Atomic-scale analysis of liquid-gallium embrittlement of aluminum grain boundaries

Abstract

Material strengthening and embrittlement are controlled by intrinsic interactions between defects, such as grain boundaries (GB), and impurity atoms that alter the observed deformation and failure mechanisms in metals. In this work, we explore the role of atomistic-scale energetics on liquid-metal embrittlement of aluminum (Al) due to gallium (Ga). Ab initio and molecular mechanics were employed to probe the formation/binding energies of vacancies and segregation energies of Ga for <100>, <110> and <111> symmetric tilt grain boundaries (STGBs) in Al. We found that the GB local arrangements and resulting structural units have a significant influence on the magnitude of vacancy binding energies. For example, the mean vacancy binding energy for <100>, <110>, and <111> STGBs at 1 st layer was found to be -0.63 eV, -0.26 eV, and -0.60 eV. However, some GBs exhibited vacancy binding energies closer to bulk values, indicating interfaces with zero sink strength, i.e., these GBs may not provide effective pathways for vacancy diffusion. The results from the present work showed that the GB structure and the associated free volume also play significant roles in Ga segregation and the subsequent embrittlement of Al. The Ga mean segregation energy for <100>, <110> and <111> STGBs at 1 st layer was found to be -0.23 eV, -0.12 eV and -0.24 eV, respectively, suggesting a stronger correlation between the GB structural unit, its free volume, and segregation behavior. Furthermore, as the GB free volume increased, the difference in segregation energies between the 1 st layer and the 0 th layer increased. Thus, the GB character and free volume provide an important key to understanding the degree of anisotropy in various systems. The overall characteristic Ga absorption length scale was found to be about ~10, 8, and 12 layers for <100>, <110>, and <111> STGBs, respectively. Also, a few GBs of different tilt axes with relatively high segregation energies (between 0 and -0.1 eV) at the boundary were also found. This finding provides a new atomistic perspective to the GB engineering of materials with smart GB networks to mitigate or control LME and more general embrittlement phenomena in alloys.

Orientation dependences of the Fe-Li solid-liquid interface properties: Atomistic simulations

“…Yang et al [10] and Palafox-Hernandez et al [11] detailedly characterized the Al-Pb and Cu-Pb solid-liquid interface, respectively, by the density, potential energy, stress and diffusion constant profiles, as well as the two-dimensional Fourier analysis of the interfacial layers. Nam et al [4] and Rajagopalan et al [5] examined the liquid metal embrittlement of the Al-Ga system, and Nam's results agree well with both the dislocation-climb model and general trends gleaned from the experimental studies. Hashibon et al [12] created interatomic potentials for Ta-Cu system and the dewetting phenomenon of liquid Cu on Ta substrate was observed in their simulation.…”

“…According to the constituent materials we can divide them into two classes: homogeneous solid-liquid interfaces and heterogeneous solid-liquid interfaces, and the latter exist more widely. Solid-liquid interfaces play important roles in engineering ranging from solidification, melting, corrosion, to liquid metal embrittlement and so on [1][2][3][4][5][6]. Therefore they have attracted a longstanding interest from scientists and technologists, however we still know little about them for their intrinsic complexity and the limitation of M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT experimental condition.…”

The role of grain boundary structure and crystal orientation on crack growth asymmetry in aluminum

“…The periodic boundaries were maintained with a separation distance of 25 nm between the boundaries. Several 0 K minimum energy GB structures were obtained through successive rigid body translations followed by an atom deletion technique and energy minimization using a nonlinear conjugate method [24,[28][29][30][37][38][39]. In particular, grain boundary structures generated using this technique have been compared with experimental high-resolution transmission electron microscopy images [65][66][67].…”

“…Furthermore, onset of plastic deformation is complicated due to the dissociated and faceted structure present in GB interfaces [23,24]. Hence, the local structure and character of the Research has shown that GB properties are affected by both the macroscopic degrees of freedom and the microscopic local structure [25][26][27][28][29][30]. The term GB character is often used to refer to the macroscopic GB degrees of freedom.…”

Atomic-scale investigation of creep behavior in nanocrystalline Mg and Mg–Y alloys

“…As with past work [59][60][61][62][63][64][65][66][67] and others [68][69][70], an atom deletion criterion, multiple initial configurations, and various in-plane rigid body translations were utilized to accurately obtain an optimal minimum energy GB structure via the nonlinear conjugate gradient energy minimization process. Further details on the GB generation technique and GB structures of HCP materials are given in Bhatia and Solanki [59], and Wang and Beyerlein [71].…”