Abstract
The effects of anisotropic interfacial properties and heterogeneous elasticity on the growth and ripening of plate-like θ′-phase (Al2Cu) in Al-1.69 at.% Cu alloy are studied. Multi-phase-field simulations are conducted and discussed in comparison with aging experiments. The precipitate/matrix interface is considered to be anisotropic in terms of its energy and mobility. We find that the additional incorporation of an anisotropic interfacial mobility in conjunction with the elastic anisotropy result in substantially larger aspect ratios of the precipitates closer to the experimental observations. The anisotropy of the interfacial energy shows comparably small effect on the precipitate’s aspect ratio but changes the interface’s shape at the rim. The effect of the chemo-mechanical coupling, i.e., the composition dependence of the elastic constants, is studied as well. We show that the inverse ripening phenomenon, recently evidenced for δ’ precipitates in Al-Li alloys (Park et al. Sci. Rep. 2019, 9, 3981), does not establish for the θ′ precipitates. This is because of the anisotropic stress fields built around the θ′ precipitates, stemming from the precipitate’s shape and the interaction among different variants of the θ′ precipitate, that disturb the chemo-mechanical effects. These results show that the chemo-mechanical effects on the precipitation ripening strongly depend on the degree of sphericity and elastic isotropy of the precipitate and matrix phases.
Highlights
Understanding the precipitation process is of paramount importance for developing Al alloys
A key complicating factor is the mutual interplay between these phenomena, i.e., the chemo-mechanical coupling between diffusing solutes and the stress fields around a precipitate, amplified by the small size of the precipitates
We further study precipitation ripening in the presence of chemo-mechanical coupling, i.e., the composition dependence of the elastic constants in the matrix [1,9,10]
Summary
Understanding the precipitation process is of paramount importance for developing Al alloys. Analytical [22,23,24] and experimental [25,26,27,28] investigations showed that the physical mechanism for plate thickening of the θ0 phase is the motion of ledges across the broad face that need to nucleate in the first place, while along the θ0 rim atoms attach to the already existing ledges This motivates that the interface mobility can be rather anisotropic. The experimental determination of this parameter is described by Heugue for the θ0 -Al2 Cu and θ-Al2 Cu precipitates in a binary Al-3.5 wt.% Cu alloy [30] These suggest that the influence of the interface mobility on the precipitate shape might need a more detailed investigation. The effects of stress fields on the precipitate ripening with and without the chemo-mechanical coupling effects are compared
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