Modelling the High-Temperature Strengthening of Ni-Based Superalloys With Cuboidal γ’-Phase Particles

Abstract

The development of advanced Ni-based superalloys for gas turbine applications is strongly reliant on alloy strength design and optimisation through microstructure control. Herein, a new model of precipitation strengthening in Ni-based superalloys with large amounts of cuboidal γ’ particles is proposed and directly validated using commercial alloy (Alloy720Li)-based single-crystal tie-line model alloys with specially designed γ’ particle sizes and volume fractions. All factors responsible for Ni-based superalloy strengthening, including the γ/γ’ mixture, particle strengthening, and solid solution strengthening are extracted from the compressive stress-strain curves performed over a wide temperature range. The strength increment due to particle strengthening is predicted for five model alloys with various γ’-particle volume fractions, sizes, and shapes. The pair-coupling model assuming the presence of cuboidal γ’ particles accurately predicts alloy strength over a wide temperature range (up to 760 °C) for volume fractions of >45%, whereas the classical model assuming spherical γ’ particles is valid only for volume fractions of <20%. Thus, the former model is much more accurate than classical models across wider volume fractions up to the disc service temperature, contributing to the design of further strengthened superalloys.