Dependence of vacancy-solute interactions on magnetic state in dilute iron-based alloys Oleg I. Gorbatov 1,a , Pavel A. Korzhavyi 2,b , Andrei V. Ruban 2,c , Yuri N. Gornostyrev 1,3,d 1 Institute of Quantum Materials Science, Ekaterinburg 620107, Russia 2 Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden 3 Institute of Metal Physics, Ural Division RAS, Ekaterinburg 620041, Russia a oleg.gorbatov@iqms.ru, b pavel@mse.kth.se, c a.v.ruban@gmail.com, d yug@imp.uran.ru Key words: magnetism, defects, diffusion, vacancy-solute interactions. Iron based alloys Abstract. Vacancy-solute interactions play a crucial role in diffusion-controlled phase transformations, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. The knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) under irradiation, as well as for advancing our general understanding of kinetic processes in alloys. Using first- principles calculations based on density functional theory and employing the locally self-consistent Green’s function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Ti – Cu), and 4d (Nb – Ag) elements. Interactions within the first two coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a very strong effect on the vacancy-solute interactions. Introduction Studies of interactions between vacancies and solute atoms (alloying elements or impurities) in crystalline materials are motivated by the significance of such interactions for our understanding of many important physical phenomena (such as diffusion, ordering, or decomposition) which occur in the materials during ageing or due to irradiation. Knowledge of vacancy-solute interactions is crucial for uncovering the atomistic mechanisms of thermal diffusion and, ultimately, of all the diffusion-controlled processes in alloys. Interactions of impurity atoms with vacancies are also of paramount importance for the development of atomistic models of production, migration, and especially agglomeration of radiation-induced defects. Iron-based alloys are undoubtedly the most important construction materials of our industrial society. Steels have been used as nuclear materials, for example, for making pressure vessels of fission reactors. Ferritic-martensitic steels (whose matrix has the body-centered-cubic lattice of α- Fe) have been found to be extremely tolerant to strong neutron irradiation [1]; therefore they are considered as promising construction materials for the next-generation fission reactors as well as for the future fusion reactors. Irradiation-enhanced diffusion and accompanying effects such as segregation or precipitation of insoluble impurities (e.g., Cu impurities in α-Fe) may strongly affect the mechanical properties of ferritic steels intended for the abovementioned nuclear energy applications. As follows from recent ab initio calculations [2], the vacancy-solute (vac-Cu) interactions in the first and the second coordination shells are the strongest point-defect interactions in the dilute solid solutions of Cu in α-Fe (the vac-Cu interactions are found to be even stronger than the Cu-Cu impurity interactions by which the precipitation of copper is driven). Atomistic modeling studies [3] show that the strong binding of vacancies to copper impurities and their clusters in the iron matrix has profound effects on the impurity diffusion. Therefore, the knowledge of vacancy-impurity interactions in ferritic steels is of great practical value as it enables for modeling the structure evolution and for predicting the mechanical behavior of these materials under irradiation. Solid State Phenomena, Vols. 172-174 (2011) pp 979-984 Online available since 2011/Jun/30 at www.scientific.net © (2011) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/SSP.172-174.979 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 109.187.127.126-01/07/11,12:48:22)