S doped Ni, revealed different characteristic interfacial structures that underpin the embrittlement of general GBs. Recent studies of two classical GBE systems, Bi vs. However, the asymmetric and general GBs are ubiquitous and can often be the weaker link mechanically and chemically in polycrystalline materials that limit the performance. asymmetric GBs that are often of mixed tilt and twist characters) are poorly understood. The atomic-level embrittlement mechanisms of general GBs (a.k.a. Moreover, the majority of prior atomistic studies focused on symmetric tilt or twist GBs that are relatively easy to image and model. This study aims at using a classical GBE and LME system, Al–Ga (Ga-doped Al), as a model system to establish an exemplar to investigate GB composition–structure–property relationships via computing GB diagrams of thermodynamic, structural, and mechanical properties. Here, Ni–Bi 28 and Al–Ga 32, 33, 34, 38, 39, 40, 41, 42, 43 represent two classical systems that exhibit both severe GBE and LME. While there are other contributing factors, LME often occurs along with severe GBE. Liquid metal embrittlement (LME), where normally ductile metals can fail catastrophically in contact with certain liquid metals, represents a particular mystery in materials science 35, 36, 37. While the Rice–Wang model offers a general thermodynamic framework 31, the atomistic mechanisms underpinning GBE are not fully understood, defying scrutiny over a century. Specifically, GB embrittlement (GBE) induced by segregation is one of the most classical phenomena in physical metallurgy 4, 26, 28, 29, 30, 31, 32, 33, 34. adsorption in interfacial thermodynamics) at GBs can substantially alter their structural characters to influence various mechanical and other functional properties 1, 3, 4, 5, 25, 26, 27, 28, 29, 30, 31. This work strives for further constructing GB diagrams to represent not only other useful equilibrium structural characters (e.g., GB structural and chemical widths) but also computed mechanical properties. To date, GB diagrams have only been developed to represent a limited number of thermodynamic and structural properties, mostly notably adsorption (i.e., the GB excess of solutes) 18, 21, 22, 23, 24 and interfacial structural disorder 11, 14, 15, 16, 17, 21, 22, 23, 24.
Several types of GB diagrams have been computed via thermodynamic models 11, 12, 13, 14, 15, 16, 17, 18, 19, density functional theory calculations 20, atomistic simulations 21, 22, 23, and machine learning 21. Recently, it was proposed to develop the GB counterparts to bulk phase diagrams as a generally useful materials science tool 11. It has been long recognized that GBs can be treated as two-dimensional (2D) interfacial phases 7, which is more recently termed as “complexions” to differentiate them from thin GB precipitation layers of bulk (3D) phases 1, 2, 8, 9, 10. In polycrystalline materials, grain boundaries (GBs) are the ubiquitous crystal imperfection that can often control materials fabrication processing and performance 1, 2, 3, 4, 5, 6. This study suggests a research direction to investigate GB composition–structure–property relationships via computing GB diagrams of thermodynamic, structural, and mechanical (or potentially other) properties. GB diagrams are computed for not only GB adsorption and structural disorder, but also interfacial structural and chemical widths, MD ultimate tensile strength, and MD tensile toughness. Subsequently, MD tensile tests are performed on the simulated equilibrium GB structures. Simulated GB structures are validated by aberration-corrected scanning transmission electron microscopy. Specifically, hybrid Monte Carlo and molecular dynamics (MC/MD) simulations are used to obtain the equilibrium GB structure as a function of temperature and composition. Using a classical embrittlement model system Ga-doped Al alloy, this study demonstrates the feasibility of computing temperature- and composition-dependent GB diagrams to represent not only equilibrium thermodynamic and structural characters, but also mechanical properties. Computing the grain boundary (GB) counterparts to bulk phase diagrams represents an emerging research direction.