Precipitates including Al
3
Li, Al
3
Zr and core–shell structured Al
3
Li (Al
3
Zr) produce significant strengthening effects in Al-Li alloys by means of anti-phase boundaries and dislocation ...looping. However, the precipitate/metal interfacial structures and precipitate formation mechanisms in Al-Li alloys remain unclear due to the lack of advanced experimental methods. In this work, atomic-scale structural models of Al
3
Li/Al, Al
3
Zr/Al, and Al
3
Li/Al
3
Zr interfaces are created, while bridge-, top-, hollow-, and center-stacking sequences are applied, respectively. Within these models, Al slabs with 5 atom layers and Al
3
Li and/or Al
3
Zr slabs with 6 atom layers are selected in which interfacial orientations of (100), (110), and (111) are considered. For the Al
3
Li/Al, Al
3
Zr/Al, and Al
3
Li/Al
3
Zr interfaces, the structural models with bridge- and hollow-stacking sequences generate the most stable energy-based interfaces. Moreover, the nucleation free energies of the core-shell structured Al
3
Zr(Al
3
Li) are larger than those of the isolated Al
3
Li+Al
3
Zr and core-shell structured Al
3
Li(Al
3
Zr), leading to the absence of the core-shell structured Al
3
Zr(Al
3
Li) in most experimental observations. Further studies of the uniaxial tensile mechanical properties of the Al
3
Li/Al, Al
3
Zr/Al, and Al
3
Li/Al
3
Zr interfaces revealed that the Al
3
Zr/Al interfaces possess larger Young’s moduli and tensile strengths than those of the Al
3
Li/Al and Al
3
Li/Al
3
Zr interfaces. In conclusion, the interfacial stability, precipitate formation and mechanical behaviors of Al
3
Li/Al
3
Zr/Al interfaces are elucidated for the development of Al-Li alloys and their composites.
•Atomic-scale simulation methodologies and structural models of nanocarbon reinforced metal matrix composites (MMCs) are summarized.•Tensile, compressive, shear and bending mechanical behaviors of ...nanocarbon reinforced MMCs via atomic-scale simulations are reviewed.•Multi-scale simulations of nanocarbon reinforced MMCs are discussed to couple atomic-scale simulations with continuum-scale finite element analysis.•Multi-scale simulation platforms containing materials database, machine learning and parallel computing are expected to uncover the structure-property relationships of advanced MMCs.
Due to their excellent mechanical properties including high modulus, high strength, large ductility and low density, nanocarbon like the graphene (Gr) and carbon nanotubes (CNTs) have become potential reinforcements in metal matrix composites (MMCs). Dislocation impediment and load transfer across nanocarbon/metal interfaces could strengthen the nanocarbon reinforced MMCs as well as micro-/nano-scale hybrid MMCs. Due to complex composite structures and interfacial microstructures, large difficulties exist in indicating the microscopic structure-property relationships by continuum mechanical simulations and experimental approaches. Considering the situations above, the atomic-scale simulations including first-principles and molecular dynamics simulation are suitable to investigate the microscopic structure-property relationships of nanocarbon reinforced MMCs, in which the physical properties, crystal orientations, interfacial structures and mechanical behaviors could be studied under a wide range of working temperatures and strain rates, etc. In recent years, the development of advanced computation techniques including material database, machine learning and parallel computing have enlarged the research works in the atomic-scale simulations of nanocarbon reinforced MMCs. Therefore, a systematical review of atomic-scale simulation and mechanical behaviors of nanocarbon reinforced MMCs is conducted in this study. Atomic-scale simulation methodologies are first introduced, while the atomic-scale structural models of nanocarbon reinforced MMCs are discussed as follows. Next, different atomic-scale mechanical deformations containing tensile, compressive, shear and bending mechanical deformations of nanocarbon reinforced MMCs are summarized. Moreover, the multi-scale simulations of nanocarbon reinforced MMCs are reviewed as well, while the perspectives of atomic-scale simulations of nanocarbon reinforced MMCs are suggested for the future research works based on advanced computation techniques.
An intrinsic feature of nearly all internal interfaces in crystalline systems (homo- and hetero-phase) is the presence of disconnections, namely topological line defects constrained to the interface ...that have both step and dislocation character. We demonstrate that elastic interactions between disconnections strongly affect the morphology and motion of interfaces, allowing for understanding and reconciling diverse key experiments. In particular, these elastic interactions strongly modify equilibrium interface morphologies compared with those solely determined by anisotropic surface energy, and affect the kinetics of migrating interfaces. They are also found to lead to a thermodynamic, first-order, finite-temperature, faceting–defaceting transition. We demonstrate these phenomena through numerical simulations based upon a general, continuum disconnection-based model for interface thermodynamics and kinetics applied to embedded particles/grains, steady-state interface migration geometries, and nominally flat interfaces.
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Disconnection flow-mediated grain rotation Qiu, Caihao; Salvalaglio, Marco; Srolovitz, David J ...
Proceedings of the National Academy of Sciences - PNAS,
01/2024, Letnik:
121, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Grain rotation is commonly observed during the evolution of microstructures in polycrystalline materials of different kinds, including metals, ceramics, and colloidal crystals. It is widely accepted ...that interface migration in these systems is mediated by the motion of line defects with step and dislocation character, i.e., disconnections. We propose a crystallography-respecting continuum model for arbitrarily curved grain boundaries or heterophase interfaces, accounting for the disconnections' role in grain rotation. Numerical simulations demonstrate that changes in grain orientations, as well as interface morphology and internal stress field, are associated with disconnection flow. Our predictions agree with molecular dynamics simulation results for pure capillarity-driven evolution of grain boundaries and are interpreted through an extended Cahn-Taylor model.
Developing metal matrix composites (MMCs) with hybrid reinforcements becomes a promising approach to balance and improve their strengths and toughness. However, due to complexity of multiphase ...interfacial micro-zones and lack of suitable research method, difficulties are still existing in revealing the structure-property relationship of hybrid MMCs. In this work, molecular dynamics simulations are conducted to study microstructural characteristics and mechanical behavior of SiC(CNT)/Al multiphase interfacial micro-zones under uniaxial tensions. Six atomic-scale structural models of SiC/Ni/CNT, SiC/Al, SiC/Ni/CNT(l)/Al, SiC/CNT(l)/Al SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al (l: long, s: short) interfacial micro-zones are created, respectively. Compared with those of SiC/Al interfacial micro-zone, improved tensile ductility and toughness are achieved in the SiC/Ni/CNT(l)/Al, SiC/CNT(l)/Al, SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones, where lots of dislocations, larger dislocation densities and continuously increasing equivalent shear strains appear. SiC/Ni/CNT(l)/Al and SiC/CNT(l)/Al interfacial micro-zones with long CNT clusters could produce large Young's modulus, while those of SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones are relatively low caused by poorly load-transferring. Tensile fracture of SiC/Al interfacial micro-zone occurs at the SiC/Al interface due to the local concentrations of both dislocations and plastic deformation, while those of SiC/Ni/CNT(l)/Al, SiC/CNT(l)/Al SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones all happen in the Al matrix close to the bottom ends of CNTs and SiC. From the analysis above, the microstructural characteristics and mechanical behavior of SiC(CNT)/Al multiphase interfacial micro-zones can be brought into light, which would be applied to design and fabricate smart multiphase MMCs.
Micro-sized silicon carbide particles (SiCp) reinforced aluminum (Al) matrix composites have been widely used in the aerospace, electronics and transportation applications. However, due to the easily ...formed stress concentration in the SiCp/Al interfacial micro-zones, the large-sized SiCp may cause serious plastic loss of SiCp/Al composites that have limited their applications. In this study, the 14.5 μm SiCp was selected to prepare the SiCp(CNT) hybrid reinforcement, and then the 15 wt. % SiCp/Al and SiCp(CNT)/Al composites were fabricated by the vacuum hot-pressing sintering, respectively. Compared to the SiCp/Al composite, the SiCp(CNT)/Al composites own the larger mechanical properties such as the Young's modulus, the yield strength and the tensile strength. Among these composites, the SiCp(0.5CNT)/Al composite presents the best matching of strength and plasticity as a result of the existence of CNTs in the SiCp/Al interfacial micro-zones. Strengthening and toughening effects of CNTs in the SiCp/Al interfacial micro-zones can contribute to: 1) increasing the punched zone size around the SiCp; 2) increasing the dislocation density in the SiCp/Al interfacial micro-zones; 3) changing the dislocation distributions in the SiCp/Al interfacial micro-zones; 4) pinning the dislocation movements by CNTs in the SiCp/Al interfacial micro-zones. From the analysis above, the strengthening and toughening mechanism of the CNTs introduced in the SiCp/Al interfacial micro-zones of SiCp(CNT)/Al composites can be revealed, which can be further developed to guide and prepare the hybrid particles reinforced metal matrix composites.
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•The strength-plasticity matching relationship of SiCp/Al composites can be improved by the presence of CNTs at the interface micro-zones.•Compared with SiCp/Al composites, the introduction of CNTs can increase the dislocation density at the interface micro-zones and pin the dislocation movement.•The existence of CNTs can change the dislocation distribution of SiCp/Al interface micro-zones.
Grain boundaries are Brownian ratchets Qiu, Caihao; Punke, Maik; Tian, Yuan ...
Science (American Association for the Advancement of Science),
08/2024, Letnik:
385, Številka:
6712
Journal Article
Recenzirano
We demonstrate that grain boundaries (GBs) behave as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under oscillatory driving forces or cyclic thermal ...annealing. We observed these phenomena for nearly all nonsymmetric GBs but not for symmetric ones. Our observations build on molecular dynamics and phase-field crystal simulations for a wide range of GB types and driving forces in both bicrystal and polycrystalline microstructures. We corroborate these simulation results through in situ experimental observations. We analyze these results with a Markov chain model and explore the implications of GB ratchet behavior for materials processing and microstructure tailoring.
Editor’s summary The grain size of a polycrystalline material is one important part of the microstructure that constrains the properties. In contrast to previous assumptions, Qiu et al . have shown through modeling that grain boundaries can move in one direction in response to a nondirectional driving force. However, not all grain boundary types do so, mostly just the ones that are geometrically nonsymmetric. This observation helps us better understand some grain-coarsening behavior and may also be another tool for engineering microstructures and improving the material properties. —Brent Grocholski
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•Atomic-scale interfacial models are built by different terminations and stacking sequences.•C-top and Si-top models provide most stable structures according to interfacial ...stability.•They possess largest tensile interfacial properties and fractures almost happen in Al matrix.•Interfaces deform along 11¯0 direction and Al atoms slip along 101¯ and 1¯01 directions.
In this work, the interfacial stability, mechanical behavior and failure mechanism of β-SiC(1 1 1)/Al(1 1 1) interfaces are systematically investigated by the first-principles simulations based on density functional theory. By stacking the Al(1 1 1) slab with five atom-layers on the β-SiC(1 1 1) slab with seven atom-layers, C-top, C-center, C-hollow, Si-top, Si-center and Si-hollow interfacial models are established according to their different terminations and stacking sequences. Based on simulated results of interfacial energy, work of adhesion and electron density, the C-top and Si-top models provide the most stable interfacial structures with largest work of adhesion and most stable electronic structure. C-top and Si-top models possess the ultimate tensile strengths of 6.33 and 6.65 GPa, while the tensile strains are separately 10% and 12%. Meanwhile, the tensile interfacial fractures appear in the Al slabs of all six interfacial models. For the C-top and Si-top models, the shear strengths are 5.38 and 5.34 GPa, while the shear strains are 12% and 12% respectively. Moreover, the shear slipping along <1 1¯ 0> directions occur in the Al slabs far from the interface for C-top model and close to the interface for Si-top model. In conclusion, an atomic-scale investigation on interfacial structures and mechanical deformations of β-SiC/Al interfaces can be brought into light for designing, fabricating and processing new ceramic/metal composites.
Interface migration in microstructures is mediated by the motion of line defects with step and dislocation character, i.e., disconnections. We propose a continuum model for arbitrarily-curved grain ...boundaries or heterophase interfaces accounting for disconnections' role in grain rotation. Numerical simulations show that their densities evolve as grain size and shape change, generating stresses and increasing or decreasing misorientation; the predictions agree with molecular dynamics simulations for pure capillarity-driven evolution, and are interpreted through an extended Cahn-Taylor model.
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