The recovery of internal friction in an iron-carbon alloy

Publisher Website
Google Scholar
Abstract
Strain ageing following plastic deformation was studied at the flow stress and at zero stress levels over the temperature range -37° to 24°C in annealed (at 870°C) and in quenched (from 700°C) polycrystalline and in annealed (at 870°C) single crystal specimens of Ferrovac-E iron. The interactions of interstitial carbon and nitrogen with dislocations were derived from the time-dependent changes in the dislocation damping component of the attenuation at 5 MHz frequency, i.e. from the recovery of internal friction. Two stages of strain ageing observed correspond to Snoek rearrangement and to Cottrell atmosphere formation. The activation energy for Snoek rearrangement was found to be 14·8 ± 0·5 kcal/mole by applying the Granato-Hikata-Lücke equation and 14·0 ± 2·3 kcal/mole by the Arrhenius relationship, with an ageing time exponent of 2/3. The activation energy for the second stage was 22·0 ± 2·0 kcal/mole with the ageing time exponent between 1/3 and 1/2. The ageing stress levels, flow stress or zero stress, do not seem to have any effect on either activation energy or kinetics. Mechanical properties associated with strain ageing are, however, a function of the ageing stress levels and this has led some investigators to an erroneous assumption of stress-assisted diffusion of interstitials.