Abstract
Internal friction has been measured at elevated temperatures to study the diffusion of C atoms in low carbon Fe-Al-C alloys containing 0.002∼5.28 wt%Al. It is observed that the Snoek peak proper to the Fe-C binary alloys is broadened and reduced in height with increasing of the Al content. Besides, the addition of Al produces another peak at the higher temperature, and the peak increases in height at the expense of the Snoek peak. The activation energies of the Snoek peak and the second peak are 18.5∼19.5 kcal/mol and 23.6∼24.5 kcal/mol, respectively. Though the Snoek peak in pure Fe-C alloy is somewhat greater in width than that calcuated as having the single relaxation time, the Snoek peak in the Fe-Al-C alloys are still larger in width than that of the binary alloy and the second peak is much greater in width. The broadening can be explained by allowing their relaxation times to have an appropriate error-functional distribution. By selecting suitable values of parameters, the calculated curves are fitted very well to the observed ones.
From the obtained results, it is suggested that the Snoek peak is due to the stress-induced diffusion of C atoms at Fe-Fe interstices expanded by the addition of Al, and the second peak is due to that at Fe-Al interstices. The Fe-Al interstices are considered as if they were under a compressed condition, as contrasted with the Fe-Fe interstices.
