M2 Al-based alloys
| Dr. Sergiy Divinsky | Dr. Tilmann Hickel |
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| divin@uni-muenster.de | hickel@mpie.de |
Al-based alloys are important industrial materials in view of a continuously rising demand for high strength and light-weight alloys for structural applications. A combination of ultra-fine grained (UFG) microstructure formation, grain size strengthening and precipitation hardening offers an attractive route to produce semi-finished products with high strength and endurance limit, good ductility and sufficient fracture toughness. In the case of Al-Mg-Sc alloys it has been recently discovered that the formation of an UFG microstructure can significantly affect the size and morphology of second-phase precipitates, as well as their chemistry and distribution within the Al matrix. It is therefore the aim of the present project to understand and resolve the coupling between thermo-chemistry and thermo-mechanics underlying these processes. To achieve this goal, ab initio based atomistic simulations, accompanied by dedicated and carefully selected experiments will be performed. The effect of the stress field caused by the microstructure and external loads on the local chemistry will on the one hand be accurately determined by performing fully temperature-dependent calculations within density functional theory, which also take anharmonic entropy contributions into account. On the other hand, to simulate precipitate formation under strongly strained conditions a kinetic Monte-Carlo scheme that allows to include medium and long range elastic interactions will be developed. The coupled thermodynamic-kinetic approach will not only allow a detailed analysis of how large local strain fields affect the formation and chemistry of precipitates, but also the opposite route, i.e. how the formation of a new chemical phase (precipitates) affects the mechanical strain fields. The development of a reliable method and understanding is not possible without careful comparisons and benchmarks against well-selected and project specific measurements. In-depth analyses of the microstructure in the UFG alloys is obtained by transmission electron microscopy (TEM) and related methods. Here, in particular the geometrical phase analysis (GPA) will provide quantitative data of the strain field and precipitate distribution in the vicinity of grain boundaries. In parallel, radio-tracer diffusion experiments will provide data on how mechanical deformations change the chemical composition and structure of the grain boundary and affect diffusion mobilities. The synergy effects of this joined experimental and theoretical approach will allow to systematically explore the mechano-chemical coupling in a technologically relevant materials system and to improve our fundamental understanding of the complex interplay between strain, chemistry.