Effect of substitutional ordering on the carbon Snoek relaxation in Fe-Al-C alloys

It is shown that the alloying of iron by Al (0 to 30 at%) shifts the carbon Snoek peak to a higher temperature and broadens it in the disordered state (quenched samples). Ageing of quenched samples with 19.6 at% Al shifts the peak to lower temperatures and makes it more narrow due to substitutional ordering of the DO3-type. The explanation of concentration dependence of internal friction and influence of ordering is done on the basis of computer simulation of energy distribution for carbon atoms in solid solution due to its interaction with Al atoms and changing of this distribution due to Al ordering. The model of the long-range strain-induced (elastic) C-Al interaction supplemented by the short-range "chemical" interaction is successfully used. The change of the calculated peak temperature and its width is in good agreement with experimental data. It is shown that the main factor which determines the effect of Al on the carbon Snoek peak in iron is the long-range elastic interaction.