Untangling competition between epitaxial strain and growth stress through examination of variations in local oxidation

Understanding corrosion mechanisms is of importance for reducing the global cost of corrosion. While the properties of engineering components are considered at a macroscopic scale, corrosion occurs at micro or nano scale and is influenced by local microstructural variations inherent to engineering alloys. However, studying such complex microstructures that involve multiple length scales requires a multitude of advanced experimental procedures. Here, we present a method using correlated electron microscopy techniques over a range of length scales, combined with crystallographic modelling, to provide understanding of the competing mechanisms that control the waterside corrosion of zirconium alloys. We present evidence for a competition between epitaxial strain and growth stress, which depends on the orientation of the substrate leading to local variations in oxide microstructure and thus protectiveness. This leads to the possibility of tailoring substrate crystallographic textures to promote stress driven, well-oriented protective oxides, and so to improving corrosion performance

In-situ TEM characterization and atomistic simulation of cavity generation and interaction in tungsten at 800 °C under dual W²⁺/He⁺ irradiation

In this work, we have investigated the role of pre-existing nano-scale cavities and irradiation sequence in helium clustering, and in the evolution of the cavity population in tungsten at 800 °C, by performing in-situ Transmission Electron Microscopy (TEM) characterizations under dual-beam W2+(600 keV)/He+(10 keV) irradiation to a total dose of 0.351 dpa, and supported by molecular simulations. Pre-existing cavities, induced by single W2+ irradiation to 0.256 dpa, were seen attract induced defects from subsequent irradiations, resulting in enhanced cavity size and a reduced number density in sequential irradiation when compared to concurrent irradiation. Such cavities developed faceted geometries and saturated in number density at an additional 0.051 dpa induced by He+ exposure in the sequential irradiation. In contrast, concurrent irradiations generate a denser cavity distribution that showed no sign of saturation or faceting up to the total irradiation damage of 0.351 dpa. In addition, Molecular Dynamics and Statics simulations were performed using LAMMPS software. These showed the pre-existing cavities to be trapping sites for helium atoms. Despite the large binding energy of ∼6 eV of those cavities, He-He interactions still occurred beyond the effective radius of such sinks, leading to additional He-He clustering not seeded by neighbouring cavities. These results point to the importance of selecting the irradiation conditions to simulate synergistic ion effects on cavity formation and evolution in plasma-facing tungsten-base materials

Damage in Zircaloy-2 secondary phase particle compositions from proton and neutron irradiation

The neutron files are the output from the program SPECTRA-PKA, containing the product atoms, recoil rates and displacement per atoms calculated for a thermal neutron spectrum interacting with pure Zr, Zr2(Fe,Ni) and Zr(Fe,Cr)2. The proton files are the output from the program SRIM for 2MeV protons interacting with pure Zr, Zr2(Fe,Ni) and Zr(Fe,Cr)2 using the Kinchin-Pease (kp) and full cascade (fc) calculation option available in SRIM. Using equation (1) from the paper 'Modelling the interaction of primary irradiation damage and precipitates: implications for experimental irradiation of zirconium alloys', the number of vacancies can be converted into displacements per atom

Data for: The effect of irradiation temperature on damage structures in proton-irradiated zirconium alloys

These data files were used in the analysis of 2.3 dpa Zircaloy-2 and Low-Sn ZIRLO samples, irradiated at various temperatures

The phenotypic spectrum of Schaaf-Yang syndrome: 18 new affected individuals from 14 families

Genetics of disease, diagnosis and treatmen

Modelling non-adiabatic processes using correlated electron-ion dynamics

Here we survey the theory and applications of a family of methods (correlated electron-ion dynamics, or CEID) that can be applied to a diverse range of problems involving the non-adiabatic exchange of energy between electrons and nuclei. The simplest method, which is a paradigm for the others, is Ehrenfest Dynamics. This is applied to radiation damage in metals and the evolution of excited states in conjugated polymers. It is unable to reproduce the correct heating of nuclei by current carrying electrons, so we introduce a moment expansion that allows us to restore the spontaneous emission of phonons. Because of the widespread use of Non-Equilibrium Green's Functions for computing electric currents in nanoscale systems, we present a comparison of this formalism with that of CEID with open boundaries. When there is strong coupling between electrons and nuclei, the moment expansion does not converge. We thus conclude with a reworking of the CEID formalism that converges systematically and in a stable manner. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010