DSC investigation of size-dependent γ′ dissolution and re-precipitation kinetics in Ni-based superalloy IN738LC

Abstract

ABSTRACT The novelty of the work is related to confirming using DSC of previous study by the authors, the determining dependency of the gamma prime dissolution in a Ni-based superalloy on precipitate size. In the present work, the effect of γ′ precipitate size, volume fraction and distribution on γ′ precipitate dissolution and re-precipitation behaviour in polycrystalline IN738LC alloy were investigated. The alloy was subjected to different heat treatments including standard ageing and cooling from 1200°C (10 min soaking) at rates of 3000°C/min and 2.5°C/min. The DSC results of these samples were used to calculate the activation energies and kinetics for the dissolution and re-precipitation of the γ′ precipitates. The activation energies for γ′ precipitation and dissolution under different conditions were determined from the Kissinger equation. The small, monomodal precipitate size distribution sample (3000°C/min) exhibited lower activation energy during dissolution than one with a larger, monomodal (2.5°C/min) and bimodal precipitate size (standard aged) distribution samples. Therefore, it is concluded that precipitate size has a direct influence on eventual precipitate kinetics, both in terms of dissolution and re-precipitation under service conditions.