SPP 1713 Subproject: Mechano-chemical coupling during precipitate formation in Al-based alloys
Basic data for this project
Type of project: Subproject in DFG-joint project hosted outside University of Münster
Duration: 01/07/2017 - 30/06/2020 | 2nd Funding period
Description
Al-based alloys are important industrial materials in view of a continuously rising demand for high strength andlight-weight alloys for structural applications. A combination of ultra-fine grained (UFG) microstructureformation, grain size strengthening and precipitation hardening offers an attractive route to producesemi-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 cansignificantly affect the size and morphology of second-phase precipitates, as well as their chemistry anddistribution within the Al matrix. It is therefore the aim of the present project to understand and resolve thecoupling between thermo-chemistry and thermo-mechanics underlying these processes.To achieve this goal, ab initio based atomistic simulations, accompanied by dedicated and carefully selectedexperiments will be performed. The effect of the stress field caused by the microstructure and external loadson the local chemistry will on the one hand be accurately determined by performing fullytemperature-dependent calculations within density functional theory, which also take anharmonic entropycontributions into account. On the other hand, to simulate precipitate formation under strongly strainedconditions a kinetic Monte-Carlo scheme that allows to include medium and long range elastic interactions willbe developed. The coupled thermodynamic-kinetic approach will not only allow a detailed analysis of how largelocal strain fields affect the formation and chemistry of precipitates, but also the opposite route, i.e. how theformation 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 andbenchmarks against well-selected and project specific measurements. In-depth analyses of the microstructurein the UFG alloys is obtained by transmission electron microscopy (TEM) and related methods. Here, inparticular the geometrical phase analysis (GPA) will provide quantitative data of the strain field and precipitatedistribution in the vicinity of grain boundaries. In parallel, radio-tracer diffusion experiments will provide data onhow mechanical deformations change the chemical composition and structure of the grain boundary and affectdiffusion mobilities.The synergy effects of this joined experimental and theoretical approach will allow to systematically explore themechano-chemical coupling in a technologically relevant materials system and to improve our fundamentalunderstanding of the complex interplay between strain, chemistry, structure, kinetics of interfaces, precipitateformation and their reverse effect on the mechanical response.
Keywords: aluminium alloy; precipitation hardening; grain boundary; ab initio; tracer diffusion; high-resolution TEM