Al Slab Research Articles

Assessment of machine learning models trained by molecular dynamics simulations results for inferring ethanol adsorption on an aluminium surface

Molecular dynamics (MD) simulations can reduce our need for experimental tests and provide detailed insight into the chemical reactions and binding kinetics. There are two challenges while dealing with MD simulations: one is the time and length scale limitations, and the latter is efficiently processing the massive amount of data resulting from the MD simulations and generating the proper reaction rates. In this work, we evaluated the use of regression machine learning (ML) methods to solve these two challenges by developing a framework for ethanol adsorption on an Aluminium (Al) slab. This framework comprises three main stages: first, an all-atom molecular dynamics model; second, ML regression models; and third, validation and testing. In stage one, the adsorption of ethanol molecules on the Al surface for various temperatures, velocities and concentrations is simulated using the large-scale atomic/molecular massively parallel simulator (LAMMPS) and ReaxFF. The outcome of stage one is utilised for training, testing, and validating the predictive models in stages two and three. We developed and evaluated 28 different ML models for predicting the number of adsorbed molecules over time, including linear regression, support vector machine (SVM), decision trees, ensemble, Gaussian process regression (GPR), neural network (NN) and Bayesian hyper-parameter optimisation models. Based on the results, the Bayesian-based GPR showed the highest accuracy and the lowest training time. The developed model can predict the number of adsorbed molecules for new cases within seconds, while MD simulations take a few weeks. This adsorption rate can then be used in macroscale simulations to tackle the time and length scale limitations. The proposed numerical framework has the potential to be generalised and, therefore, contribute to future low-cost binding reaction estimations, providing a valuable tool for industry and experimentalists.

The Effects on Stability and Electronic Structure of Si-Segregated θ′/Al Interface Systems in Al-Cu Alloys

This study systematically investigates the energy and electronic properties of Si-segregated θ′(Al2Cu)/Al semi-coherent and coherent interface systems in Al-Cu alloys using ab initio calculations. By evaluating the bonding strength at the interface, it has been revealed that Si segregated at the A1 site (Al slab) of the semi-coherent interface systems exhibits the most negative segregation energy, resulting in a noticeable decrease in total energy and an increase in interface adhesion. The electronic structure analysis indicates the presence of Al-Cu and Al-Al bonds, with Si occupying the A1 site. The strong bond formation between Al-Cu and Al-Al is essential for improving interface bonding strength. The results of the calculating analyses are consistent with the results of the previous experiments, and Si can be used as a synergistic element to reduce the θ′/Al interface energy and further reduce the coarsening drive of the θ′ precipitated phase, which can provide new perspectives and computational ideas for the compositional design of heat-resistant Al-Cu alloys.

Interface enhancement mechanism of rolled Mg/Al clad plate with particle interface control

In this study, the cold-spraying process was utilized to deposit Al particles onto an Al slab, an Mg slab, and both Al and Mg slabs to form an ultra-thin interlayer, and then the clad slabs were rolled at 400 °C, developing three roll-bonding processes: the roll-bonding process with cold-sprayed Al powder on the Al slab (CS-Al), the roll-bonding process with cold-sprayed Al powder on the Mg slab (CS-Mg), and the roll-bonding process with cold-sprayed Al powder on both the Al slab and the Mg slab (CS-Both). The effects of three different cold-sprayed Al particle interlayer processes on the mechanical properties of rolled Mg/Al clad plates were investigated to improve the mechanical properties. The microstructure, texture evolution, intermetallic compound formation, mechanical properties, and mechanisms involved in the Mg/Al clad plate rolling were systematically investigated. The results showed that the pre-bonding between the particles and the substrates through cold-spraying had a significant impact on the bonding strength of the Mg/Al clad plates, and the CS-Both process can increase the average shear strength of the Mg/Al clad plates to 49.24 MPa at a medium reduction rate of 37.5 %, 2.5 times that of the conventional rolling process. The CS-Both process constructed more evident dual microscopic three-dimensional interfaces and promoted more thorough atomic diffusion at the interface through the double-sided cold-spraying process. Meanwhile, the dual cold-sprayed Al coatings on both the Mg slab and Al slab underwent dynamic recrystallization during rolling to form a homogeneous unit with no additional coating interfaces. Fine grain strengthening and dislocation strengthening were judged to be important mechanisms for improving the mechanical performance of the interfacial layer.

The role of sawtooth-shaped nano riblets on nanobubble dynamics and collapse-induced erosion near solid boundary

In this research, surfaces inspired by shark skin were engineered for aluminum (Al) slabs to investigate the influences of riblets on the collapse dynamics of nanobubbles and the resultant erosion on the slab surfaces. These effects were probed through molecular dynamics simulations. Specifically, surfaces with flat profiles as well as those with small and high sawtooth-shaped nano riblets were modelled for analysis. Near the flat surface, due to the absence of riblets, the water nanohammer, with its semi-spherical shape containing water beads under approximately 30 GPa pressure and 5000 K temperature, impulse the Al slab, transferring both temperature and pressure, thereby inducing maximum erosion. Conversely, surfaces containing riblets separate some parts of water vortices, leading to a shorter collapse time of the nanobubble and the creation of a water nanohammer with a smaller volume compared to their values near a flat surface. Moreover, due to the initial impulse of the water nanohammer to the peak of the riblet, the nanohammer splits into two or three inclined shapes. Then, they diagonally impact the main part of the Al slab, resulting in erosion. The decentralization and diagonal impulse of the water nanohammer in the presence of riblets create a lower erosion volume and depth compared to these values on a flat surface. In summary, it can be inferred that riblets can serve as a passive control method for managing erosion, thereby increasing the lifetime of hulls for ships or submarines.

Partition the total energy of Al3Ti to characterize the Al3Ti/Al interface properties: a first-principles study

The geometric model of coplanar reciprocal lattice points (CRLPs) was used to predict the preferred orientation relationships (ORs) between the Al3Ti intermetallic particle and the Al matrix. The calculation result indicates that there exist two preferred ORs, i.e. (001)Al3Ti//(001)Al, [100]Al3Ti//[100]Al and (010)Al3Ti//(010)Al, [100]Al3Ti//[101¯]Al. The periodic models with a specific interface structure and surface slab models on a particular crystallographic plane were proposed to partition the total energy of the Al3Ti compound into its constituent atoms’ energies. The Ti and two kinds of Al atoms (Wyckoff notation 2b and 4d) possess the energy of -119.80325739 Ry, -5.09778518 Ry, and -5.03677683 Ry, respectively. Compared with the Al3Ti total energy of -269.94919247 Ry, the proposed energy partition scheme presents a satisfactory accuracy better than ∼10−7 Ry. Owing to the data of the atom's energy in the solid state, the definite value of surface energy can be obtained whether or not it is a stoichiometric or non-stoichiometric surface. The interface energy calculation, which was carried out on all the preferred ORs with all the possible atomic configurations, indicates that the energy-preferred interface possesses the orientation relationship of (001)Al3Ti//(001)Al, [100]Al3Ti//[100]Al. The atomic configuration is that the atoms on the surface of the Al slab face directly to atoms on the second layer of the Al3Ti slab with the Al-Ti terminated surface on account of its lowest interface energy of 0.005 J/m2. The predicted OR agrees well with the previously published experimental results, and the significantly lower interface energy explains the potency of the Al3Ti particle as a heterogeneous nucleation site in the aluminum solidification process.

Reactive-dynamic characteristics of a nanobubble collapse near a solid boundary using molecular dynamic simulation

In the current research, we studied the collapse mechanism of the nanobubble under mirror and real wall protocols using molecular dynamics simulation. Moreover, we analyzed reactive properties of the real wall during the collapse process. Towards this aim, an aluminum (Al) slab has been considered as a real wall, and its behavior after the formation of a nanojet has been investigated. The obtained results indicated that the dynamics of nanobubble collapse under the mirror and real protocols are similar. The collision between the shock wave and the nanobubble leads to the collapse of nanobubble, and the nanojet was formed during this collapse process. However, the nanobubble can collapse sooner when the Al slab is used as a real wall. Moreover, the surface roughness of the Al slab during the shock propagation and nanobubble collapse was increased due to the formation of the chemical reaction between Al and water under the real wall protocol, while the mirror wall has a roughness-free surface from the beginning to the end. The chemical reaction 2Al + H2O→ AlOH + AlH creates the amorphous layer containing the AlOH and AlH species on the surface of the Al slab. This layer grows semi-smoothly during bubble shrinkage and collapse process, while the growth type was changed to an island shape after the complete collapsing. The island shape on the Al slab was formed behind the nanojet due to the water vortices that are formed after the nanobubble collapse.

Multi-layered shielding materials for high energy space radiation

One of the biggest challenges of the human spaceship in deep space is the harmful space radiation environment. In this paper, we present a multi-layered shielding approach, which reduces the radiation exposures from the trapped radiation, Solar Particle Events (SPE), and Galactic Cosmic Radiation (GCR). We have used shielding materials namely aluminum (Al), Polyethylene (PE), Hydrogen stored boron nitride, Water, Polybenzoxazine, Epoxy, Kevlar, Zylon, Polyetherimide, Polysulfone, Lithium Hydride (LiH), Liquid Methane, and Hydrogenated Graphite Nanofiber (HGNF) respectively. The dose equivalent (DE) for each shielding material is calculated using an On-line Tool for the Assessment of Radiation In Space (OLTARIS) and High Charge and Energy TRaNsport (HZETRN) for 2010 Solar minimum GCR. In addition, the dose equivalent for the first Al slab of 10 g/cm2 followed by a different combination of materials slabs of 90 g/cm2 is analyzed. In multi-layered analysis, we observed that Al + LiH is more effective than remaining shielding materials. In addition, combinations of hydrogen, boron, and nitrogen-rich materials slabs behind the Al slab are studied. In this analysis, the dose equivalent reduction per unit thickness is higher in the first hydrogen-rich material slab of a shield than over any of the other materials slabs. In Sandwich combinations, PE, LiH, Liquid Methane, and Hydrogen stored boron nitride sandwiched between Al. Al + LiH + Al showed better performance. In addition, the dose equivalent was compared between OLTARIS and HZETRN transport codes.

Melting at Mg/Al interface in Mg–Al–Mg nanolayer by molecular dynamics simulations

The melting at the magnesium/aluminum (Mg/Al) interface is an essential step during the fabrications of Mg–Al structural materials and biomaterials. We carried out molecular dynamics simulations on the melting at the Mg/Al interface in a Mg–Al–Mg nanolayer via analyzing the changes of average atomic potential energy, Lindemann index, heat capacity, atomic density distribution and radial distribution function with temperature. The melting temperatures () of the nanolayer and the slabs near the interface are significantly sensitive to the heating rate () over the range of ≤ 4.0 K ps−1. The distance () range in which the interface affects the melting of the slabs is predicted to be (−98.2, 89.9) Å at if the interface is put at = 0 and Mg (Al) is located at the left (right) side of the interface. The of the Mg (Al) slab just near the interface (e.g. Å) is predicted to be 926.8 K (926.6 K) at with 36.9 K (37.1 K) below 963.7 K for the nanolayer. These results highlight the importance of regional research on the melting at an interface in the nanolayers consisting of two different metals.

First-principles investigation on stability and electronic structure of Sc-doped θ′/Al interface in Al−Cu alloys

The properties of Sc-doped θ′ (Al2Cu)/Al interface in Al−Cu alloys were investigated by first-principles calculations. Sc-doped semi-coherent and coherent θ′ (Al2Cu)/Al interfaces (Sc doped in Al slab (S1 site), Sc doped in θ′ slab (S2 site)) were modeled based on calculated results and reported experiments. Through the analysis of interfacial bonding strength, it is revealed that the doping of Sc at S1 site can significantly decrease the interface energy and increase the work of adhesion. In particular, the doped coherent interface with Sc at S1 site which is occupied by interstitial Cu atoms has very good bonding strength. The electronic structure shows the strong Al—Cu bonds at the interfaces with Sc at S1 site, and the Al—Al bonds at the interfaces with Sc at S2 site are formed. The formation of strong Al—Cu and Al—Al bonds plays an important role in the enhancement of doped interface strength.

Revealing the Al/L12-Al3Zr inter-facial properties: Insights from first-principles calculations

To uncover the mechanical performance and micro-structure of Al/L12-Al3Zr interface through density functional theory, four interface models are investigated considering two different terminations of L12-Al3Zr surfaces along the [001] direction. Results indicated stacking sequence and atom type between two phases influences the mechanical performance of the interface quite well. The interface consisting of four Al atom-terminated Al(001) slab as well as one Al and four Zr atom-terminated L12-Al3Zr(001) slab not only has relatively even charge distribution due to the same atomic arrangement as L12-Al3Zr bulk, but also enjoys the strong hybrid bonds between inter-facial Al and Zr atoms, gaining the best performer in the tensile test. However, it's the different situation for the model constructed by four Al-terminated Al(001) slab and four Al-terminated L12-Al3Zr(001) slab, the poorest performer. As for the other two interface models with the similar fracture energy and peak stress, one of them, though held together just through the relatively weak bonds of inter-facial Al, has the advantage of evenly-located inter-facial atoms which results in the even charge distribution, for the same atomic arrangement as Al bulk. The other, the inter-facial atoms of which are distributed unevenly, gets the benefit of the strong hybridization of inter-facial atoms.

First-principles calculations on the adhesion strength, fracture mechanism, interfacial bonding of the semi-coherent Al(1 1 1)/Al3BC(0001) interfaces

In this work, we have systematically explored the atomic structure, adhesion work, interfacial energy and fracture mechanism of the semi-coherent Al(111)/Al3BC(0001) interface using the first-principles calculations. The relaxed atomic structure reveals that the MT configurations are unstable and moves to HCP1 and HCP2 configurations. Furthermore, the obtained adhesion works and interfacial energies relaxed that the B-terminated Al(111)/Al3BC(0001) interface of HCP2 configurations has the highest adhesion work and the lowest interfacial energy, indicating that the HCP2-B interface is the most stable. The electronic structure of the B-terminated Al(111)/Al3BC(0001) interface shows that there are Al-B covalent bonds formed at the interface. For the B-HCP2 interface, due to the formation of strong Al-B covalent bonds at the interface, mechanical failure eventually occurs in the Al slab.

Measurement of leakage neutron spectra for aluminium with D-T fusion neutrons and validation of evaluated nuclear data

In the integral benchmark experiment presented here, an aluminium (Al) slab sample (300 mm × 300 mm × 100 mm) was irradiated with Deuterium-Tritium (D-T) fusion neutrons. The neutrons leaking from the sample were detected by a BC501A organic liquid scintillator through the time-of-flight (TOF) method; the neutron energy spectra were derived from the as-obtained TOF curves by considering the detector efficiency. For comparison, some leakage neutron spectra were also simulated by combining a Monte Carlo neutron transport code with evaluated nuclear data from the ENDF/B-VIII.0, JENDL-4.0 and CENDL-3.1 libraries. All the calculated values agreed with the experimental data within 10%, except for a few energy ranges. The values predicted using the ENDF/B-VIII.0 library were lower and higher than the measured ones at below and higher above 4 MeV, respectively; the data based on the CENDL-3.1 and JEDNL-4.0 libraries exhibited some larger differences in the 9.5–12 MeV range at 120∘. The possible causes of these discrepancies are also discussed.

Development of radiative opacity code OPIND for high energy density plasma and its application in radiation hydrodynamics

We developed the program OPIND to generate opacity data for use in radiation hydrodynamics simulations. This is an extension of our earlier work on opacity of elemental plasma based on average atom model [1]. In this work, we extended the capability of OPIND to treat mixture plasmas which employs the ideal gas mixing rule to obtain partial densities. Screened hydrogenic model was employed to obtain radiative properties and hence total opacity. Extensive validation for average ionization and Rosseland mean opacity of C, Al, Fe, Ge, Xe and Au plasmas were performed. OPIND was then employed to study the opacity of CH and Au-Gd mixture plasmas. The role of pressure ionization on CH opacity as well as opacity enhancement in Au-Gd plasma due to the presence of Gd were investigated. Further validation of OPIND was done by performing 1D radiation hydrodynamics simulations to study the ablation in Al slab subjected to radiation temperature drives. We studied the shock trajectory, mass ablation rate and evolution of thermodynamic parameters during shock propagation in Al slab. The scaling law for radiation temperature as a function of shock speed for strong shocks was also verified. We observed good agreement of data generated in our simulations with reported experimental and simulation data. Equation of state data were generated using the SBCRIS library developed by us.

Strain hardening and embrittlement of Al crystal with a surface oxidized void

Although metal failure has been extensively investigated, the impact of oxidation on the failure of ductile metals involving defects is relatively unclear. In this study, reactive molecular dynamics simulations are performed to observe the change in the mechanical properties (e.g., strength and ductility) of a voided Al crystal when the void surface is oxidized. For a preoxidized void surface, as the oxide scale becomes thicker and denser, the microdeformation and fracture mechanisms of the Al crystal change significantly, according to which four failure modes can be identified. Furthermore, the decrease in the fracture strain indicates a transition from significant plasticity to brittle fracture of the Al slab. A simple analytical model is proposed to establish the relation between the yield strength and oxygen uptake. When the void surface oxidation continuously occurs while loading, the continuous supply of oxygen heals the oxide/metal interface, leading to a considerably enhanced ductility and the occurrence of a unique strain hardening phenomenon. The presented findings highlight the influence of the interaction between the chemical and mechanical effects on the deformation and fracture mechanisms of metallic materials.

Observation of gain coefficients of 15.47 nm Li-like Al soft x-ray laser in a recombining plasma pumped by a compact YAG laser

A Li-like Al soft x-ray laser oscillation (15.47 nm) by means of recombination plasma scheme was investigated to enhance the gain coefficent of lasing medium. In this study, we employed a Nd:YAG laser pulse composed of 8-pulse train, in which each pulse width was 400 ps and its interpulse time was 400 ps. The laser beam was tightly line-focused into 50 μm in height and 12 mm in length on Al slab target by using prism lens array. The created cylindrical plasma showed that with increasing plasma length the lasing intensity at 15.47 nm increased expoentially up to 3.5 mm. For the laser energy of 3 J, the gain coefficient was 8.3 cm−1. Above 3.5 mm in length, the signals seemed to increase linearly, indicating that the lasing action reached the saturation regime.

First-principle calculations on the Al/L12-Al3Zr heterogeneous nucleation interface

The interfacial properties including interfacial energy, work of adhesion and electronic structure of Al(100)/Al3Zr(100) were calculated by first-principle calculations based on the density functional theory. The seven layered Al(100) slab and nine layered Al3Zr(100) slab were employed to construct the interface models. And six Al(100)/Al3Zr(100) interfaces, including Top, Bridge and Center sites for the Al- and AlZr- terminations, were considered to study. The interfaces with center site stacking of both terminations are the most stable as they have the largest adhesion work (Wad). The interfacial bonding characteristics is a combination of covalent and metallic bond for the AlZr-terminated center site interface, but only metallic for the Al-terminated center one. Under the whole range of μZrslab−μZrbulk, the interfacial energy of AlZr-terminated center interface is negative, which is much smaller than that of α-Al and its melt (0.15J/m2), indicating that Al3Zr particle is an effective nucleant for α-Al primary grains.

First-principles investigation of interfacial stability, mechanical behavior and failure mechanism of β-SiC(1 1 1)/Al(1 1 1) interfaces

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.

Engineering the structural, optical and dielectric properties of ZnSe thin films via aluminum nanosandwiching

In this work, two stacked layers of ZnSe thin films are nanosandwiched with aluminum slabs of variable thickness in the range of 10–100 nm. The films which are studied by the X-ray diffraction and ultra-violet visible light spectroscopy techniques exhibit interesting features presented by extension of the cubic lattice parameter, increase in the grain size and reduction in both of the microstrains and defect density. The Al nanosandwiching successfully engineered the energy band gap through narrowing it from 2.84 to 1.85 eV. In addition, the Al nanosandwiching is observed to form interbands that widens upon increasing the Al layer thickness. It also changed the electronic transition nature from direct allowed to direct forbidden type. Moreover, remarkable enhancement in the light absorbability by 796 times is observed near 1.72 eV for two stacked ZnSe layers nanosandwiched with Al slab of thickness of 100 nm. The dielectric constant is also increased three times and the dielectric tunability vary in the range of 3.0-1.2 eV. The nonlinearity in the dielectric spectra and the engineering of the band gap that become more pronounced in the presence of Al slabs make the ZnSe more attractive for nonlinear optical applications.

Ab initio approach to lattice softening of an Al slab driven by collective electronic excitations after ultrashort laser pulse irradiation

Recent advances in ultrashort laser pulse techniques have opened up a wide variety of applications in both fundamental physics and industrial fields. In this work, $ab$ $initio$ molecular dynamics simulations based on time-dependent density functional theory revealed a steady deceleration of lattice distortion propagation in an aluminum slab with increasing laser pulse intensity. Analysis of the interatomic force revealed a significant reduction in the harmonic terms and non-monotonic growth of anharmonicity. This behavior was characterized by spatially non-uniform force screening by plasmons, which is missing from Born--Oppenheimer molecular dynamics, and is consistent with the current interpretation of laser-induced periodic structure patterning. This work provides a semi-quantitative criterion for modifying the phonon properties of non-equilibrium systems.

Adsorption of ethanol molecules on the Al (1 1 1) surface: a molecular dynamic study.

The adsorption process of ethanol molecules on Al slabs was investigated by molecular dynamic simulations with a ReaxFF force field. The force field used in this paper has been validated by comparing adsorption energy results with quantum mechanical (QM) calculations. All simulations were performed under the canonical (NVT) ensemble. The single-molecule adsorption simulation shows that the hydroxyl group plays a more important role in the whole progress than the ethyl group. Besides, decomposition of hydroxyl groups was also observed during multimolecule adsorption processes. Simulations of adsorption processes of Al slab by ethanol molecules at different temperatures and pressures (controlled by the number of ethanol molecules) was also performed. System energy and radial distribution function (RDF) plots were invoked to describe adsorption processes and centro-symmetry parameter (CSP) analysis was adopted to study the surface properties with coating layers. Our results indicate that the whole adsorption process can be divided into two periods and the greater the pressure, the more ethanol molecules diffuse into the Al slab. How raising the temperature helps the adsorption processes is related to the initial number of molecules. The crystal structure of the Al surface will become amorphous under the constant impact of ethanol molecules.