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Graphical abstract Flow stress of multiple twinned nanocrystalline aluminium decreases with deducing grain size and shows an inverse Hall-Petch relationship. Abstract The mechanical behaviour of rapidly solidified aluminium with multiple twinned nanograins is investigated by a large-scale molecular dynamics simulation. The nanocrystalline structures with mean grain sizes ranging from 3.1 nm to 24.4 nm are prepared by quenching liquid at appropriate cooling rates. It is found that the mechanical properties of rapidly solidified aluminium with multiple twinned nanograins are dependent on its grain size. The flow stress displays inverse Hall-Petch relationship in the present grain-size range. The multiple twinned nanocrystalline aluminium with large and small grain sizes respectively displays different deformation mechanisms during the uniaxial tensile processes. For that with large grain size, the dominated deformation mechanism is twin boundary migration, though co-existing with dislocation activities. And the morphologies of multiple twinned nanograins remain nearly unchanged during the deformation process. For that with small grain size, the deformation is governed by the softening mechanisms of grain growth and detwinning. The grain boundary migration and grain rotation are found in the grain growth process. And the morphologies of multiple twinned nanograins gradually transform into parallel twins or monocrystal. [ABSTRACT FROM AUTHOR]

• The interactions between Re and Σ5(130) grain boundary in W have been systematically investigated. • GBs are sinks for Re atoms through interstitial or vacancy assisted mechanisms. • Re atoms are more likely to locate at substitutional sites nearby the GB in kinetic segregation process. • Re clusters have strong effect on impeding the plastic deformation of the GBs, and may cause the embrittlement of materials. High energy neutron irradiation not only causes the transmutation of tungsten (W), but also induces transmutation elements to segregate and precipitate at grain boundaries. In this work, the segregation of transmutation-produced rhenium (Re) and their clusters at a Σ5(130) grain boundary (GB) in bulk W has been investigated by using both molecular dynamics and molecular statics methods. It is found that, for single interstitial, Re atom diffuses from the bulk to the GB region via a three-dimensional rotation and migration in the form of an interstitial 〈1 1 1〉 Re-W mixed dumbbell, because the rotation and migration barriers of a Re-W dumbbell are both small. When Re atoms are absorbed by the GB, it is noteworthy that Re atoms tend to occupy the substitutional sites near the GB. The segregation energy of interstitial Re is ranged from −7.67 to −6.12 eV, and the effective interaction distance between the GB and Re interstitials is about 7 Å, which increases with increasing the cluster size. By modeling the uniaxial tensile test of W-GB structure containing Re substitution clusters, the fracture strength and elongation of the GB are significantly reduced. The present results provide important insights into the detailed mechanisms of Re segregation at GBs and its possible effects on the mechanical properties of W-based materials. [ABSTRACT FROM AUTHOR]

• New interatomic potentials of Ta-Ta and W-Ta based on F-S formalism have been developed. • The formation energies of point defects and the non-degenerate core structure of a 1/2 〈1 1 1〉 screw dislocation in Ta bulk are well reproduced. • The developed potentials have high accuracy and good transferbility. • These potentials are applicable for describing the evolution of point defects in Ta and W-Ta alloys. Tungsten (W) and W-based alloys are regarded as the most promising candidates for plasma facing materials (PFMs) in future fusion reactors. In this work, new interatomic potentials for Ta element and W-Ta alloy have been developed based on the Finnis-Sinclair formalism, in combination with our previously developed potential for W. The potential parameters for Ta were determined by fitting to a set of experimental and first-principles data, including lattice constant, cohesive energy, elastic constants, point defects formation energies and Rose's equation of state for the bcc lattice. The W-Ta cross parameters were fitted to the first-principles data of the formation energies and binding energies of Ta atom with different point defects in bulk W. The present potentials not only reproduce some important physical properties of various point defects, but also predict the non-degenerate/compact core structure of the 1/2 〈1 1 1〉 screw dislocation in bulk Ta, which is the same as DFT calculations. The developed potentials were expected to be suitable for atomistic simulations of point defects evolution in Ta and W-Ta binary alloys. [ABSTRACT FROM AUTHOR]