Precipitate phase selection and grain boundary morphology in Cu-Ni-Si-Mn alloys: A machine-learning interatomic potential study

Aadil Fayaz Wani; Il-Seok Jeong; Haekwan Jeon; Jaesun Kim; SuDong Park; Eun-Ae Choi; Seung Zeon Han; Seungwu Han; Byungki Ryu

paper

Precipitate phase selection and grain boundary morphology in Cu-Ni-Si-Mn alloys: A machine-learning interatomic potential study

arXiv:2606.09023

Abstract

Alloys inevitably contain interphase boundaries, whose energetics govern nucleation processes and precipitate morphology. In Cu-Ni-Si alloys, Mn addition markedly changes grain boundary (GB) precipitation behavior. While GB precipitation of stable Ni $_{2}$ Si in Mn-free alloys is associated with degraded mechanical properties, Mn addition instead promotes film-shaped Mn $_{6}$ Ni $_{16}$ Si $_{7}$ (G-phase) precipitation, which is correlated improved mechanical properties. However, the atomic origin of the contrasting GB phase selection and morphology remains unclear. Here we perform machine-learning interatomic potential (MLIP) calculations to investigate the effect of interphase-boundary atomic structure on GB precipitates in Cu-Ni-Si alloys with and without Mn. The MLIP calculations reliably reproduce DFT-level energetics for interfacial bonding and microstructural configurations, and further predict that Mn addition favors GB precipitation of Mn $_{6}$ Ni $_{16}$ Si $_{7}$ rather than Ni $_{2}$ Si. Experimentally, Mn-free alloys are observed to exhibit irregularly-shaped Ni $_{2}$ Si precipitates with open-boundary-like Cu/Ni $_{2}$ Si interfaces, whereas Mn-added alloys exhibit film-like G-phase at GBs. Large-scale atomistic interface calculations reveal that the coherent interface structure between Cu and Ni $_{2}$ Si favors the formation of plate-like strained Ni $_{2}$ Si precipitates in the matrix. Upon coarsening and stress release, an out-of-phase coherent-like interface can form at GBs, generating a local repulsive region that gives rise to surface-like open-boundary structures and explains the irregular morphology of GB stable Ni $_{2}$ Si precipitates. In contrast, Cu/Mn $_{6}$ Ni $_{16}$ Si $_{7}$ interfaces remain predominantly incoherent with moderate boundary energies and no pronounced repulsive regime, thereby stabilizing continuous interfacial contact and explaining film-shaped GB precipitation.

45 pages, 3 tables, 9 figures, 61 references, 3 SM tables, 2 SM figures