Molecular-dynamics computer simulations of a model Ni nanocrystalline sample with mean grain size 12 nm under uniaxial tension is reported. The microscopic view grain-boundary sliding addressed. Two atomic processes are distinguished in the interfaces during sliding: shuffling and stress-assisted free-volume migration. activated accommodation high-stress room-temperature conditions triple-junction migration, dislocation activity.

Plastic deformation in coarse-grained metals is governed by dislocation-mediated processes. These processes lead to the accumulation of a residual dislocation network, producing inhomogeneous strain and an irreversible broadening Bragg peaks x-ray diffraction. We show that during plastic electrodeposited nanocrystalline nickel, peak reversible upon unloading; hence, process does not build up network. The results were obtained situ profile analysis using Swiss Light Source. This technique,...

We investigate the structure and mobility of single self-interstitial atom vacancy defects in body-centered-cubic transition metals forming groups 5B (vanadium, niobium, tantalum) 6B (chromium, molybdenum, tungsten) Periodic Table. Density-functional calculations show that all these axially symmetric ⟨111⟩ configuration has lowest formation energy. In chromium, difference between energies ⟨110⟩ configurations is very small, making two structures almost degenerate. Local densities states for...

The present work deals with the atomic mechanism responsible for emission of partial dislocations from grain boundaries (GB's) in nanocrystalline metals. It is shown that 12 and 20 nm size samples GB's containing GB can emit a dislocation during deformation by local shuffling stress-assisted free volume migration. often emitted or absorbed neighboring triple junction. further suggested degree delocalization surrounding boundary determines whether associate displacements into Burgers vector...

We develop a semi-empirical many-body interatomic potential suitable for large scale molecular dynamics simulations of magnetic α-iron. The functional form the embedding part is derived using combination Stoner and Ginzburg–Landau models. show that it symmetry broken solutions model describing spontaneous magnetization atoms provide link between magnetism forces. discuss range applications new method.

Tensile experiments of fully dense nanocrystalline structures with a mean grain size less than 100 nanometers demonstrate considerable increase in hardness but remarkable drop elongation-to-failure, indicating brittle behavior. However, dimple are often observed at the fracture surface, some type ductile mechanism. Guided by large-scale atomistic simulations, we propose that these result from local shear planes formed around clustered grains that, because their particular misorientation,...

Body-centered-cubic iron develops an elastic instability, driven by spin fluctuations, near the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ phase transition temperature ${T}_{c}=912\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ that is associated with dramatic reduction of shear stiffness constant ${c}^{\ensuremath{'}}=({c}_{11}\ensuremath{-}{c}_{12})/2$ ${T}_{c}$. This ${c}^{\ensuremath{'}}$ has a profound effect on dependence anisotropic self-energies dislocations in...

Large-scale molecular dynamics of cascade production the primary damage state are performed in fcc nanocrystalline Ni average grain diameters 5 and 12 nm. Primary knock-on atom kinetic energies 5-30 keV simulated. During thermal spike phase, significant atomic motion towards surrounding boundary structure is observed, characterized by many replacement-collision sequences. Upon resolidification, excess volume condenses to form vacancy dominated defects with a complex partial dislocation...

We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state ground state. On plotting vertex-type populations as function time, we can characterize relaxation, which occurs in two stages, namely string domain regime. Kinetic Monte Carlo simulations agree well temporal evolution magnetic when including disorder, experimental results be explained by...

Abstract Materials with interacting magnetic degrees of freedom display a rich variety behaviour that can lead to novel collective equilibrium and out-of-equilibrium phenomena. In equilibrium, thermodynamic phases appear the associated phase transitions providing characteristic signature underlying behaviour. Here we create thermally active artificial kagome spin ice is made up large array dipolar nanomagnets undergoes predicted by microscopic theory. We use low energy muon spectroscopy...

With a specific stimulus, shape-memory materials can assume temporary shape and subsequently recover their original shape, functionality that renders them relevant for applications in fields such as biomedicine, aerospace, wearable electronics. Shape-memory polymers composites is usually achieved by exploiting thermal transition to program the shape. This may be problematic heat-sensitive environments, when rapid uniform heating required. In this work, soft magnetic composite produced...

New generation nuclear fission and future fusion reactors provide one approach to address the world's increasing energy requirements. The irradiation of fission/fusion components can lead fundamental changes in material properties that affect stability performance not only component but entire reactor. How does state evolve with respect dose, there exist a microstructure resistant further irradiation? present work develops new computationally efficient answer these questions.

In the past two decades, numerous relaxation or physical aging experiments of metallic glasses have revealed signatures intermittent atomic-scale processes. Revealed via intensity cross-correlations from coherent scattering using x-ray photon correlation spectroscopy (XPCS), observed abrupt changes in time-domain atomic motion does not fit picture gradual slowing down times and their origin continues to remain unclear. Using a binary Lennard-Jones model glass subjected microsecond-long...

Crack propagation studies in nanocrystalline Ni samples with mean grain sizes ranging from 5 to 12 nm are reported using atomistic simulations. For all pure intergranular fracture is observed. Intergranular shown proceed by the coalescence of microvoids formed at boundaries ahead crack. The energy released during higher than Griffith value, indicating an additional grain-boundary accommodation mechanism.

Large scale molecular dynamics (MD) simulations are used to simulate the plastic deformation of a nanocrystalline model Ni sample with an average grain size 5 nm containing 125 grains at 800 K up 4.0% strain. For first time in MD simulation, emerging shear planes involving several boundaries have been observed indicating cooperative activity between grains. It is found that three mechanisms involved development such planes: grain-boundary migration, continuity plane via intragranular slip,...