Mechano-chemical coupling during precipitate formation in Al-based alloys

• Applicants: Professor Dr. Sergiy Divinski; Dr. Tilmann Hickel
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257547071

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 attractive routes 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 the formation of an UFG microstructure can significantly affect the structure, chemistry and distribution of second-phase precipitates within the Al matrix. Technical alloys with the additional solutes Zr, Ti, Mg and Mn give rise to additional phenomena like the formation of core-shell nanoparticles. 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 also be performed in the second period of the project. The investigation of the effect of the stress field caused by the microstructure and external loads on the local chemistry and thermodynamics will be extended to multicomponent systems. Moreover, to simulate precipitate formation under strongly strained conditions a new kinetic Monte-Carlo scheme that allows to include medium and long range elastic interactions will be applied. 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. Highlights of the second phase are the formation of core-shell-nanoparticles and the influence of grain boundaries. The development of a reliable method and understanding is not possible without careful comparisons and benchmarks against well-selected and project specific measurements. Compression-shear deformation experiments will provide new insights into the distribution of precipitates. An in-depth analyses of the microstructure and local chemistry in the UFG alloys is obtained by transmission electron microscopy and related methods. In parallel, radio-tracer diffusion experiments under load will provide data on how mechanical deformations affect the chemical composition and 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, structure, kinetics of interfaces, precipitate formation and their reverse effect on the mechanical response.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1713: Strong Coupling of Thermo-Chemical and Thermo-Mechanical States in Applied Materials
• Co-Investigators: Professor Dr. Jörg Neugebauer; Professor Dr.-Ing. Gerhard Wilde