of a binary hard-sphere fluid, and compare the results to simulation and the Denton-Ashcroft extension.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E as Brief Repor