Author(s)

A. Staroselsky & B. Cassenti

Abstract

The micromechanics of the high temperature creep and damage accumulation in single crystal nickel base superalloys is important for the design of turbine blades and vanes in advanced commercial and military gas turbines. We have developed a robust predictive tool to relate single crystal macroscopic behaviour and fracture initiation to micromechanical events. A crystallographic-based model for non-isothermal high temperature cyclic deformation has been fully coupled with the damage kinetics. The model significantly improves the quality of material deformation predictions on cyclic and thermal-cyclic loading. Keywords: super-alloys, single crystal, constitutive modeling, dislocation kinetics. 1 Introduction Historically, secondary creep effects with associated modelling techniques (Larson-Miller, etc.) were used in engineering calculations. However, during the thermal-mechanical loading of high temperature single crystal turbine parts, all three creep stages: primary, secondary and tertiary, manifest themselves and none of them can be neglected. A creep law is especially important in the case of non-homogeneous thermal loading which results in intensive stress redistribution and relaxation. Several damage mechanisms, namely multiplication of mobile dislocations, void and micro-crack growth and the scale effects caused by dislocation extrusions/intrusions and necking, have been considered. Our damage model bridges the gap between dislocation dynamics and continuum mechanics scales. Damage accumulation causes tertiary creep and shear localization around local concentrators, which is essential for airfoil life prediction.

Keywords

super-alloys, single crystal, constitutive modeling, dislocation kinetics.