Creep lifetime prediction of oxide-dispersion-strengthened nickel-base superalloys: A micromechanically based approach

Abstract

The high-temperature creep behavior of the oxide-dispersion-strengthened (ODS) nickel-base superalloys MA 754 and MA 6000 has been investigated at temperatures up to 1273 K and lifetimes of approximately 4000 hours using monotonic creep tests at constant true stressσ, as well as true constant extension rate tests (CERTs) at$\dot \varepsilon$. The derivation of creep rupture-lifetime diagrams is usually performed with conventional engineering parametric methods, according to Sherby and Dorn or Larson and Miller. In contrast, an alternative method is presented that is based on a more microstructural approach. In order to describe creep, the effective stress model takes into account the hardening contributionσ _p caused by the presence of second-phase particles, as well as the classical Taylor back-stressσ _p caused by dislocations. The modeled strain rate-stress dependence can be transferred directly into creep-rupture stress-lifetime diagrams using a modified Monkman-Grant (MG) relationship, which adequately describes the interrelation between$\dot \varepsilon$ representing dislocation motion, and lifetimet _f representing creep failure. The comparison with measured creep-rupture data proves the validity of the proposed micromechanical concept.