Internal friction, dilatometric and calorimetric study of anelasticity in Fe–13 at.% Ga and Fe–8 at.% Al–3 at.% Ga alloys

Abstract

This paper investigates the structural transitions associated with different cooling rates from a high temperature disordered state and the effect of substitution of Ga atoms by Al atoms in Fe–Ga binary alloys on the ordering processes. Two iron-based low carbon (about 0.04 at.% C) alloys Fe–13 at.% Ga and Fe–8 at.% Al–3 at.% Ga are studied. Internal friction, dilatometric and calorimetric tests are carried out to check ordering in these alloys and contribution of structural defects to relaxation spectrum. Several thermally activated internal friction peaks have been observed and their activation parameters evaluated by means of temperature and frequency dependent internal friction tests using forced vibration. For most of these peaks physical mechanisms are proposed. Apart from these thermally activated relaxation peaks, a structural, frequency independent relaxation takes place at 250–300 °C. Dilatometric and DSC curves show the appearance of a contraction effect in the same temperature range. This effect was studied in alloys cooled down with different cooling rates. We believe that the frequency independent internal friction peak (denoted as the P3 peak in this paper) and peaks at dilatometric and DSC curves are controlled by the same structural mechanism and therefore the activation energy for this anelastic mechanism is derived from DSC data.