Stress-field Driven Solute Segregation and Heterogeneous Nucleation in Alcu Alloys: A Phase-Field Study of Multiscale Defect Engineering

The mechanistic role of defect stress fields in modulating solute segregation and heterogeneous nucleation in AlCu alloys remains unclear. Here, we develop a multiphase-field model that couples the Cu concentration field, θ' precipitates, and elastic stress fields to investigate the effects of dislocation lines, low-angle grain boundaries, and coarse θ phases, supplemented by dislocation loop cases to demonstrate the design potential. The simulations quantitatively reproduce the orientation-dependent nucleation and growth of θ' variants, which are validated by STEM observations. A universal cascade mechanism is established: defect stress fields drive directional Cu segregation into enriched zones, which serve as the compositional precursors governing nucleation sites, variant orientation, and growth kinetics. Quantitative analysis further reveals that the spatial distribution and intensity of the stress fields directly influence the degree of solute segregation, while their spatial geometric characteristics lead to significant differences in both the average diameter and volume fraction of θ' precipitates. This study demonstrates that tailoring the geometric features of stress fields offers a viable route for the deliberate design of precipitation microstructures, providing a general framework extendable to other precipitation-hardened alloy systems.