Energetic and kinetic evaluations conducted in Cu-3.34 at % Sn through differential scanning calorimetry

Abstract

Microcalorimetric enthalpy measurements associated with the different peaks appearing during linear heating of Cu-3.34 at % Sn were made in a 50% cold-rolled alloy. Unlike the situation in the deformed material, quenched and furnace-cooled alloys do not exhibit thermal events at any of the heating rates employed in the temperature range scanned. In the cold-rolled condition, from the energetic and kinetic analysis of the first exothermic peak, designated Stage 1, and of the endothermic peak, designated Stage 3, it was consistently inferred that they correspond, respectively, to the growth on dislocations of a metastable phase e′ and to its subsequent dissolution prior to recrystallization. Such inference was also supported by Vickers microhardness and yield-stress determinations. The calculated volume fraction for e′ after Stage 2 goes to completion, is about 0.02. A suitable expression previously developed for enthalpy release due to the pinning of solute atoms to partial dislocations was applied to compute dislocation density from the exothermic peak (Stage 2). The calculated value is in excellent agreement with those obtained from the analysis of the recrystallization trace (Stage 4) and from tensile tests, thus confirming that the second DSC trace actually corresponds to the solute segregation process. It is also suggeseted that additional dislocation-induced formation of e′ might take place as a consequence of the enhanced solute concentration around partial dislocations. The non-isothermal dissolution kinetics of e′ was adequately described by an integrated kinetic model function essentially appropriate for application in one-dimensional diffusion situations.