arXiv subjects

Junyuan Bai

Publications and source records attributed to Junyuan Bai.

4 recordsLinked to original sources

arXiv2025

Decoding Complex Compositions in Topologically Close-Packed Nano-plates of Magnesium Alloys: A High-Throughput Route to Stable Precipitates

Coherent topologically close-packed nanoplates in magnesium alloys can effectively improve strength and creep resistance.However, the formation mechanisms of several metastable TCP nanoplates remain unclear, and the traditional trial-and-error methods hinder the rapid discovery of novel TCP precipitate strengthened Mg alloys.By integrating the thermodynamic and kinetic conditions for TCP precipitation, we developed a two-step high-throughput screening strategy, identifying 43 previously unreported TCP nanoplates in a series of Mg alloys. These findings highlight the critical need for precise compositional characterization of nanoprecipitates and establish a theoretical framework for designing creep-resistant Mg alloys containing TCP nanoplates.

cond-mat.mtrl-sci↗

arXiv2025

First-principles Investigation of Exceptional Coarsening-resistant V-Sc(Al2Cu)4 Nanoprecipitates in Al-Cu-Mg-Ag-Sc Alloys

Aluminum-copper-magnesium-sliver (Al-Cu-Mg-Ag) alloys are extensively utilized in aerospace industries due to the formation of Omega nano-plates.However, the rapid coarsening of these nano-plates above 475 K restricts their application at elevated temperatures.When introducing scandium (Sc) to these alloys, the service temperature of the resultant alloys can reach an unprecedented 675 K, attributed to the in situ formation of a coarsening-resistant V-Sc(Al2Cu)4 phase within the Omega nano-plates. However, the fundamental thermodynamic properties and mechanisms behind the remarkable coarsening resistance of V nano-plates remain unexplored.Here, we employ first-principles calculations to investigate the phase stability of V-Sc(Al2Cu)4 phase, the basic kinetic features of V phase formation within Omega nano-plates, and the origins of the extremely high thermal stability of V nano-plates. Our results indicate that V-Sc(Al2Cu)4 is meta-stable and thermodynamically tends to evolve into a stable ScAl7Cu5 phase. We also demonstrate that kinetic factors are mainly responsible for the temperature dependence of V phase formation. Notably, the formation of V-Sc(Al2Cu)4 within Omega nano-plates modifies the Kagome lattice in the shell layer of the Omega nano-plates, inhibiting further thickening of V nano-plates through the thickening pathway of Omega nano-plates. This interface transition leads to the exceptional coarsening resistance of the V nano-plates. Moreover, we also screened 14 promising element substitutions for Sc. These findings are anticipated to accelerate the development of high-performance Al alloys with superior heat resistance.

cond-mat.mtrl-sci↗

arXiv2024

Atomic-scale Nucleation and Growth Pathway of Complex Plate-like Precipitates in Aluminum Alloys

Aluminum alloys, the most widely utilized lightweight structural materials, predominantly depend on coherent complex-structured nano-plates to enhance their mechanical properties. Despite several decades of research, the atomic-scale nucleation and growth pathways for these complex-structured nano-plates remain elusive, as probing and simulating atomic events like solid nucleation is prohibitively challenging. Here, using theoretical calculations and focus on three representative complex-structured nano-plates in commercial Al alloys, we explicitly demonstrate their associated structural transitions follow an inter-layer-sliding+shuffling mode. Specifically, partial dislocations complete the inter-layer-sliding stage, while atomic shuffling occurs upon forming the unstable basic structural transformation unit of the nano-plates. By identifying these basic structural transformation units, we propose structural evolution pathways for these nano-plates within the Al matrix, which align well with experimental observations and enable the evaluation of critical nuclei. These findings provide long-sought mechanistic details into how coherent nano-plates nucleate and grow, facilitating the rational design of higher-performance Al alloys and other structural materials.

cond-mat.mtrl-sci↗

arXiv2023

Structural pathway for nucleation and growth of topologically close-packed phase from parent hexagonal crystal

The solid diffusive phase transformation involving the nucleation and growth of one nucleus is universal and frequently employed but has not yet been fully understood at the atomic level. Here, our first-principles calculations reveal a structural formation pathway of a series of topologically close-packed (TCP) phases within the hexagonally close-packed (hcp) matrix. The results show that the nucleation follows a nonclassical nucleation process, and the whole structural transformation is completely accomplished by the shuffle-based displacements, with a specific 3-layer hcp-ordering as the basic structural transformation unit. The thickening of plate-like TCP phases relies on forming these hcp-orderings at their coherent TCP/matrix interface to nucleate ledge, but the ledge lacks the dislocation characteristics considered in the conventional view. Furthermore, the atomic structure of the critical nucleus for the Mg2Ca and MgZn2 Laves phases was predicted in terms of Classical Nucleation Theory (CNT), and the formation of polytypes and off-stoichiometry in TCP precipitates is found to be related to the nonclassical nucleation behavior. Based on the insights gained, we also employed high-throughput screening to explore several common hcp-metallic (including hcp-Mg, Ti, Zr, and Zn) systems that may undergo hcp-to-TCP phase transformations. These insights can deepen our understanding of solid diffusive transformations at the atomic level, and constitute a foundation for exploring other technologically important solid diffusive transformations.

cond-mat.mtrl-sci↗