Micromechanical modelling of fundamental creep mechanisms in superalloy single crystals.
The typical microstructure of single crystalline superalloys contains relatively soft narrow γ-matrix channels and hard cubic γ′-precipitates. This microstructure confines and controls dislocation motion by slip and climb, and decisively influences dislocation evolution mechanisms including multiplication and annihilation.
Experimental and modelling results show that in the primary creep stage dislocation loops expand inside the matrix channels and leave screw or mixed dislocation lines in different γ/γ′-phase boundaries. Although it is often assumed that dislocations move along the interfaces by a combination of slip and climb steps and that this motion leads to a recombination and annihilation of dislocation in the channel vertices, it is not clear how this diffusion-assisted mechanism operates on length scales of several micrometres. Hence, it is also not understood to which extend this dynamic recovery process affects the creep rates for given microstructures and thermo-mechanical loads. To understand and formulate the elementary dislocation mechanisms of migration along interfaces and also precipitate cutting is consequently a critical step to model creep deformation in a realistically wide temperature and stress range where the effectiveness of the γ/γ′-strengthening mechanism undergoes severe changes. This proposal aims at studying the elementary creep mechanisms on the length scale of dislocation networks and to extend these micromechanical models to the macroscale with the help of microstructurally informed crystal plasticity formulations. These latter plasticity models allow for a prediction of macroscopic properties, like the minimum creep rate, that can be directly compared to results of mechanical testing.
The project is carried out and funded in the framework of the SFB/TR103 "Superalloy Single Crystals".