On the correlation between electron structure and short range atomic orderin iron-based alloys

The experimental data on the concentration of free electrons in fee iron-ba sed alloys, results of theoretical calculations on the electronic structure and experimental data of atomic distribution are analysed. The electron st ructure of iron-based substitutional solid solutions and CrNi austenitic st eels alloyed by Mn, Mo, Cu, Si, Al and C, N was studied by means of the mea surement of conduction electron spin resonance. The electron exchange in bi nary fee Fe-N and Fe-C alloys was also calculated using an ab initio norm-c onserving pseudopotential method. It is shown that Ni, Cu, Si and Al increa se the concentration of free electrons, whereas Cr, Mn and Mo decrease it. Theoretical calculations as well as experimental data show that nitrogen in fee iron and iron-based solid solutions increases the state density at the Fermi surface, whereas carbon contributes its electrons to the states belo w the Fermi surface. Mossbauer spectroscopy was used to study the distribut ion of carbon and nitrogen in binary fee Fe-C and Fe-N alloys, while the da ta on the distribution of d-solutes in multicomponent solid solutions were obtained from the analysis of the contributions of different electronic sub systems, namely free electrons, isolated localized d-electrons (single solu te d-atoms) and superparamagnetic clusters (clusters of d-atoms), to the te mperature dependence of the magnetic susceptibility. The results of studies concerning the atomic distribution are consistent with the available data on the short range order in iron-based alloys. The following correlation is found: an increase in the concentration of free electrons assists the shor t range atomic ordering in iron-based alloys, whereas the localization of e lectrons promotes clustering of solute atoms. The state of atomic order inf luences properties like austenite stability, corrosion resistance and stren gth. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.