Size Of Si Particles Research Articles

Effect of Si Content on the Fatigue Fracture Behavior of Wrought Al-xSi-0.7Mg Alloy

The wrought Mg-containing high-silicon aluminum alloy has become more attractive as an ideal structural material, because it has moderate strength and the ductility, high wear and corrosion resistance, low thermal expansion coefficient and low cost. However, as structural material, the fatigue properties and the fatigue fracture behavior of it should be paid much more attention to, especially the effect of Si content on the fatigue properties of wrought Mg-containing Al-Si alloy. In this paper, the wrought Al-(1.44%, 4.92%, 6.61%, 8.81% and 12.4%)Si-0.7%Mg alloy were prepared through DCC and homogenization treatment, and then hot-rolled and cold-rolled into 1.3mm sheets. The microstructure and fatigue fracture morphology of Al-(1.44~12.4)Si-0.7Mg-T4 alloy sheet after fatigue test were investigated by LSCM and SEM. The results showed that the size of Si particles in Al-(1.44~12.4)Si-0.7Mg alloy sheets was approximately the same, but the number of Si particles increased as the Si content increased. The size of recrystallization grain in Al-(1.44~12.4)Si-0.7Mg alloy sheets decreased from 47μm to 10μm when Si content increased from 1.44% to 12.4%, which indicates that increasing of Si content can refine the grain of Al-(1.44~12.4)Si-0.7Mg alloy sheets. With the increasing of Si content the propagation area of fatigue fracture surface of Al-(1.44~12.4)Si-0.7Mg alloy sheets in T4 temper became rougher, and crack propagation became more difficult. Moreover, dimples in the fast fracture area became larger in amount, smaller in size and more uniform in distribution.

Influence of Friction Stir Process on Microstructure and Tensile Properties of LM28 Hypereutectic Al-Si Alloy

This paper reports an investigation of the influence of friction stir processing (FSP) on the microstructure modification, tensile properties and hardness of as cast hypereutectic LM28 Al-Si alloy, aimed to decrease Si particles size, porosity, and enhancing tensile properties. Intense plastic deformation foisted by FSP resulted in a remarkable breaking up of the coarse eutectic and primary silicon particles into smaller ones, and closure of porosity. The area sizes of the fragmented Si particles decreased from 155.1 μm² to around 49.4 μm², aspect ratio of about 2.86 in the as cast condition decreased to around 1.63 after FSP. Porosity was also drastically reduced from 94 µm ECD, in the as cast condition to as low as 7.1 µm ECD. The strength and ductility of the alloy increased simultaneously after FSP. The increase in the tensile strength and ductility values after FSP, as compare to the as cast alloy was around 1.56, and 4.38 times respectively. The LM28 FS-processed alloy displayed an increase in quality index of around 1.97 times higher, than that of the as-cast alloy. The hardness of the alloy increased from 64.6HV for the as-cast alloy to about 85.74HV after FSP. Enhancement in all the properties was largely related to the pronounced changes of the shape, area size and distribution of the silicon particles along with the reduction of porosity FSP.

Porous carbon-coated ball-milled silicon as high-performance anodes for lithium-ion batteries

Si-based anodes are promising candidates for high-performance lithium-ion batteries (LIBs) because they can offer the highest theoretical capacity over conventional graphite-based anodes used in commercial LIBs. However, the large volume change of Si upon cycling results in the degradation of structural integrity and electrode rapid capacity decay. These issues limit the practical applications of Si-based anodes in LIBs. Therefore, porous Si electrodes exhibiting excellent electrochemical performance can be used as anodes in high-energy density LIBs. In this work, we used commercially cheap microsized Si powders to synthesize porous Si via high-energy ball milling and etching processes. The milling time has a significant impact on the morphology, crystallinity, and electrochemical performance of the as-prepared samples. Structural and morphological analyses indicate that the high-energy ball milling greatly reduces the particle size of Si, and on the other hand increases the specific surface area. Porous Si electrodes with pore size of ~ 20 nm were successfully prepared. The 2h-milled porous Si coated with a uniform carbon layer of ~ 4.5 nm exhibits high reversible capacities of 1016.1 and 834.1 mAh g−1 at 1000 and 2000 mA g−1, respectively, over 200 cycles with high coulombic efficiency (> 99.5%), as well as stable cycling. The preparation process is simple, and can be regarded as an alternative route for synthesizing high-performance Si-based anodes for LIBs.

Microstructure and properties of Al-60wt.%Si composites prepared by powder semi-solid squeeze

Al-60wt.%Si composites were successfully prepared by semi-solid squeezing powder mixture of Al and Si at 700 °C. The appearance of about 50wt.% Al-Si metal liquid results that less than 4–5 MPa pressure can squeeze the Al-Si powder mixture to near full density at vacuum condition. The effects of Si particle size on the microstructure and properties of Al-60wt.%Si were investigated. The results show that the composites are consisted of only Si and Al. Si particles distribute evenly in aluminum matrix. Al matrix exhibits a certain preferred orientation under the condition of directional solidification. Si particles with 5 μm size tend to be aggregated into locally interconnected particles and can be effectively passivated. As Si particle size ranges from 10 to 20 μm, the corner passivation effect for Si particles is gradually suppressed. The fracture morphology of Al-60wt.%Si is composed of cleavage platforms of Si grains and fine tearing ridges of Al which tightly wraps Si grains. With the increase of Si particle size from 5 to 20 μm, the flexural strength of Al-60wt.%Si decreases from 270 MPa to 223 MPa, the thermal conductivity increase from 128 to 136 W·m−1·°C−1, and the average coefficient of thermal expansion from ambient temperature to 400 °C ranges from 9.49 to 9.97 × 10−6 °C−1.

Effects of particle size of raw materials on the characteristics of TiB2–SiC composites fabricated from B4C, TiC and Si powders

We studied the effects of particle size of raw materials (B4C, TiC and Si powders) on the characteristics of both TiB2–SiC composite powders and ceramics. Results show that the size of B4C and Si particles hardly affects the size of TiB2 and SiC particles because B4C is decomposed and consumed during the formation of TiB2, and Si is melted during the formation of SiC. The size of SiC particles is within the nano and submicron scale. However, the size of TiC particles determines the sizes of TiB2 particles and TiB2 grains in the composite ceramics because TiC particles serve as templates to form TiB2 particles. Consequently, the microstructure and mechanical properties of the TiB2–SiC composite ceramics are affected. The TiB2–SiC composites fabricated using nano-sized TiC powder possess smaller grain size, better dispersibility and more reasonable crack propagation path, thereby obtaining the optimal mechanical properties (Vickers hardness of 30.2 GPa, flexural strength of 732 MPa and fracture toughness of 7.37 MPa m1/2).

Microstructure and Wear Properties of T6 Heat Treated Semisolid A356-TiB2 composite

The aim of this study is to investigate the microstructure and wear properties of T6 heat treated semisolid A356 composite containing 1.5 wt.% and 2.63 wt.% TiB2. The semisolid A356-TiB2 composite was prepared using a cooling slope casting technique. The sample, then was solution treated at different temperatures (500°C, 520°C and 540°C) for 5 hours soaking time. Then, age hardening was conducted at different temperatures (120°C, 150°C and 180°C) for 8 hours. Semisolid A356 composite was characterized for microstructure, microhardness and wear properties. Microstructure of semisolid A356 composite was refined with a higher amount of TiB2. High solution treated temperature (540°C) resulted in the finer size of Si particles in the semisolid A356 alloy. Microhardness of solution treated semisolid A356 alloy achieved higher hardness at 540°C with a hardness value of 75.16 HV. Solution treated of semisolid A356 composite containing 1.5 wt.% TiB2 has the smallest Si particles and the highest hardness of 119.7 HV. Among the samples, A356-1.5 wt.% composite after aging at 180°C showed the highest hardness (129.7 HV). Wear resistance of semisolid A356 alloys was improved by the addition of TiB2. Wear surface morphology revealed that the adhesive and abrasive wear mechanism present.

In-Operando Observation of Lithium-Silicon Alloy Phase Propagation in Particle-Based Electrodes Using Nanoscale X-Ray Computed Tomography

Silicon (Si) is considered to be one of the most promising anode materials for next-generation lithium-ion batteries primarily due to its high theoretical specific capacity of up to 4200 mAh g-1 and its abundance in nature. However, the irreversible capacity loss and poor cycle life caused by the dramatic volumetric expansion of Si upon alloying with lithium (Li) (>300%) prevents practical implementation of anodes with high Si loading. A better understanding of the interactions between the electrochemistry and mechanical behavior of Si anodes during cycling is therefore needed to develop novel materials and electrode design that can efficiently accommodate the volumetric expansion. In addition, there are significant questions regarding the interactions of the Si with the surrounding carbon materials. In this work, we use nano-resolution x-ray computed tomography (nano-CT) and an in-house micro-capillary sample cell to directly observe the cycling (lithiation/delithiation) process of Si particle-based electrodes as a function of time. We will show preliminary results on the effects of the electrode composition (Si particle size distribution, particle proximity, etc.) on the Li-Si alloy phase nucleation and propagation. This material is based upon work supported by the National Science Foundation under Grant No. CBET-1705321. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Effects of Heat Treatment on the Microstructures and High Temperature Mechanical Properties of Hypereutectic Al–14Si–Cu–Mg Alloy Manufactured by Liquid Phase Sintering Process

Hypereutectic Al–Si alloy is an aluminum alloy containing at least 12.6 wt.% Si. It is necessary to evenly control the primary Si particle size and distribution in hypereutectic Al–Si alloy. In order to achieve this, there have been attempts to manufacture hypereutectic Al–Si alloy through a liquid phase sintering. This study investigated the microstructures and high temperature mechanical properties of hypereutectic Al–14Si–Cu–Mg alloy manufactured by liquid phase sintering process and changes in them after T6 heat treatment. Microstructural observation identified large amounts of small primary Si particles evenly distributed in the matrix, and small amounts of various precipitation phases were found in grain interiors and grain boundaries. After T6 heat treatment, the primary Si particle size and shape did not change significantly, but the size and distribution of CuAl2 (θ) and AlCuMgSi (Q) changed. Hardness tests measured 97.36 HV after sintering and 142.5 HV after heat treatment. Compression tests were performed from room temperature to 300 °C. The results represented that yield strength was greater after heat treatment (RT ~ 300 °C: 351 ~ 93 MPa) than after sintering (RT ~ 300 °C: 210 ~ 89 MPa). Fracture surface analysis identified cracks developing mostly along the interface between the primary Si particles and the matrix with some differences among temperature conditions. In addition, brittle fracture mode was found after T6 heat treatment.

The effect of solution treatment time on the microstructure and ductility of naturally-aged A383 alloy die castings

A383 aluminum alloy high pressure die castings were solution treated at 490 °C for six duration ranging between 15 and 180 min, subsequently quenched in water and naturally aged for 4 days. The effects of solution treatment time on the evolution of microstructure and tensile properties were determined. As expected, Si particles became larger and rounder with increasing solution treatment time. In all cases, the size and aspect ratio of the Si particles followed the lognormal distribution. Moreover, the coarsening of Si particles during solution treatment was found to follow the Lifshitz –Slyozov-Wagner model. A new equation was developed for the evolution of the aspect ratio during solution treatment of Al-Si-Mg alloys. Analysis of tensile properties showed that elongation and quality index increased steadily with increasing Si particle size, a result that is in contrast with the widely accepted notion that large Si particles impairs the ductility of cast Al-Si-Mg alloys. The positive correlation between Si particle size and quality index was interpreted to be due to partial healing of oxide bifilms entrained in the castings.

Effects of Zr Additive on Microstructure, Mechanical Properties, and Fractography of Al-Si Alloy

The effects of Zr additive on the microstructure, mechanical properties, and fracture behavior of Al-Si alloy were systematically investigated. The additive of Zr obviously reduced the size of Si particles and changed its morphology. Grain size refinement was promoted by the reaction between Al and Zr forming Al3Zr and ZrSi2 compounds. Compared to a Zr-free alloy, the additive enhanced the tensile strength, compressive strength, shear strength, and hardness. The optimized Zr content was 2.4 wt % corresponding to a tensile strength of 231.1 MPa, compressive strength of 343.1 MPa, shear strength of 174.9 MPa, and hardness of 85.5 HV, greater than those of the Zr-free alloy. This illustrates that fine-grain strengthening and the existence of a second phase can improve the mechanical properties of Al-Si alloy. The fracture surface of Al-Si alloy without Zr additive showed a brittle fracture mode and there were no pits on the fractured surface. In the presence of Zr addictive, a typical plastic deformation with a large amount of pits was evidenced.

Synthesis of Co-doped β-FeSi2/Si composites through eutectoid decomposition and its thermoelectric properties

We attempted to synthesize composites of Co-doped β-FeSi2 thermoelectric material with fine Si dispersion from α phase composition of Fe2Si5. We annealed the sintered bodies through eutectoid decomposition of high-temperature α phase to low-temperature semiconducting β phase in Fe–Si system. As a result, we obtained micro to nanoscale differences in Si distribution caused by the different annealing times and temperatures. Sizes of dispersed Si particles ranged between 100 and 300 nm. Seebeck coefficient of Co-doped β-FeSi2 with Si dispersion is higher than that of the conventional singular phase Co-doped β-FeSi2. This value overpowers the increase in electrical resistivity and thermal conductivity, thus elevating the dimensionless figure of merit, ZT from approximately 0.05–0.085. Furthermore, thermal conductivity of Co-doped β-FeSi2/Si composite annealed at 800 °C for 4 h was lower than calculated value from the rule of mixture where dispersed structure was not considered in the calculation. This proves that Si dispersions help suppress thermal conductivity.

One-Step Electrodeposition of Layer by Layer Architectural Si-Graphene Nanocomposite Anode of Lithium Ion Battery with Enhanced Cycle Performance

One step electrodeposition is applied to prepare Si-Graphene (SiG) composites from Graphene(G)-SiCl4 -[BMP]tf2N ionic liquid. The SiG composites have shown an alternate layer-structure of Si and graphene caused by alternate processes of Si reduction and graphene adsorption on the electrode, which is confirmed by the regular current pulsation in the chronoamperometric curves during the whole electrodeposition process. The SEM and TEM morphologies indicate that each layer is about 120 nm thickness for the SiG3 composites electrodeposited from the 0.1852 mol · l− 1 Graphene(G)-SiCl4 -[BMP]tf2N ionic liquid, in which Si particle size is about 80–110 nm closely stick on 4–5 layers of graphene with a molar ratio of Si and C of 4.57:1. SiG3 anode displays a specific capacity of 1378 mAh · g−1 at the initial cycle, and 1083 mAh · g−1 at the end of 400 cycle (retention of 78%) at 4 A · g−1, as well as 988 mAh · g−1 at 8A · g−1, showing a good cycle life and rate performance. The layer-structured SiG anode significantly improve the conductivity and electrochemical performances of Si anode. The research provides a feasibility for electrodeposition preparation of layer-structured materials, especially for semiconductor-based alloys, graphene-based alloys in large-scale.

Particle size effect on the thermal conductivity reduction of silicon based thermoelectric composites

Thermal conductivity reduction in environmentally friendly thermoelectric composites with varying Si particle size has been experimentally measured and modelled using the crowding-factor model.

Effect of load on the tribological properties of hypereutectic Al–Si alloy under boundary lubrication conditions

Researchers reported that the IC engine components (piston, cylinder liner etc) fail due to the friction losses (~45%) and wear losses (~25–40%). So the demand of light weight, low friction and wear resistance alloys increases day by day, which reduces the emission and increases the efficiency of the IC engine. In this connection, tribological tests on hypereutectic Al–25Si alloy were performed using a ball-on-disk configuration under dry and lubricated sliding conditions. Hypereutectic Al–25Si alloy was prepared by rapid solidification process with T6 condition. T6 condition improves the friction, wear and mechanical properties of the alloy. Friction coefficient and wear rate of the alloy was measured under high loads ranging from 100 to 300 N. It was found that the friction coefficient (COF) and wear rate of hypereutectic Al–25Si alloy/steel tribo pair increased with increase in load. Significant reduction in COF and wear rate was accomplished with SAE20W50 engine oil and Si particles act as solid lubricant. Optical microscope, 3D surface profilometer and scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) were used for characterization the worn surface morphologies. The morphology, size and distribution of high Si particles due to its fabrication process caused the improvements in COF and wear rate under lubricated conditions. Adhesive wear, abrasive wear and plastic deformation acted as the dominant wear mechanism for hypereutectic Al–25Si alloy.

Spheroidization of Si in Al–12.6wt.%Si at eutectic temperature and its tensile properties

The morphology of Si affects significantly the mechanical properties of eutectic Al–Si alloy. In this letter, we report a novel method for the spheroidization of Si in eutectic Al–Si alloy. The results show that Si in eutectic Al–Si alloy could be spheroidized after annealing at eutectic temperature for 3 h. Si phase in the alloy exists in the form of ellipsoidal particles without faceted edges. The surface shape factor of Si phase is 0.8 and the average size of Si particles is only 3.3 µm. Compared with cast eutectic Al–Si alloy, the tensile strength and the hardness of the annealed alloy are decreased by 8.2% and 8.6%, respectively, but its elongation is increased by 79.4%. The fracture mode of Al–12.6%Si alloy annealed at 577 °C for 3 h belongs to ductile fracture.

Facile Thermal and Optical Ignition of Silicon Nanoparticles and Micron Particles.

Silicon (Si) particles are widely utilized as high-capacity electrodes for Li-ion batteries, elements for thermoelectric devices, agents for bioimaging and therapy, and many other applications. However, Si particles can ignite and burn in air at elevated temperatures or under intense illumination. This poses potential safety hazards when handling, storing, and utilizing these particles for those applications. In order to avoid the problem of accidental ignition, it is critical to quantify the ignition properties of Si particles such as their sizes and porosities. To do so, we first used differential scanning calorimetry to experimentally determine the reaction onset temperature of Si particles under slow heating rates (∼0.33 K/s). We found that the reaction onset temperature of Si particles increased with the particle diameter from 805 °C at 20-30 nm to 935 °C at 1-5 μm. Then, we used a xenon (Xe) flash lamp to ignite Si particles under fast heating rates (∼103 to 106 K/s) and measured the minimum ignition radiant fluence (i.e., the radiant energy per unit surface area of Si particle beds required for ignition). We found that the measured minimum ignition radiant fluence decreased with decreasing Si particle size and was most sensitive to the porosity of the Si particle bed. These trends for the Xe flash ignition experiments were also confirmed by our one-dimensional unsteady simulation to model the heat transfer process. The quantitative information on Si particle ignition included in this Letter will guide the safe handling, storage, and utilization of Si particles for diverse applications and prevent unwanted fire hazards.

Wear Performance of A356 Matrix Composites Reinforced with Different Types of Reinforcing Particles

To improve the wear resistance of Al-Si alloys, different types of reinforcing particles such as SiC, TiC, ZrO2, and B4C were used to produce matrix composites by friction stir processing (FSP). First, microstructural properties of different locations of stir zone (SZ) in the FSPed specimens such as advancing side, retreating side, shoulder-affected area, and pin-affected area were investigated. The results demonstrate that Si particles size is not the same in different SZ subdomains. SEM investigation was performed in order to investigate the particles distribution in different areas of the SZ as well as bonding quality between particles and metal matrix. Hardness and wear tests were carried out to determine mechanical and wear properties of the composites. The pin-on-disk wear tests were performed at room temperature, with the normal applied loads of 5, 10, and 20 N and sliding speed of 1 and 2 m/s. All fabricated composites show higher resistance in wear than A356 alloy. Wear test results show, by increasing the normal load and sliding velocity, the wear loss weight of all composites increased gradually.

Cycling Behavior of Silicon-Containing Graphite Electrodes, Part A: Effect of the Lithiation Protocol

Silicon (Si) is a promising additive for enhancing the specific charge of graphite negative electrodes in Li-ion batteries. However, Si alloying with lithium leads to an extreme volume expansion and in turn to rapid performance decline. Here we present how controlling the lithiation depth affects the performance of graphite/Si electrodes when different lithiation cutoff potentials are applied. The relationship between Si particle size and cutoff potential was investigated to clarify the interdependence of these two parameters and their impact on the performance of Si-containing graphite electrodes. For Si with a particle size of 30–50 nm, Li15Si4 is only formed for the potential cutoff of 5 mV vs Li+/Li, whereas using a higher cutoff of 50 mV has no impact on the performance. For larger Si nanoparticles, 70–130 nm in size, Li15Si4 is already formed at 50 mV. However, in these larger particles only 70% of the Si initially participates in the lithiation, independent of the cutoff potential (5 or 50 mV), and the performance fades rapidly. For the highest tested cutoff potential of 120 mV, the contribution of larger Si particles to the specific charge of the electrodes was negligible, but for the smaller particles a stable and still significant Si specific charge was obtained.

Tribological Characterization of Hypereutectic Al–25Si Alloy Under Dry and Lubricated Sliding Conditions

Friction and wear properties of hypereutectic Al–25Si alloy were studied under dry and lubricated sliding conditions. Hypereutectic Al–25Si alloys were prepared by rapid solidification process (RSP) under the T6 condition. Experimental studies were conducted using a ball on disk type tribometer. The effect of the sliding distance and normal load on the friction and wear were investigated. The coefficient of friction (COF) remained stable with an increase in the sliding distance (250–1500 m) and decreased with an increase in the normal load (10–50 N), whereas the wear rate decreased with an increase in the sliding distance, and increased with the increase in the normal load up to 40 N and then attained a steady-state value under dry and lubricated sliding conditions. The improvements in COF and wear rate were mainly attributed to the morphology, size, and distribution of hypereutectic Si particles due to its fabrication process. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), optical microscopy, and three-dimensional (3D)-surface profilometer were used for characterization of the wear tracks. The dominant wear mechanisms for a hypereutectic Al–25Si alloy were adhesive wear, abrasive wear, and plastic deformation.

Effects of Process Parameters on Solidification Structure of A390 Aluminum Alloy Hollow Billet

The effects of process parameters on the solidification structure of A390 aluminum alloy hollow billets prepared by direct-chill casting were investigated. The decrease of casting temperature deteriorated the homogeneity and increased the size of primary Si particles in the hollow billet. Although the average size of primary Si particles was not obviously affected by the increase of casting speed, the thickness of Si-depleted layer at the inner wall increased with the higher casting speed. The tensile strength of A390 alloy is a function of the percentage of coarse Si particles (larger than 35 μm) and the average size of primary Si particles. Higher and more stable tensile strength can be received in the hollow billet with the casting temperature of 1050 K (777 °C), because the fine and uniformly distributed primary Si particles were obtained in the hollow billet.