Abstract
This work presents a comprehensive and detailed ab initio study of interactions between the tilt Σ5(210) grain boundary (GB), impurities X (X = Al, Si) and vacancies (Va) in ferromagnetic fcc nickel. To obtain reliable results, two methods of structure relaxation were employed: the automatic full relaxation and the finding of the minimum energy with respect to the lattice dimensions perpendicular to the GB plane and positions of atoms. Both methods provide comparable results. The analyses of the following phenomena are provided: the influence of the lattice defects on structural properties of material such as lattice parameters, the volume per atom, interlayer distances and atomic positions; the energies of formation of particular structures with respect to the standard element reference states; the stabilization/destabilization effects of impurities (in substitutional (s) as well as in tetragonal (iT) and octahedral (iO) interstitial positions) and of vacancies in both the bulk material and material with GBs; a possibility of recombination of Si(i)+Va defect to Si(s) one with respect to the Va position; the total energy of formation of GB and Va; the binding energies between the lattice defects and their combinations; impurity segregation energies and the effect of Va on them; magnetic characteristics in the presence of impurities, vacancies and GBs. As there is very little experimental information on the interaction between impurities, vacancies and GBs in fcc nickel, most of the present results are theoretical predictions, which may motivate future experimental work.
Highlights
Various crystal defects such as impurities, vacancies (Va) and grain boundaries (GB) significantly affect material properties and are objects of both theoretical and applied research
We present an ab initio study of the tilt Σ5(210) grain boundary in ferromagnetic fcc nickel both in the clean state and with segregated Al and Si impurities accompanied by vacancies
We look for the preferred positions of impurities at the GB and analyze their effect on atomic arrangement and magnetism
Summary
Various crystal defects such as impurities, vacancies (Va) and grain boundaries (GB) significantly affect material properties and are objects of both theoretical and applied research. Recent investigations deal with topics such as energetics of GB formation and its sensitivity to segregated impurities playing the role of either embrittlers or cohesion enhancers [1,2,3]. These issues have far-reaching practical implications manifested in the mechanical and magnetic properties. Let us mention the strengthening/embrittling energy of segregated sp-elements from the 3rd, 4th and 5th period at the Σ5(210) grain boundary in ferromagnetic fcc nickel and cobalt [2,3,4,5,6,7,8]. Recent trends and open problems in grain boundary segregation are discussed in the reviews [3,12]
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