Spherical Si Particles Research Articles

Cyclic deformation behavior of an overaged high-pressure die-cast aluminum alloy

The aim of this study is to identify the deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy in an overaged T7 condition in relation to the significant microstructural changes caused by the overaging heat treatment. The T7 aluminum alloy exhibited a distinctive composite-like microstructure, consisting of coarser α-Al grains and larger spherical Si particles embedded in the matrix, in contrast to its as-cast and T4 counterparts. The softer α-Al matrix of the T7 alloy as revealed by the nanohardness and microhardness led to improved ductility and longer strain-controlled fatigue life at higher strain amplitudes, despite the lower strength. Cyclic stabilization was observed to be a salient feature of the T7 alloy, stemming from the equilibrium between cyclic hardening and cyclic softening. Strain-energy density-based model, by incorporating a material parameter called ‘intrinsic fatigue toughness’, could be used to predict the fatigue life of the alloy.

Nanoscale Al precipitation in the Si phase in AlSi10Mg alloy during electron beam powder bed fusion

Additive manufacturing of Al alloys has garnered attention in the aerospace and automobile industries. This is the first study on the formation of nanoscale Al precipitates in the Si phase of an AlSi10Mg alloy during electron beam powder bed fusion (EB-PBF). Spherical Si particles were homogeneously dispersed in the Al matrix, highlighting the difference from the laser beam PBF (LB-PBF) microstructures. Nanoscale Al phase was formed with a crystallographic orientation relationship with the surrounding Si phase: (111)Si//(111)Al and [11¯0]Si//[11¯0]Al. The formation of Al nanoprecipitates was attributed to an interplay between non-equilibrium solidification, wherein excess Al was dissolved in the Si particles, and the subsequent decomposition of the supersaturated Si phase during high-temperature exposure owing to the preheating procedure. To the best of our knowledge, such formation of Al nanoparticles has not been reported in AlSi10Mg produced through conventional processing or LB-PBF. Thus, the unique thermal history of EB-PBF provides novel opportunities for microstructural evolution, which may be beneficial for the development of novel Al-based alloys.

Development of Spherical Eutectic Si Particles through M-SIMA Process and Its Effects on the Tensile Properties of Al-7Si-0.05Sr Alloy

Development of Spherical Eutectic Si Particles through M-SIMA Process and Its Effects on the Tensile Properties of Al-7Si-0.05Sr Alloy

Effects of solution treatment on microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite fabricated by laser powder bed fusion

This study investigated the effects of solution treatment (ST) on the microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite produced using laser powder bed fusion (LPBF). Microstructural analysis reveals that the grid-like distribution of eutectic precipitates within the as-printed composite disappeared, giving way to the formation of uniformly distributed precipitates. As the ST temperature increased, the content of spherical Si particles decreased, while the content of elongated Al4SiC4 precipitates increased. Matrix grains recrystallization occurred, resulting in a gradual increase in the average grain size from 3.79 μm to 5.23 μm. The preferred crystallographic orientation features along the printing direction, <001> {001} plate texture, were weakened, gradually exhibiting a more disordered growth. The microhardness and tensile strength of the composites exhibited a slight decrease and exhibited a trend of initially increasing and then decreasing with increasing ST temperature. Additionally, the heterogeneity in microhardness along different directions has been reduced. When the ST temperature was 460 °C, the elongation of the composite experienced a significant increase, escalating from 6.12 ± 0.36% to 10.3 ± 0.25%. However, with the increase in ST temperature, it displayed an obvious downward trend. The maximum tensile strength was 449 ± 8 MPa, and the elongation was 9.6 ± 0.4% with the ST temperature of 500 °C. The variations in mechanical properties were primarily attributed to the elimination of grid-like substructure, the uniform distribution of precipitates, and the gradual coarsening of grains. This research was expected to contribute to developing advanced lightweight materials with improved performance, opening up new opportunities for their application in various industries.

Absorption enhancement in visible range from Fano resonant silicon nanoparticle arrays embedded in single crystal Mg:Er:LiNbO3 synthesized by direct ion implantation

Fano resonant Si nanoparticles (NPs) are synthesized in single-crystal Mg:Er:LiNbO3 using ion implantation and subsequent thermal annealing. The structural and optical properties of the Si NPs embedded in the crystal have been investigated. Spherical particles with radius of about 60 nm are observed by cross-sectional transmission electron microscope, while ion beam analysis are used to characterize the NPs formation process. The absorption of the Mg:Er:LiNbO3 crystals have been enhanced significantly due to the embedded Si NPs, which are induced by the Fano resonance effect in the visible light wavelength band. Periodic structures of spherical Si particles model is proposed and analyzed using the Mie theory to study the optical response features and local fields. As a result, numerical simulations demonstrate that periodicities of the array of Si NPs can yield narrow resonant peaks connected with multiple light scattering by the NPs and displaying a Fano-type resonant profile. The wavelengths of the absorption peak show clear red shift with increasing the radius of NPs and the peak intensity can be enhanced by decreasing the array period. This work opens an avenue to modulate the optical filed by embedding Fano resonant Si NPs for potential application in optical devices.

Effect of thermo-mechanical treatment and strontium addition on workability and mechanical properties of Al Si Cu casting alloy

In this study, the potential application of Al-Si-Cu aluminum alloy (ALDC12), which is widely used in the high-pressure die-casting (HPDC) process, for fabricating a wrought product was evaluated. The effects of thermo-mechanical treatment and Sr addition on the microstructure, workability, and mechanical properties of the ALDC12 alloy were investigated in detail. The introduction of thermo-mechanical treatment significantly reduced the interconnectivity of the brittle eutectic Si phase formed during solidification and average grain size. Therefore, the uniformly distributed spherical Si particles and fine grain size considerably improved both the strength and ductility of the ALDC12 alloy. Furthermore, the addition of Sr effectively modified the eutectic Si phase in the casting process, which significantly reduced the occurrence of edge cracks in the subsequent rolling step and further improved the mechanical properties of the final sheets. Consequently, through microstructural control of the ALDC12 aluminum alloy by the thermo-mechanical treatment and Sr addition, it was possible to obtain suitable workability and significantly improved mechanical properties compared with those of cast products.

Meltwater chemistry and characteristics of particulate matter deposited in snow as indicators of anthropogenic influences in an urban area.

A geochemical study of snow from the industrial town of Maribor (Slovenia) was performed. Concentrations of 61 elements in meltwater were determined, and a detailed semi-quantitative and qualitative analysis of individual PTE-bearing particles deposited in snow was performed with SEM/EDS. The physico-chemical characteristics of meltwater reflect the influence of winter road maintenance (high electrical conductivity and high Ca and Na concentrations close to the main roads) and industrial activities. Particulate matter deposited in snow consists mainly of carbonates and silicates, followed by carbon-rich particles and PTE-bearing particles. A higher abundance of PTE-bearing particles is typical for the industrial zones. The size, morphology and chemical composition of 4415 PTE-bearing particles were studied. They were organised into nine groups based on their characteristics. The majority were assigned to the group of Fe-oxides, which includes mostly angular particles of unidentified origin. Several groups of particles of anthropogenic origin were determined, mainly from industrial metal-processing activities. These particles include spherical Fe-oxides, Fe-alloys, other metal alloys and spherical Si-particles. Spherical Fe-oxides are typical for the Tezno industrial zone, while Fe-alloys, namely Fe-Cr (Cu, Mn, Ni) shavings and other metal alloys (Cu-Zn (Cl, Fe) shavings) are typical for the Melje industrial zone. The presence of naturally occurring mineral particles (e.g. zircon, ilmenite, monazite) reflects the influence of natural/geogenic sources on the composition of particulate matter deposited in snow. The presented study confirmed that snow is a very promising medium for the geochemical study of urban environments, especially for the identification of anthropogenic sources of particulate matter.

Correlation between the physical parameters and the electrochemical performance of a silicon anode in lithium-ion batteries

Lithium-ion battery anode used as silicon particles were obtained from different major suppliers, and they were characterized by different spectroscopic techniques and evaluated by electrochemical experiments. Correlations between the key physical parameters and electrochemical properties of the silicon particles were investigated. Silicon particle size, surface oxygen content, -OH content and physical appearance are found to strongly influence the electrochemical properties of the Si anode. The particle size of 100 nm has great promise for the practical application of Si nanoparticles in the lithium-ion battery industry. An inverse correlation between the oxygen content and the reversible capacity or first coulombic efficiency was obtained. The -OH content by surface treatment contributes to enhanced cycling stability by the improved affinity between the Si particle and the water-soluble binder. Spherical Si particles perform better compared to irregular particles, and agglomeration dramatically decreases the cycling stability of the Si anode. Among the investigated Si particles, the sample that exhibited a reversible capacity of more than 2500 mAh g−1, a first coulombic efficiency of 89.26% and an excellent cycling stability, has great potential for use in the battery industry.

Stress-Affected Lithiation Reactions in Elasto-Viscoplastic Si Particles with Hyperelastic Polymer Coatings: A Nonlinear Chemo-Mechanical Finite-Element Study

Stress-affected two-phase lithiation reactions in spherical elasto-viscoplastic Si particles for Li-ion batteries are studied here to determine the effects of a hyperelastic polymer coating on particle stresses, reaction front velocity, and degree of lithiation. The problem is modelled using finite-strain chemo-mechanical equations that couple stress, with Li-ion diffusion and reaction front velocity, and are solved using the finite-element (FE) approach, taking advantage of spherical symmetry of the problem. FE simulations and the sensitivity analysis reveal: (1) coating thickness is the most influential design parameter that affects the velocity of the reaction front, and (2) increasing values of the coating shear and bulk moduli, and the coating thickness reduce tensile circumferential stresses at the edge of the particle. The latter minimises the risk of particle cracking in the opening mode, but it can also accelerate the arrest of the reaction front, and thus reduce the particle lithiation degree in Li-ion battery anodes.

Melting/Solidification of Si Bond Coat Layer in Oxide/Si/RB‐SiC Environmental Barrier Coating System

The effect of melting the Si bond coat layer of a mullite/Si/reaction‐bonded SiC model environmental barrier coating system on the change in its microstructure is studied. Once the Si bond coat layer melts, the molten Si moves toward the RB‐SiC substrate via free Si channels, after which the Si bond coat layer disappears. Just after the onset of solidification of Si, the formation of small spherical Si particles is observed on the surface of the RB‐SiC substrate. This behavior can be attributed to the decrease in the volume of Si owing to a solid–liquid transition and the increase in the volume of Si because of a liquid–solid transition.

Modelling stress-affected chemical reactions in non-linear viscoelastic solids with application to lithiation reaction in spherical Si particles

This paper aims at modelling stress-affected chemical reactions in spherical particles by adopting the chemo-mechanical framework based on the chemical affinity tensor and combining it with the finite-strain non-linear viscoelastic constitutive model. The model is applied to the chemical reaction between lithium (Li) ions and silicon (Si), which has been considered as promising successor to graphite for use as active material in lithium-ion battery (LIB) anodes. However, during charging of LIBs, Si enters into the chemical reaction with Li ions, causing large volumetric expansion of Si particles, which leads to the emergence of mechanical stresses, which, in turn, can affect the kinetics of the chemical reaction even up to the reaction arrest. In this paper, the propagation of the reaction front separating the chemically transformed and the untransformed phases is modelled, and the coupled stress-diffusion-reaction problem is solved using the finite element approach. The model predicts the retardation and the locking of the chemical reaction in Si depending on the values of the chemical energy parameter, which corresponds to experimental observations.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both AI-10%Si-0.3%Mg-Mn and AI-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°Cx3h + 165°Cx6h, AI-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β(Mg5Si6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-AI matrix.

Modeling of Eutectic Formation in Al-Si Alloy Using A Phase-Field Method

AbstractWe have utilized a phase-field model to investigate the evolution of eutectic silicon in Al-Si alloy. The interfacial fluctuations are included into a phase-field model of two-phase solidification, as stochastic noise terms and their dominant role in eutectic silicon formation is discussed. We have observed that silicon spherical particles nucleate on the foundation of primary aluminum phase and their nucleation continues on concentric rings, through the Al matrix. The nucleation of silicon particles is attributed to the inclusion of fluctuations into the phase-field equations. The simulation results have shown needle-like, fish-bone like and flakes of silicon phase by adjusting the noise coefficients to larger values. Moreover, the role of primary Al phase on nucleation of silicon particles in Al-Si alloy is elaborated. We have found that the addition of fluctuations plays the role of modifiers in our simulations and is essential for phase-field modeling of eutectic growth in Al-Si system. The simulated finger-like Al phases and spherical Si particles are very similar to those of experimental eutectic growth in modified Al-Si alloy.

Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of AlSiTi phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Inelastic shape changes of silicon particles and stress evolution at binder/particle interface in a composite electrode during lithiation/delithiation cycling

Inelastic shape changes of Si particles and stress evolution at binder/particle interface was modeled using coupled diffusion–stress framework available in finite element software. A simple model that contains two spherical Si particles with and without the polymer binder film was used to represent the composite electrode. The particles were lithiated and delithiated at two different rates: one representing a slow charging case which results in a uniform Li concentration throughout the Si particles and the other representing a fast charging condition which results in non-uniform lithium concentration within the spherical Si particles. The inelastic shape changes and associated contact forces predicted by the model are qualitatively consistent with experimental data. Further, the effect of binder mechanical properties and the binder fraction on the stress evolution in Si particles and at the binder/particle interface was calculated. The proposed model, although simple, can guide a battery design engineer to choose a proper binder, charge/discharge strategy, and binder fraction for a durable electrode design.

Microstructure and High Temperature Deformation of Extruded Al-12Si-3Cu-Based Alloy

The high temperature deformation behavior of commercial Al-12Si-3Cu-2Ni-1Mg alloy (DM104™) which was fabricated by casting and subsequent hot extrusion was evaluated by compressive tests over the temperature range of 250–470 °C and strain rate range of 0.001–1/s. The extruded alloy had equiaxed grains, spherical Si particles and fine intermetallic phases, such as δ(Al3NiCu) and Q(Al5Cu2Mg3Si6). The true stress-true strain curves from the compressive tests exhibited steady-state flow after reaching the peak stress. A close relationship between the steady-state stress and a constitutive equation for high temperature deformation was observed. Fine equiaxed grains and a dislocation structure within the equiaxed grains were observed in the deformed specimens, suggesting the occurrence of dynamic recrystallization during high temperature deformation.

A selective laser melting and solution heat treatment refined Al–12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

This study shows that a eutectic Al–12Si alloy with controllable ultrafine microstructure and excellent mechanical properties can be achieved by using selective laser melting and subsequent solution heat treatment. This provides a novel and promising approach to the refinement of eutectic Al–Si alloys. Unlike Al–12Si alloys fabricated and refined by traditional methods, the as-fabricated Al–12Si in this study contains nano-sized spherical Si particles surrounding a supersaturated Al matrix. During solution heat treatment, precipitation and coalescence of the Si particles occur, which decreases the Si concentration in the matrix and sub-micron to micron-sized spherical particles embedded in an Al matrix form. The as-fabricated Al–12Si exhibits significantly better tensile properties than the traditionally produced counterparts; while the solution treated Al–12Si has an extremely high ductility of approximately 25%. Importantly, the mechanical properties of the Al–12Si can be tailored through controlling the precipitation and coalescence of the Si particles by varying the solution heat treatment time. A detailed transmission electron microscopy study was conducted to investigate this Al–12Si alloy with ultrafine eutectic microstructure. The excellent tensile properties have been attributed to the refined eutectic microstructure containing spherical Si particles. The formation of this unique microstructure is due to the super heating and an extremely high cooling rate during selective laser melting and the subsequent solution heat treatment, which enables Si to grow along its most stable plane {111}Si.

Gradient microstructure and multiple mechanical properties of AlSi9Cu alloy ribbon produced by melt spinning

The microstructure and mechanical properties of AlSi9Cu alloy ribbons produced by melt spinning were investigated by field emission gun scanning electron microscope (FEGSEM), X-ray diffraction (XRD), tensile and microhardness tests. The solidification time and cooling rate of the 54μm thick ribbon were estimated to be 9×10−5s and 5.72×106Ks−1 respectively. XRD results revealed supersaturated solid-solubility of Si in Al matrix to be 3.03 and 3.57at.% for the wheel side and free surface of the ribbon separately. Microstructure evolution of three gradient regions along the cross-section of the ribbon was studied by SEM in detail, and fine spherical Si particles ranged from 12 to 290nm were found to be distributed both in the Al matrix and the α-Al boundary. The ultimate tensile strength of the ribbon was as high as 383MPa and 1.8times higher than that of the conventional cast ingot, and the breaking elongation of the ribbon was about 1.5% with cleavage fracture feature, while the microhardness of the ribbon was 2.5times higher than that of the ingot.

Microstructure and microhardness of melt-spun Al–25Si–5Fe–XCo (X=0, 1, 3, 5) alloys

The microstructure and microhardness evolution of melt-spun Al–25Si–5Fe alloy with Co addition (1, 3 and 5 wt.%) were investigated. Microstructural and spectroscopic analyses demonstrate that Co could refine primary Si grains and change their morphology because it causes higher constitutional undercooling and has large mixing enthalpy with Si. Especially, 3 wt.% Co addition causes homogeneously distributed fine spherical Si particles in the rapidly solidified Al–25Si–5Fe alloy. The size of the spherical silicon particles was from around 200 to 600 nm near the wheel side region, and it varied from 800 nm to 1.3 μm at the air side. The optimum ratio of Si and Co should be between 6 and 8.3 to form spherical Si grains in Al–25/30Si–5Fe alloys. A considerable improvement in microhardness value (from 211 to 370 HV) was obtained with the addition of Co. ► Microstructure of melt-spun Al–Si–Fe alloy with Co addition was studied. ► Co modifies the primary Si in rapidly solidified Al–Si–Fe alloy. ► Formation of spherical Si particles in Al–Si alloy by Co addition was reported. ► An optimum ratio of Si and Co for formation of spherical Si particles was suggested.

An Al–Si–Ti hierarchical metal–metal composite manufactured by co-spray forming

Spray forming with co-injection of a solid particulate phase to form a homogeneous distribution within the final spray formed billet has been studied as a new route to manufacturing metal–metal composites at large scale with negligible oxide. 12 wt%Ti particles were co-injected into an atomised Al alloy droplet spray and co-deposited to form a ∼300 kg billet at Peak Werkstoff GmbH, Germany. The microstructure comprised refined equiaxed α-Al grains (∼5 μm), spherical Si particles (∼1 μm) and uniformly distributed Ti particles (∼80 μm). Sections of the billet were extruded under a range of conditions into long strips 20 mm wide and 6 mm, 2.5 mm and 1 mm thickness. At high strains, the Ti particles were deformed into continuous fibres of a few microns in thickness. The large interfacial area between the fcc α-Al and hcp Ti inhibited dislocation motion and enhanced tensile properties. Accumulative roll bonding was then performed to higher total strains, while maintaining a constant cross-section, reducing the Ti fibres to sub-micron thickness. The fibres were studied by extraction after selective dissolution of the α-Al matrix. There was no interfacial reaction between α-Al and Ti or any measurable oxide formation.