On the prediction of the yield stress of unimodal and multimodal γ′ Nickel-base superalloys

A new model for the yield stress in superalloys accounting for unimodal and multimodal gamma' size distributions is presented. A critique of the classic models on shearing is presented and important features not previously considered are incorporated in our model. This is extended to account for multimodal particle size distribution effects by weighting the individual particle contribution to the total strength. This analysis is focused on powder metallurgy alloys. The yield stress and particle strengthening are predicted for eight superalloys containing wide variations in initial microstructure, composition and at temperatures up to 700 degrees C. We demonstrate through a theoretical approach that the strength of alloys with multimodal gamma' is lower than those with unimodal gamma' radius in the vicinity of 10-30 nm. For the first time, a parameter-free physics-based model is able to predict the yield stress in superalloys with complex microstructures, including unimodal and multimodal gamma' size. This has been possible by removing limitations inherent to the classical models. Such approach also enables critical evaluation of the relevant factors contributing to the yield strength of polycrystalline superalloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.