Strength of γ′ hardened nickel-base alloy

Abstract

Results from isothermal ageing of a commercial nickel-base alloy are presented. Particle sizes are determined by electron microscopy. The particle coarsening is found to obey the Lifschitz-Wagner theory. The volume fraction of γ′ particles is 0.15. The proof stress is determined for a series of ageing times. The Taylor factor is calculated taking the texture of the material into account.

A theory is presented for the critical resolved shear stress due to γ′ particles. The motion of a pair of dislocations is considered. The dislocations interact with the particles through the generation of antiphase boundary and through the misfit strain field. The dissociation of the dislocations into partials is taken nto account. A line tension model is used which depends on the dislocation configuration. A statistical theory is used to calculate the critical resolved shear stress from a three-dimensional distribution of particles. A good agreement between theory and experiment is obtained by using an antiphase boundary energy of 0.19 J m⁻² and a constrained misfit ratio of 0.35% for the particles. Antiphase boundary hardening accounts for approximately half of the particle-induced strength of the alloy.