Effects of cold rolling on the precipitation kinetics and the morphology evolution of intermediate phases in Inconel 718 alloy

Abstract

Isochronal DSC measurements of various degrees cold-rolled Inconel 718 alloy samples were implemented to investigate the effect of cold rolling on the precipitation kinetics of intermediate phases in Inconel 718 alloy. The result shows that the values of the onset temperature ( TOnset1), the peak temperature (TPeak1) and the end temperature (TEnd1) of γ″-phase precipitation decrease as the degree of cold rolling increases. In contrast, all values of the onset temperature (TOnset2), the peak temperature (TPeak2) and the end temperature (TEnd2) of δ-phase precipitation first increase and then decrease with the degree of cold rolling increasing as a consequence of a combined effect of lack of Nb atoms and recrystallization. Two sets of isothermal aging experiments were also carried out to study the effect of cold rolling on the morphology evolution of γ″-phase and δ-phase in Inconel 718 alloy. It is found that cold rolling promotes γ″→δ transformation and the morphology of γ″-phase turns more globular as the degree of cold rolling increases for the cold-rolled Inconel 718 alloy samples with isothermal aging at 800 °C for 8 h (procedure A). Moreover, for the cold-rolled Inconel 718 alloy samples with isothermal aging at 950 °C for 6 h (procedure B), cold rolling facilitates δ-phase precipitation and the δ-phase particles gradually sphericalized with increase in the degree of cold rolling.