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

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 gamma ' precipitate size, volume fraction and distribution on gamma ' 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 degrees C (10 min soaking) at rates of 3000 degrees C/min and 2.5 degrees 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 gamma ' precipitates. The activation energies for gamma ' precipitation and dissolution under different conditions were determined from the Kissinger equation. The small, monomodal precipitate size distribution sample (3000 degrees C/min) exhibited lower activation energy during dissolution than one with a larger, monomodal (2.5 degrees 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.