Si Network Research Articles

Microstructure evolution of AlSi10Mg alloy in RAP process

Abstract With its computer-aided layer-by-layer production approach, additive manufacturing (AM) and powder bed laser fusion (PBLF) paved the way to produce metallic parts more precisely than any other manufacturing technique. However, the combinability and the interaction of this relatively new manufacturing technique with the other near-net shape production techniques is still a mystery. In this study, the recrystallization and partial melting (RAP) behavior, which is a feedstock production approach for semisolid forming methods, investigated on AlSi10Mg parts produced by PBLF and conventional casting were compared in terms of microstructural and hardness evaluations. After the reheating process, the globalization of Si particles and the breakdown of the Si network around the melt pools were displayed with light microscope and scanning electron microscope (SEM) images. The hardness values of the PBLF as-fabricated specimens were found to be significantly higher than the as-cast specimens; however, the values were almost equaled after the RAP treatment and even got lower on the bottom and top regions of the PBLF samples after 20 min of reheating because of the enlarged shrinkage porosities and the coarsened morphology.

Dynamic analysis of a novel SI network rumour propagation model with self-regulatory mechanism

Dynamic analysis of a novel SI network rumour propagation model with self-regulatory mechanism

New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low- and high-metallicity values

Context. Among the silicon-bearing species discovered in the interstellar medium, SiS and SiO stand out as key tracers due to their distinct chemistry and variable abundances in interstellar and circumstellar environments. Nevertheless, while the origins of SiO are well documented, the SiS chemistry remains relatively unexplored. Aims. Our objective is to enhance the network of Si- and S-bearing chemical reactions for a gas-grain model in molecular clouds, encompassing both low and high metallicities. To achieve this, we calculated the energies and rate coefficients for six neutral atom-diatom reactions involved in the SiCS triatomic system, with a special focus on the C+SiS and S+SiC collisions. Methods. We employed the coupled-cluster method with single and double substitutions and a perturbative treatment of triple substitutions (CCSD(T)) refined at the explicitly correlated CCSD(T)-F12 level. With these computational results in conjunction with supplementary data from the literature, we construct an extended network of neutral-neutral chemical reactions involving Si- and S-bearing molecules. To assess the impact of these chemical reactions, we performed time-dependent models employing the Nautilus gas-grain code, setting the gas temperature to 10 K and the H2 density to 2 × 104 cm−3. The models considered two initial abundance scenarios, corresponding to low- and high-metallicity levels. Abundances were computed using both the default chemical network and the constrained network, enriched with newly calculated reactions. Results. The temperature dependence for the reactions involving SiS were modelled to the k(T) = α (T/300)β exp (−γ/T) expression, and the coefficients are provided for the first time. The high-metallicity models significantly boost the SiS production, resulting in abundances nearly four orders of magnitude higher compared to low-metallicity models. Higher initial abundances of C, S, and Si, roughly ~2, 190, and 210 times higher, respectively, contribute to this. Around the age of 103 yr, destruction mechanisms become relevant, impacting the abundance of SiS. The proposed production reaction S + SiC → C + SiS, mitigates these effects in later stages. By expanding the gas reaction network using a high-metallicity model, we derived estimates for the abundances of observed interstellar molecules, including SiO, SO, and SO2. Conclusions. We demonstrate the significance of both SiC+S and C+SiS channels in the SiS chemistry. Notably, the inclusion of neutral-neutral mechanisms, particularly via Si+HS and S+SiC channels, played a pivotal role in determining SiS abundance. These mechanisms carry a significance level on a par with that of the well-known and fast ion-neutral reactions.

Facile synthesis of dense SiBCN coatings with excellent compactness, smoothness, and high-temperature inertness on defective graphite surfaces

SiBCN ceramics possess extreme high-temperature stability among engineering ceramics; however, their application is constrained by the difficulty in achieving large continuous products at low cost. This work exhibits the possibility of fabricating SiBCN continuous coatings on graphite substrates to improve their surface integrity, hardness, and inertness. The ceramic coatings were fabricated simply by spin coating, curing, and pyrolysis. The key innovations are the synthesis of the precursor, polyborosilazane (PBSZ), that derives continuous ceramic films after pyrolysis, and the finding that the xylene solution of PBSZ can achieve a very good spinning performance on various surfaces, especially the low-quality graphite surfaces with holes. The fabricated SiBCN coatings, characterized to be networks of Si–C, Si–N, C–C, and B–N bonds, possessed smooth and hard surfaces with roughness below 9 nm and a hardness of 7.3 GPa. The coating thickness can be well controlled in the range of 1.4 – 2.1 μm as the latter is linearly dependent on the concentration of PBSZ in the solution. Detailed observations of surface morphologies and physisorption experiments reveal that the coating surfaces are crack-free and highly dense, rendering a significant reduction in specific surface areas when a defective graphite face is coated.

Temperature-dependent water corrosion mechanism of silicon carbide: Atomic insights from reactive molecular dynamics simulation

Silicon carbide (SiC) is an ideal material for both aeronautics and space industries, but SiC is highly susceptible to water corrosion at high temperature. A clear understanding of water corrosion mechanism of SiC is still lacking because the complex interaction dynamics are extremely difficult to be investigated experimentally. In this study, the temperature-dependent of water corrosion mechanism of SiC was investigated by reactive molecular dynamics simulation, and three different corrosion regimes were observed with the increase of the ambient temperature. In regime I (below 1000 K), only Si–H and Si–OH terminations were formed on SiC surface and almost no corrosion occurred; in regime II (1000–1500 K), the same number of carbon and silicon atoms were corroded in the form of gaseous molecules, and the relation between the number of atoms lost and temperature was in good agreement with the Arrhenius expectation; lastly, in regime III (above 1500 K), the number of Si–O–Si groups formed exceeded the volatilized number, leading to the obvious retention of the Si–O–Si network structures. These results can guide the design and preparation of SiC materials for aerospace applications by providing an atomic insight into the mechanisms of water corrosion on SiC.

Influence of structural characteristics of a Si nanoparticulate anode on all-solid-state Li-ion batteries

Si nanoparticles with independently controlled size and oxygen content have been produced by plasma spraying physical vapor deposition followed by the retarded oxidation. These nanoparticles are used as the negative electrode of all-solid-state batteries with sulfide solid electrolyte, and the influence of size and oxygen content on battery performance has been analyzed. The cells containing Si nanoparticles smaller than 150 nm with the oxygen content x in SiO x smaller than 0.1 have attained relatively high capacity and a good stable cyclability simultaneously after 50 cycles. This could be due to the formation of unique and uniform synaptic-like Si network with small Si nanoparticles within the electrode maintaining a firm contact with the Cu foil, which contrasts to large lateral crack formation for the cell with large Si particles.

Microstructure and compression performance of novel AlSi10Mg composite auxetic structures fabricated by additive manufacturing

In order to further increase the mechanical properties of auxetic structures, a novel enhanced composite (NEC) auxetic structure was proposed and characterized by the combination of the enhanced re-entrant anti-trichiral and double arrow structures. The NEC structures were fabricated from AlSi10Mg powders through selective laser melting (SLM) additive manufacturing technology. The grain morphology and microstructure characteristic of the AlSi10Mg sample were comprehensively analyzed. Results indicate that both columnar and equiaxed grains can be observed in the SLM-fabricated sample. Columnar grains with the size around 52 μm are mainly distributed in the melt pool and equiaxed grains exist at the boundary of the melt pool. The columnar grains are approximately perpendicular to the boundary of the melt pool and grow towards the center of the melt pool, exhibiting <100> filamentous texture. The melt pool boundaries can be divided into three distinct regions, i.e., coarse grain zone, fine grain zone, and heat affected zone. The microstructure of the as-built sample consists of elongate cellular α-Al matrix decorated with eutectic Si network boundaries. The mechanical properties and energy absorption performance are systematically investigated by means of Finite Element Analysis (FEA) verified by the experimental results. It is found that the elastic modulus, compression strength, Poisson's ration and energy absorption of the NEC structures are sensitive to the structure parameters. i.e., the compression stress and energy absorption present an increasing trend with the increasing of α, decreasing of l1 and β, while l1, α and β exhibit opposite effect on the Poisson's ratio. Moreover, the rotational combination of varied structures can lead to an excellent energy absorption capacity of the NEC structures, which is significantly higher than that of other auxetic structures. The results will provide guidance for the structure design of lightweight auxetic structures with enhanced performance and outstanding auxeticity.

Effect of Tri-Metallic Micro-galvanic Corrosion on Localized Corrosion Based on Numerical Simulation: Geometric Effect of Intermetallic Compounds

ABSTRACT This study investigated the corrosion behavior of ADC12 and A365 aluminum alloys for automotive parts in the context of the growing use of aluminum parts in electric vehicles. Only ADC12 exhibited the formation of Al(OH)3 particle layer after corrosion, which was attributed to the micro-galvanic effect influenced by the geometry characteristics of its microstructure. Results revealed that ADC12 was prone to the formation of Al(OH)3 particle layers due to the geometric effects of Si and θ-Al2Cu, which facilitates the isolation of α-Al. The distribution of band-shaped galvanic currents, concentrated in a small α-Al matrix region, was primarily governed by the geometry of Si, creating a preferred structure for α-Al isolation. Additionally, the geometry of θ-Al2Cu contributed to a significant increase in electrochemical kinetics, particularly at the tri-metallic coupled region, further enhancing the susceptibility of the isolation. As a result, the formation of the Al(OH)3 particle layer was attributed to the corrosion of isolated α-Al particles, generated through the synergistic effect of micro-galvanic corrosion. Moreover, the corrosion attack progressed along the eutectic Si network, accompanied by θ-Al2Cu. Overall, the corrosion mechanism of ADC12 and A365 alloy was proposed.

Synthesis and Properties of Moisture‐Crosslinkable Poly(Urethane‐Urea) With Intrinsic Flame Retardancy

To improve the deteriorated performance caused by CO2 release during the curing process of traditional moisture‐crosslinked polyurethane or polyurea and poor flame retardancy, this work realized an effective in situ crosslinking technique triggered by moisture for poly(urethane‐urea) with intrinsic flame retardancy, through the incorporation of trimethoxysilane and phosphorus groups via a continuous two‐stage process. Moisture‐triggered crosslinking reaction of trimethoxysilane groups resulted in the establishment of a robust Si─O─Si network, as confirmed by Fourier transform infrared spectroscopy (FTIR) test. The structure transformation considerably enhanced the material’s strength, with the stress at break increasing from 1.0 to 3.2 MPa and modulus from 32.9 to 46.9 MPa. The flame retardant properties of PUUS1 (poly(urethane‐urea) sample) were investigated through limiting oxygen index (LOI) and cone calorimeter (CCT) analysis, demonstrating satisfactory flame resistance, as evidenced by high LOI value of 29%, high char yield of 46.2%, and controlled smoke production. Combining thermogravimetric analysis‐infrared spectrometry (TG‐IR), X‐ray photoelectron spectroscopy (XPS), and flame retardant performance, it is speculated that the generation of phosphorus‐free radical scavengers in gas phase from diethyl bis(2‐hydroxyethyl) aminomethyl phosphonate (DBHAP), coupled with the barrier effects of charred layer and distinctive Si─O─Si framework in condensed phase inhibited combustion and toxic gas emission. The results highlight the successful synthesis of a moisture‐crosslinkable poly(urethane‐urea) with intrinsic flame retardancy, promising for applications necessitating moisture‐crosslinkable materials with superior flame resistance.

Constructing solidification microstructure selection map for AlSi10Mg alloy processed by laser powder bed fusion

The cellular structures, which consist of cells and eutectic networks at the cell boundaries, determine the mechanical properties of the Al–Si alloys fabricated by laser powder bed fusion (L-PBF). Therefore, it is scientifically interesting and technologically important to establish the relationship between cellular structures and processing parameters, which is applicable to all kinds of processing methods involving rapid directional solidification, such as L-PBF. In this work, a rapid solidification microstructure selection map (SMSM) of the Al–10Si system in temperature gradient (G)–solidification velocity (V) space is constructed by a synergistic calculation with dendritic and eutectic growth models compatible to the L-PBF process. Considering that the divorced eutectic reaction should occur as the width of the liquid film entrapped in the α-Al cell boundaries becomes smaller than the Al–Si eutectic spacing, the G–V domain suitable for acquiring the cellular structures decorated with divorced eutectic Si networks is determined on the SMSM. The microstructure evolution trends predicted by the SMSM are well consistent with those in the L-PBFed AlSi10Mg melt pools with different processing parameters. The length scales of actual microstructures observed by the experiments from this work and the literature are quantitatively compared to those estimated by the SMSM, and the experimental results are basically in accord with the SMSM. It is demonstrated that divorced eutectic Si networks prefer to form at the bottom of the melt pool, where G is large (> 5 × 106 K/m) and V is small (3 × 10−4–6 × 10−3 m/s) in the SMSM. The outcomes of this work may provide fundamental guidance for tailoring the microstructures of the L-PBFed Al–Si alloys for achieving optimal mechanical properties.

Numerical study on the effect of crystallographic orientation on mechanical behavior and its anisotropy of laser powder bed fusion AlSi10Mg

Anisotropic strength and ductility are limiting factors for the application of laser powder bed fusion AlSi10Mg. Previous efforts were devoted to explaining the origins of anisotropy mainly from the geometrical orientations of the Al-Si cellular structure and melt pool border, but the effect of crystallographic orientation is still unexplored. The present work aims to assess the mechanical behavior of Al-Si cellular structure using crystal plasticity model, with a focus on how grain orientation affects strength, damage initiation and their anisotropy. Forty-four crystallographic orientations were generated and assigned to a representative volume element resembling the real Al-Si cellular structure. For each orientation, simulations of uniaxial tension along the building direction and the perpendicular direction were performed. It is found that the grain orientation has a huge influence on both strength and damage sensitivity. Nevertheless, the correlation between strength and orientation cannot be established with the Schmid or Taylor factors due to the influence of the elongated Si network. Comparing the results for the two loading directions, strength anisotropy is revealed to present a weak dependence on grain orientation, whereas damage anisotropy varies significantly in the orientation space. The findings of this work can be used for up-scale modeling of mechanical behavior of additively manufactured AlSi10Mg.

Persistent Homology Analysis of the Microstructure of Laser-Powder-Bed-Fused Al-12Si Alloy.

The laser powder bed fusion (L-PBF) process provides the cellular microstructure (primary α phase surrounded by a eutectic Si network) inside hypo-eutectic Al-Si alloys. The microstructure changes to the particle-dispersed microstructure with heat treatments at around 500 °C. The microstructural change leads to a significant reduction in the tensile strength. However, the microstructural descriptors representing the cellular and particle-dispersed microstructures have not been established, resulting in difficulty in terms of discussion regarding the structure-property relationship. In this study, an attempt was made to analyze the microstructure in L-PBF-built and subsequently heat-treated Al-12Si (mass%) alloys using the persistent homology, which can analyze the spatial distributions and connections of secondary phases. The zero-dimensional persistent homology revealed that the spacing between adjacent Si particles was independent of Si particle size in the as-built alloy, whereas fewer Si particles existed near large Si particles in the heat-treated alloy. Furthermore, the first principal component of a one-dimensional persistent homology diagram would represent the microstructural characteristics from cellular to particle-dispersed morphology. These microstructural descriptors were strongly correlated with the tensile and yield strengths. This study provides a new insight into the microstructural indices describing unique microstructures in L-PBF-built alloys.

Optimizing the Solution Annealing of Additively Manufactured AlSi10Mg

Abstract Laser-based powder bed fusion of metals exhibit process-induced anisotropy and residual stresses, making post-manufacturing heat treatment occasionally beneficial. For AlSi10Mg, a T6 heat treatment (solution annealing, quenching, artificial aging) is recommended. Nevertheless, mechanical strength decreases as (1) the eutectic Si network dissolves, (2) the amount of dissolved Si in the Al grains decreases, and (3) the size of the silicon particles and aluminum crystals increases during solution annealing. This changes the mechanical characteristics directly or by influencing the formation of precipitation during the aging process. The success of solution annealing is affected by the annealing duration and the part’s temperature at the moment of quenching. Short annealing durations dissolve a sufficient amount of Si and Mg in the Al matrix. Therefore, both the annealing temperature’s holding duration and the heating process significantly impact the resulting microstructure. In this study, samples of different shape and size where subjected to a T6 heat treatment with different solution annealing temperatures and durations. The influence on mechanical properties after quenching and aging was investigated by hardness and tensile tests. Maximum strength is achieved by quenching promptly upon reaching the solution annealing temperature, while longer durations reduce strength as explained by the Larson-Miller parameter.

Influence of Ni Contents on Microstructure and Mechanical Performance of AlSi10Mg Alloy by Selective Laser Melting.

To improve the tensile strength and wear resistance of AlSi10Mg alloys, a novel in situ synthesis method of selective laser melting (SLM) was used to fabricate the Ni-reinforced AlSi10Mg samples. The eutectic Si networks formed around the α-Al crystals by diffusion and transportation via Marangoni convection in the SLM process. Moreover, the XRD and TEM results verified that the Al3Ni nanoparticles were created by the in situ reaction of the Ni and aluminum matrix in the Ni/AlSi10Mg samples. Therefore, the microstructure of the Ni-containing alloys was constituted by the α-Al + Si network + Al3Ni phases. The dislocations accumulated at the continuous Si network boundaries and cannot transmit across the dislocation walls inside the Si network. SEM results revealed that the continuity and size of eutectic Si networks can be tailored by adjusting the Ni contents. Furthermore, the Al matrix also benefited from the Al3Ni nanoparticles against the dislocation movement due to their excellent interfacial bonding. The 3Ni-AlSi10Mg sample exhibited high mechanical properties due to the continuous Si networks and Al3Ni nanoparticles. The tensile strength, elongation, Vickers hardness, friction coefficient, and wear volumes of the 3Ni-AlSi10Mg samples were 401.15 ± 7.97 MPa, 6.23 ± 0.252%, 144.06 ± 0.81 HV, 0.608, 0.11 mm3, respectively, which outperformed the pure AlSi10Mg samples (372.05 ± 1.64 MPa, 5.84 ± 0.269%, 123.22 ± 1.18 HV, 0.66, and 0.135 mm3).

Evolution of multi-cellular structure on Zr and Er modified Al6Si1Mg alloy fabricated by laser powder bed fusion

The printability of Al6SiMg0·5Er1·0Zr alloy at various laser power, scan speed, and hatch spacing was investigated. The optimal processing window was determined. The relationship between hatch spacing and lack of fusion (LOF) defects and microstructure is discussed. Hatch spacing significantly affects the cellular size, which is formed by eutectic Si network, and medium hatch spacing can achieve the finest microstructure. Samples with high densities and fine microstructures were investigated more carefully. The grain and cellular boundaries have many Al3(Er,Zr) phases. The grain size was refined to 2.64 μm, and the epitaxial growth of columnar crystals was completely suppressed. The cellular structure has been significantly improved. Get the equiaxed - ultrafine equiaxed - columnar multi-cellular structure with dramatically enhanced mechanical properties. The yield strength, tensile strength, and elongation were 373 Mpa, 480 MPa, and 5.5%, respectively. Grain boundary strengthening and Orowan strengthening was the main strengthening mechanisms.

Flexible All-Inorganic Perovskite Photodetector with a Combined Soft-Hard Layer Produced by Ligand Cross-Linking.

Although perovskite nanocrystals have attracted considerable interests as emerging semiconductors in optoelectronic devices, design and fabrication of a deformable structure with high stability and flexibility while meeting the charge transport requirements remain a huge challenge. Herein, a combined soft-hard strategy is demonstrated to fabricate intrinsically flexible all-inorganic perovskite layers for photodetection via ligand cross-linking. Perfluorodecyltrichlorosilane (FDTS) is employed as the capping ligand and passivating agent bound to the CsPbBr3 surface via Pb-F and Br-F interactions. The SiCl head groups of FDTS are hydrolyzed to produce SiOH groups which subsequently condense to form the SiOSi network. The CsPbBr3 @FDTS nanocrystals (NCs) are monodispersed cubes with an average particle size of 13.03nm and exhibit excellent optical stability. Furthermore, the residual hydroxyl groups on the surface of the CsPbBr3 @FDTS render the NCs tightly packed and cross-linked to each other to form a dense and elastic CsPbBr3 @FDTS film with soft and hard components. The photodetector based on the flexible CsPbBr3 @FDTS film exhibits outstanding mechanical flexibility and robust stability after 5000 bending cycles.

On microstructure and work hardening behavior of laser powder bed fused Al-Cu-Mg-Ag-TiB2 and AlSi10Mg alloys

In this paper, we investigate the correlation between microstructure and mechanical properties, including work hardening rates of two aluminum alloys, Al-Cu-Mg-Ag-TiB2 (A205) and AlSi10Mg, both additively manufactured using laser powder-bed fusion (LPBF) technique. Solutionizing followed by over-aging (T7) and artificial aging (T6) heat treatments were performed on as-built specimens of A205 and AlSi10Mg alloys, respectively, to investigate and compare the evolution of microstructure and tensile properties. Tensile tests based on ASTM E8/E8M standard were performed systematically on both materials in both as-built and heat-treated conditions. High-magnification microstructural characterizations including scanning electron and transmission electron microscopies and electron backscattered diffraction were performed to identify the microstructure-property correlations. The A205 alloy contains an ultrafine uniform equiaxed grain structure with no cell and/or epitaxial growth structure. However, the AlSi10Mg contains a cellular microstructure of primary α‐Al cells surrounded by a continuous cellular Si network. Tensile results on A205 (as-built) revealed discontinuous yielding, while the A205 (T7 HT) material serrated plastic flow instability. T7 heat treatment resulted in a 42.4% and 38% increase in yield stress (YS) and ultimate tensile strength (UTS), respectively, and elongation decreased from 12.5% to 9.5% consequently. However, considerable grain growth, coarsening of Si particles, and dissolution of some Mg2Si phases through solutionizing and T6 aging on AlSi10Mg resulted in increased elongation (5.49–14.20%) and decreased YS and UTS (14.5% and 19.4% respectively). The effect of distinct microstructural features of A205 and AlSi10Mg in as-built condition and their evolution in opposite directions upon aging (in terms of mechanical properties) is reflected in their work-hardening behavior. Considerably higher work hardening of AlSi10Mg alloy in both as-built and aged conditions compared to A205 is linked with the cellular structure containing hard eutectic-Si particles at the cell boundaries.

Zwitterionic polymer coating on medical sponges via a silane coupling agent for inhibiting bacterial and fibroblast adhesion

Medical sponges are widely used in wound management, however the adhesion of bacterial or wound tissue to them may cause infection or secondary damage to patients. In this work, anti-bioadhesive polyvinyl alcohol-formaldehyde sponges with zwitterionic coating were prepared by the dip-coating process using the reactive zwitterionic phosphorylcholineated polyvinylamine (PVAm-PC) and commercial silane coupling agent KH560 at different mass ratios, and their structure, physicochemical, biocompatible and anti-bioadhesive properties were investigated. As compared to pristine sponges, the PVAm-PC-KH560 (PPK) modified sponges with the interconnected pore structure had almost unchanged water vapor transmission rate but decreased swelling degree to a certain extent possibly due to the formation of rigid Si–O–Si networks in the sponges. In vitro biological evaluation confirmed that PVAm-PC-KH560 modified sponges were not cytotoxic and had good resistance to bacteria adhesion with only ∼16% and ∼11% relative bacterial adhesion rate for E. coli and S. aureus respectively. And the optimized PPK-2 sponge showed the best comprehensive bacterial adhesion inhibition properties. Further adhesion assay of L929 fibroblasts showed that PPK-2 sponge could significantly reduce the adhesion of L929 fibroblasts. The results strongly suggested that dip-coating with zwitterionic PVAm-PC and KH560 may provide a promising and facile method to construct an anti-bioadhesive surface for biomedical applications.

Influence of Microstructure on Fracture Mechanisms of the Heat-Treated AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion.

Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.

Toward Atomistic Understanding of Materials with the Conversion–Alloying Mechanism in Li-Ion Batteries

The need for practical anodes for rechargeable batteries calls for new materials with improved storage capacity and cycling stability compared to the materials of today. Materials capable of alloying with alkali metals have been long viewed as a promising pathway to address this challenge. Meanwhile, severe drawbacks associated with the use of such materials led to the development of suitable alternatives, in which governing the reaction mechanism in a battery combines conversion and alloying reactions. These materials feature a high storage capacity and long-term stability during electrochemical cycling. However, the development of these materials is impeded by a lack of fundamental structural understanding due to the complexity of the chemical transformations taking place during battery cycling. Furthermore, amorphization, which is prevalent in these materials, also severely limits the conventional methods of characterization. In the present work, we propose a computational methodology for understanding the structure and reaction mechanism of these conversion–alloying materials by using amorphous substoichiometric silicon nitride as a model system. The developed ReaxFF parameter set allowed exploring the atomistic structure of this material and verify the resulting models through a comparison of calculated and experimentally obtained pair distribution functions (PDFs). The developed methodology also allowed exploring the structural changes occurring during lithiation and delithiation, i.e., operation mechanism in a battery. The analysis of the atomistic structure demonstrates that initial lithiation results in the formation of a Si network, which later participates in further lithiation process. Delithiation also influences the evolution of the amorphous Si network facilitating separation of nitrogen-rich and Si-rich regions and, therefore, confirming the conversion mechanism proposed earlier. Furthermore, the proposed approach allows modeling not only changes at the atomistic scale but also predicting the experimental PDF at different stages of cycling which allows experimentally verifying the outcome of modeling.