Papers by Author: C. Schäfer

Abstract: In this study we aim at combining the results from transmission electron microscopy (TEM) and atom probe tomography (APT) to study the early stages of phase decomposition in the age hardening alloy AA 6016. Samples are subjected to different periods of natural ageing or artificial pre-ageing at elevated temperature in order to produce different types of clusters and early stages of precipitation before age hardening commences. APT is utilized to detect clusters and identify their compositions, whereas TEM is applied to analyse and quantify number density and sizes of the particles during artificial ageing at 185°C. It is shown that the two techniques, TEM and APT, are complementary and a combined approach yields more detailed insight into the early stages of phase decomposition in age hardening 6xxx series alloys than possible by the sole use of either technique individually.

Abstract: In the present study, nucleation at Cube bands during annealing of a cold rolled commercial aluminium alloy AA8079 was investigated. The main goal of this work was to provide experimental data for subsequent modelling. By studying the deformed material the geometrical parameters of Cube bands were determined. The Cube band spacing in the deformed state was measured experimentally and accordingly calculated with a simple geometric model, taking the initial Cube fraction in the pre-deformed state and the deformation degree into account. The nucleation frequency during subsequent annealing of the cold deformed material was estimated from the geometry and size of deformed Cube bands prior to deformation. From investigations of the orientation relationship between the Cube oriented nuclei and the adjacent deformed matrix with S orientation, the fraction of 40°<111> grain boundaries having optimum growth conditions, was established.

Abstract: A refined view of particle stimulated nucleation of recrystallization is presented, which utilizes a combination of advanced modeling tools. FEM simulations were carried out in order to model the evolution of the deformation zone around particles for various particle sizes and shapes. The results of these simulations were complemented by EBSD measurements to determine the number and orientation of nuclei. Finally, this information on particle stimulated nucleation was incorporated into a 3D cellular automaton recrystallization model CORe to model microstructure evolution. From these simulations the dependence of grain size and texture on particles size and shape was derived.

Abstract: The predictions from a grain cluster deformation texture model, GIA, are utilized to study the nucleation texture of recrystallisation of aluminium alloys. In combination with a dislocation based work hardening model, the propensity of specific grains in their granular environment for select nucleation mechanisms is investigated. Quantitative criteria for the nucleation events can be formulated. The results can be fed into a growth model of recrystallisation to predict recrystallisation textures and lend themselves to through-process modelling.