M1 Precipitation and creep in Al alloys
| Prof. Dr.-Ing. Birgit Skrotzki | Dr.-Ing. Reza Darvishi Kamachali |
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| birgit.skrotzki@bam.de | kamachali@mpie.de |
Coherent/semi-coherent precipitates obtained per aging are important strengthener of light and tough materials such as Al-alloys, involving phase transformation and change of internal stress and local composition states. While the response of these materials to the external load at service temperatures crucially depends on the fraction, composition and local distribution of the precipitates, in return, the external/internal stresses strongly influence stability, arrangement and growth of the strengthening phases.
In this project we address formation, growth and ripening of the strengthening precipitates and micro-voids during standard aging, aging under load and continued loading (creep) with a specific consideration on the mutual cooperation between external load and internal self-stress to the local chemical composition and vacancy concentration. To express this coupling, a thermodynamically consistent phase-field model will be constructed and will be combined with experimental validations. Al – 4%Cu – 1%Li – 0.25%Mn alloy (wt. %) is chosen as an applied model-alloy with two important classes of precipitates to mimic real multi-component Al-alloys. One important aspect to be addressed is the dynamics of non-equilibrium vacancies on the kinetics of precipitation and stress-driven void formation as it happens under creep conditions. The model development and simulation results will be validated by high-temperature creep experiments and subsequent microstructural characterizations involving SEM, HRTEM, and GPA.
Precipitation under chemo-mechanical coupling: example of Ni4Ti3 in shape memory alloys.
Coupling mechanical effects to the interface: vacancy (as strain sources) hinder growth on the nanoscale.
Creep test machines (BAM).
Aging under load: left) Normal aging versus right) ageing under load in Al alloys.