Jc Van Duysen

Massively parallel molecular dynamics simulations with EAM potentials

Abstract Molecular dynamics of cascades in pure iron and iron–copper alloys using embedded atom method type of interatomic potentials are presented. Reliable simulations of radiation damage at the atomic scale with high energy Primary Knocked Atoms (PKA) need systems with large numbers of particles and very long computational time. To perform the simulation in a reasonable amount of time high-performance computer systems such as massively parallel machines need to be used. This paper presents the parallelisation strategy applied to a serial classical Molecular Dynamics code: DYMOKA. The original sequential Fortran code CDCMD from the University of Connecticut was first improved algorithmically by applying a link cell method for the neighbour list construction of the Verlet list, resulting in a fully linear algorithm. The parallelisation strategy adopted is a multidimensional domain decomposition of the simulation box using a link cell method and a Verlet list method for each subdomain independently. The p...

Influence of substrate roughness and lateral spacing on morphology and brittleness of different Cr-C PVD coatings

Abstract 10 μm thick, carbon doped (1.1wt.%) chromium coatings were deposited by non-reactive magnetron sputtering on steel substrates (XC18) with different surface preparations (electrolytic polishing, SiC grinding, shot peening) and by reactive magnetron sputtering on stainless steel substrates having a deliberately modified surface texture. For each substrate finish, surface topography before and after deposition is characterized by scanning stylus profilometry. Fractographs and X-ray diffraction diagrams show the influence of initial substrate surface morphology (roughness and lateral spacing) on coating growth mechanisms and microstructure. High-load Vickers indentation reveals that apparent intrinsic coating brittleness, computed from radial crack lengths, increases with perfection of coating microstructure which, in turn, decreases with increasing ratio of roughness over horizontal spacing, Rtm:Sm.

Computer simulations study of iron–copper alloy

Abstract The vessel steels of pressurised water reactors are embrittled by neutron irradiation. The changes of mechanical properties are commonly supposed to result from the formation of point defects, dislocation loops, voids and Cu-rich precipitates. The composition of such precipitates, specially the existence of vacancies, is not accessible through experiments. It is suggested that two mechanisms promote the formation of Cu-rich features in pressure vessel steels during neutron irradiation. When the Cu content is lower than 0.1%, solute-rich atmospheres can be formed in displacement cascades. For higher Cu contents, in addition to the latter phenomenon, a mechanism of accelerated precipitation can also induce the formation of Cu-rich clusters or precipitates. In order to understand all the mechanisms, Molecular Dynamics and Monte Carlo simulations have been carried out in pure Fe, and Fe–Cu alloys. Inter-atomic potentials of the Embedded Atom Method type, found in literature for pure Fe and pure Cu we...

Damage region formation in ferritic steels induced by light water reactor neutron spectrum

Abstract A new theoretical model for damage region formation is proposed. The model is based on numerical solution of the Boltzmann transport equation for knocked-on atoms. A key point of this model is the selfconsistent determination of subcascade overlapping energy E over (the threshold energy for distinguished damage region formation). Damage region density and size distributions in ferritic steels (Fe–0.2 wt% Cu and Fe–0.2 wt% Cu–0.3 wt% Si) under neutron irradiation in light water reactor spectrum were calculated.

The Relationship Between Microstructure and Mechanical Properties of a 9% Cr, 2% Mo, Nb, v Ferritic Steel

ABSTRACT The evolution of the mechanical properties of the ferritic-martensitic 9 % Cr -2 % Mo-Nb-V (EM12) steel during aging between 475 and 625°C and during creep at 500 and 550°C is explained in terms of the antagonistic effects of two related phenomena: the intragranular precipitation of a Mo-rich Fe-Cr-Mo intermetallic compound in the ferrite and the resulting Mo depletion of the solid solution.