Application of the HAI-model to the creep behaviour of particle hardened nickel-base superalloys

Abstract The Haasen-Alexander-Ilschner (HAI-) theory of internal and effective stress is combined with the modified threshold stress (σ p ) concept in order to describe steady-state as well as transient creep deformation of oxide dispersion strengthened (ODS) nickel-base superalloys under constant strain rate (ġ3) conditions. The microstructurally based model correctly reflects the steady-state relationship of ġ3 and σ at large plastic strains. For any given constant ġ3-value the fine dispersed incoherent Y 2 O 3 particles in MA 754 rise the stress level considerably compared to the single-phase solid solution, Nimonic 75, of similar chemical composition. The higher contents of Al and Ti in MA 6000 lead to additional precipitation hardening of coherent γ′-particles and a further increase in stress. However, transient creep can only be modelled by splitting σ p into two additive terms: firstly a constant σ p * value representing the contribution for the mere particle overcoming process and secondly an increasing σ ϱ,p term reflecting the building up of geometrically necessary dislocations during plastic deformation.