Energetics of vacancy segregation to symmetric tilt grain boundaries in hexagonal closed pack materials

Bhatia, M. A.; Solanki, Kiran

doi:10.1063/1.4858401

Cited by 42 publications

(33 citation statements)

References 42 publications

(45 reference statements)

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“…Altogether, this entailed ~150,000 MS calculations to quantify the vacancy formation/binding energy statistics. The vacancy formation energy at a site  is , where is the cohesive energy/atom in a perfect fcc lattice, and and are the total energies of the GB simulation cell with and without the vacancy, respectively [72,73]. It is useful to reference the vacancy formation energy at the grain boundary to that in the bulk (1) in order to assess the energy required to move the vacancy from the boundary into the bulk or vice versa.…”

Section: Methodsmentioning

confidence: 99%

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

et al. 2014

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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.

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Section: Methodsmentioning

confidence: 99%

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

et al. 2014

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“…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].…”

Section: Equilibrium Grain Boundary Structuresmentioning

confidence: 99%

“…Historically, many efforts have focused on developing a method to characterize GBs [31][32][33][34][35][36] and their influence on the physical properties of polycrystalline material (e.g. [37][38][39]). These models utilized dislocation arrays, disclinations, and coincident site lattice (CSL) to describe microscopic and macroscopic degrees of freedom of GBs.…”

Section: Introductionmentioning

confidence: 99%

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

Adlakha

Tschopp

Solanki

2014

Materials Science and Engineering: A

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Atomistic simulations have shown that the grain boundary (GB) structure affects a number of physical, mechanical, thermal, and chemical properties, which can have a profound effect on macroscopic properties of polycrystalline materials. The research objective herein is to use atomistic simulations to explore the role that GB structure and the adjacent crystallographic orientations have on the directional asymmetry of an intergranular crack (i.e. cleavage behavior is favored along one direction, while ductile behavior along the other direction of the interface) for aluminum grain boundaries. Simulation results from seven <110> symmetric tilt grain boundaries (STGBs) show that the GB structure and the associated free volume directly influence the stress-strain response, crack growth rate, and crack tip plasticity mechanisms for middle-tension (M(T)) crack propagation specimens. In particular, the structural units present within the GB promote whether a dislocation or twinning-based mechanism operates at the crack tip during intergranular fracture along certain GBs (e.g., the 'E' structural unit promotes twinning at the crack tip in Al). Furthermore, the crystallography of the adjacent grains, and therefore the available slip planes, can significantly affect the crack growth rates in both directions of the crack -this creates a strong directional asymmetry in the crack growth rate in the Σ11 (113) and the Σ27 (552) STGBs. Upon comparing these results with the theoretical Rice criterion, it was found that certain GBs in this study (Σ9 (221), Σ11 (332) and Σ33 (441)) show an absence of directional asymmetry in the observed crack growth behavior, in conflict with the Rice criterion. The significance of the present research is that it provides a physical basis for the role of GB character and crystallographic orientation on intergranular crack tip deformation behavior.

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“…Because the mechanical behavior and fracture of polycrystalline materials is often driven by grain boundaries and their underlying structure [2][3][4], a fundamental understanding of the relationship between the grain boundary structure and associated properties is important to develop interface-dominant materials. Research has shown that both the macroscopic degrees of freedom and microscopic local structure affect the physical properties of grain boundaries [5][6][7][8][9][10][11][12]. The term grain boundary character is often used to describe the five degrees of freedom necessary to define a grain boundary.…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Segregation of Interstitial and Substitutional Impurity Atoms in Alpha-Iron

Rajagopalan

Tschopp

Solanki

2013

JOM

Self Cite

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The macroscopic behavior of polycrystalline materials is influenced by the local variation of properties caused by the presence of impurities and defects. The effect of these impurities at the atomic scale can either embrittle or strengthen grain boundaries within. Thus, it is imperative to understand the energetics associated with segregation to design materials with desirable properties. Here, molecular statics simulations were employed to analyze the energetics associated with the segregation of various elements (helium, hydrogen, carbon, phosphorous, and vanadium) to four <100> (5 and 13 GBs) and six <110> (3,9,and11 GBs) symmetric tilt grain boundaries in alpha-Fe. This knowledge is important for designing stable interfaces in harsh environments. Simulation results show that the local atomic arrangements within the GB region and the resulting structural units have a significant influence on the magnitude of binding energies of the impurity (interstitial and substitutional) atoms. This data also suggests that the site-to-site variation of energies within a boundary is substantial. Comparing the binding energies of all ten boundaries shows that the 3(112) boundary possesses a much smaller binding energy for all interstitial and substitutional impurity atoms among the boundaries examined here. Additionally, based on the Rice-Wang model, our total energy calculations show that V has a significant beneficial effect on the Fe grain boundary cohesion, while P has a detrimental effect on grain boundary cohesion, much weaker than H and He. This is significant for applications where extreme environmental damage generates lattice defects and grain boundaries act as sinks for both interstitial and substitutional impurity atoms. This methodology provides us with a tool to effectively identify the local as well as the global segregation behavior which can influence the GB cohesion.

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Energetics of vacancy segregation to symmetric tilt grain boundaries in hexagonal closed pack materials

Cited by 42 publications

References 42 publications

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

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

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

Grain Boundary Segregation of Interstitial and Substitutional Impurity Atoms in Alpha-Iron

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