Microstructure Of Silicon Research Articles

Effects of casting conditions on AlSi21CuNi hypereutectic alloy structure modified with P/Sr microadditions

The study aims to evaluate the influence of selected modification parameters with phosphorus and strontium on the structure of the AlSi21CuNi alloy.Test smelting was conducted using a metal bath heating temperature of 850C for 30 minutes. Once the temperature of the liquid metal was reduced to 750C, the modification procedure was carried out. Casting was carried out using a metal mould at 10, 30 and 60 minutes after the modifiers were introduced into the metal bath. The first smelting involved the application of an AlCuP modifier at 350 ppm P by weight of the alloy. The next three smeltings were carried out by simultaneously introducing AlCuP (180 ppm P) and AlSr modifier (150, 250, 350 ppm Sr) into the metal bath. The last smelting was carried out to obtain samples of unmodified silumin. The smelting was carried out using the same procedure as for the modified alloy, omitting the introduction of modifiers into the metal bath.The conducted modification treatments were evaluated using qualitative and quantitative analysis methods of the microstructure of samples taken from test castings. The metallographic studies were carried out using a scanning electron microscope (SEM) and computer image analysis software.It has been found that the simultaneous modification, i.e. with phosphorus and strontium additives of primary silicon crystals and refinement of the eutectic, represents a compromise between satisfactory fragmentation of the primary silicon crystals and the degree of refinement of the eutectic. The contact time of the modifiers with the metal bath is an important modification parameter in the given context. Further studies on the complex modification with phosphorus and strontium of other alloys from the group of hypereutectic silumins are justified in order to obtain material properties satisfactory to customers, i.e. manufacturers of various types of products.The simultaneous modification of primary and eutectic silicon into hypereutectic silumins is the key to improving their mechanical properties and wear resistance, which translates into the possibility of producing lightweight components for the automotive industry.The paper presents the results of metallographic studies of the AlSi21CuNi alloy before and after modification treatments in the form of qualitative and quantitative analyses of the microstructure of primary and eutectic silicon.

Effect of Mg alloying and cooling rate on the microstructure of silicon

Effect of Mg alloying and cooling rate on the microstructure of silicon

Effect of Local Pressurization on Microstructure and Mechanical Properties of Aluminum Alloy Flywheel Housing with Complex Shape.

In this work, squeeze casting experiments of flywheel housing components with a large wall thickness difference and a complex shape were carried out with AlSi9Mg aluminum alloy. The defects, microstructures, and mechanical properties under different process parameters were investigated. Furthermore, the local pressurization process was applied to the thick-walled positions to force-feed the cast defects. The mechanical properties and microstructures at these positions were analyzed. The results showed that the surface quality of formed components was good and that local pressurization could effectively reduce the shrinkage cavity and shrinkage porosity in thick walls, but the scope and effect of forced feeding were limited. The optimum process parameters were a pouring temperature of 650 °C, a specific pressure of 48 MPa, a mold temperature of 220 °C, a local pressurization of 800 MPa, and pressure delay times of 15 s (side A) and 17 s (side B). The ultimate tensile strength, yield strength, and elongation of the formed component under validation experiments of the optimum process parameters were 201 MPa, 103 MPa, and 5.1%. Meanwhile, the fine grains of primary α-Al were mainly rosette and equiaxed grains, and the average grain size was about 40 μm. The microstructure of the eutectic silicon was acicular and was prone to segregation under pressure. According to profile morphology, the positions after pressurization were divided into a deformation zone, a direct action zone, and an indirect action zone. The coexistence of as-cast and plastic deformation microstructures was observed. The effect of local pressurization mainly involved a change in the solidification process, plastic deformation, and forced feeding.

3D surface microstructure of silicon modified by QDs to improve solar cell performance through down-conversion and anti-reflection mechanism

Improving the photoelectric conversion efficiency (PCE) of solar cells is an important subject for a wide range of photovoltaic research. One of the main reasons for low PCE is the mismatch between solar spectrum and solar cells. The use of down-conversion and anti-reflection mechanisms is a reasonable method to increase PCE. Down-conversion can convert low-absorbance photons in silicon solar cells into high-absorbance photons while the special 3D surface structure formed by the down-conversion material produces an anti-reflection effect to increase the PCE of the solar cell. In this study, cadmium selenide (CdSe) quantum dots (QDs) coating hybrid structure of monocrystalline silicon solar cells was proposed to increase the utilization. Here, the CdSe QDs were synthesized with a high absorption strength in the 300–500 nm and a photoluminescence (PL) peak at 628 nm. Benefiting from the larger absorption cross-section and weaker electron-phonon coupling characteristics of CdSe QDs, the down-conversion was achieved successfully, and the reflectance test of the CdSe QDs covered silicon solar cells also shows an anti-reflection effect. Therefore, by using the dual mechanism of down-conversion and anti-reflection, the PCE of solar cells was improved by the proposed system. The results show that the PCE of the CdSe QDs coating hybrid structure based monocrystalline silicon solar cells is increased by 1.42% from 14.45% to 15.87%. Besides, by using finite element method, the reflection reduction mechanism for lower transition layer was also simulated to further explain the experiment results. Due to the low synthesis cost of QDs, this work can be well integrated into the photovoltaic industry, which provides a new technical route and guidance for improving the PCE of silicon cells.

Aging characteristics and lifespan prediction for composite insulator silicone rubber in a mountainous region environment

In this study, the aging process of composite insulator silicone rubber in a mountainous region environment was studied and a lifespan prediction model was constructed. Silicone rubber samples with various exposure times were analyzed based on the microstructure, physical properties, functional groups, and chemical environment of silicon. All experimental results corresponded to three aging stages: platform stage, upturn stage, and acceleration stage. Based on linear regression method, the peak content of Si(-O)2 and shore hardness A were selected to establish the lifespan prediction model for silicone rubber. Verification of the model showed that the residual lifespan error is less than 1.5 years. This study is based on a systematic analysis of three stages of the aging process for silicone rubber in composite insulators and obtaining critical aging parameters. Furthermore, a lifespan prediction model is proposed and validated.

Microstructural Characteristics, Modeling of Mechanical Strength and Thermal Performance of Industrial Waste Glass Blended Concrete

The need to get rid of solid waste in the environment necessitates the incorporation of waste glass powder (WGP) in mortar and concrete. The blending of WGP (G) with ordinary Portland cement (OPC) is a valorization technique that is not only cost efficient but also environmentally friendly. The replacement level is denoted as CxG10−x, where x is 0–20 wt.% at an interval of 5 wt.% in mortar (w/b = 0.4) and 0, 10, 20 and 30 in concrete (w/b = 0.42). The study investigates the effects of glass on the setting, workability, thermal resistance, microstructure, mineral phases and bond characteristics of silicon and hydroxyl-based compounds and C-O vibrations. It also provides the model equations for strength characteristics in terms of OPC, G and ages in mortar and concrete on one hand and investigates the residual strength and density of glass blended concrete at elevated temperature (550 °C) on the other. It is found that glass enhances the workability, reduces the setting time and density and enhances the residual strength and density of concrete. The presence of glass leads to the formation of coesite and microstructural distortion and decreases the Ca/Si ratio. Besides, the bond characteristics of the binder are significantly affected, while the thermal residual strength capacity in glass blended concrete (C80G20) is 40.4% and 75.14% lower than that in OPC concrete (C100G0) because of the low thermal conduction of glass particles. The optimum glass content in mortar and concrete to produce 33 MPa (28 days) and 47 MPa (90 days) is found to be 10 wt.% and 20 wt.%, respectively.

The effect of Si addition on the heterogeneous grain structure and mechanical properties of CrCoNi medium entropy alloy

In this study, CoCrNi MEAs added with different silicon contents (0, 0.1, 0.2 for molar ratio) were prepared by arc melting. The cold rolled and annealed microstructural evolution and tensile mechanical behavior of the alloys were systematically investigated. The results show that the distribution of elements in the alloys after homogenization annealing is uniform. As the rolling reduction increased from 20% to 60%, SEM-BSE characterization showed that the deformed microstructure of the alloys transformed from neatly aligned slip bands to tangled shear bands. TEM characterizations show that the alloys have typical cold rolling-induced microbands, dislocation cells, and high-density dislocation walls caused by plane slip after cold rolling for 60%. Also, these deformed microstructures are finer in size concerning silicon-alloyed MEAs compared to silicon-free MEAs. After annealing at 650 °C for 60 min, the deformed microstructure was replaced by a heterogeneous grain structure composed of ultrafine grains, micron-scale grains, high-density dislocation regions, and residual deformation regions. With the increase of Si content, the yield strength and tensile strength increased with the change of the heterogeneous grain structure. The tensile strength of the Si0.2 MEAs even exceeds 1.5 GPa, and still maintains a uniform elongation greater than 20% at 77 K. The evolution of the cold-rolled microstructure of silicon alloyed MEAs are mainly related to the reduction of stacking fault energy and a strong dependence on grain orientation and applied stress direction. The formation of nano-DTs and HCP phases resulted in the excellent combination of strength and ductility at 77 K. The typical heterogeneous grain structure realizes the strength–ductility synergy of the alloys.

Research on Microstructure and Growth Mechanism of Different Primary Silicon in Hypereutectic Aluminum Alloy

The as-cast microstructure of a typical hypereutectic Al-25Si alloy was studied, and the growth mechanism of different primary silicon phases was analyzed. The results show that the as-cast microstructure phase composition of the alloy is mainly primary silicon and eutectic silicon. Primary silicon is mainly petal-like, massive and other complex polyhedrons, and there are a lot of cavities, cracks and other defects in the interior and boundary; Eutectic silicon is coarse and long needle-like, and the distribution is relatively messy, which seriously deteriorates the mechanical properties and cutting performance, and hinders the further application of the alloy in the field of lightweight pistons. Petal-shaped primary silicon is grown by combining five tetrahedral crystal nuclei in the melt into a decahedron, while bulk primary silicon is mainly caused by the unbalanced aggregation of impurity elements. And these two types of silicon phase growth methods are related to the twin groove growth mechanism, which is the result of a combination of multiple mechanisms.

Microstructure and Oxidation Behavior of Metal-Modified Mo-Si-B Alloys: A Review

With the rapid development of the nuclear industry and the aerospace field, it is urgent to develop structural materials that can work in ultra-high temperature environments to replace nickel-based alloys. Mo-Si-B alloys are considered to have the most potential for new ultra-high temperature structural material and are favored by researchers. However, the medium-low temperature oxidizability of Mo-Si-B alloys limits their further application. Therefore, this study carried out extensive research and pointed out that alloying is an effective way to solve this problem. This work provided a comprehensive review for the microstructure and oxidation resistance of low silicon and high silicon Mo-Si-B alloys. Moreover, the influence of metallic elements on the microstructure, phase compositions, oxidation kinetics and behavior of Mo-Si-B alloys were also studied systematically. Finally, the modification mechanism of metallic elements was summarized in order to obtain Mo-Si-B alloys with superior oxidation performance.

Insights into the local structure, microstructure and ionic conductivity of silicon doped NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12

NASICON-type solid electrolyte Li1.3Al0.3Ti1.7P3O12 (LATP) is attractive because of the cheap raw materials, excellent air stability, and high ionic conductivity. Silicon doping is generally adopted to improve its conductivity further, but the corresponding mechanism is vacant. Herein, we synthesize the silicon doped LATP electrolyte with a simple solution-based method and systemically investigate the effects of different silicon doping level on the local structure, microstructure and ionic diffusion kinetics of the solid electrolytes. We firstly put forward the octahedral occupation of silicon in Li1.3Al0.3Ti1.7P3O12 electrolyte instead of tetrahedral sites. Silicon doping is found to be negative for the ionic transportation in grain bulk, however, the grain boundary conductivity can be increased after a small amount of silicon doping due to the modification of micro-structure, i, e., the silicon doping induces the segregation of LiTiOPO4 in the grain boundary, which can effectively suppress the abnormal growth of electrolyte grains and concomitant gas pores and cracks during sintering. As a result, the total conductivity can reach ∼10−3 S⋅cm−1 after silicon doping with this simple method. Our results demonstrate the critical importance of adjusting secondary phase on the micro-structure and ionic conductivity of electrolyte during the development of inorganic fast ionic conductors.

Influence of Artificial Aging in Aluminum Silicon Alloy

One of the techniques to increase the hardness of aluminum alloy is by aging process. The aging process includes natural aging and artificial aging processes. This study aims to investigate the effect of artificial aging on the hardness of aluminum silicon alloys. Artificial aging is carried out at two temperature variations, namely 150 and 200 °C. Metallographic test using optical microscopy and scanning electron microscopy were performed to observe the microstructure and deposits of silicon. Investigation of the constituent elements of aluminum silicon was carried out using the Energy Dispersive X-Ray Spectroscopy technique. The mechanical properties of aluminum silicon alloys examined were hardness before aging and hardness after artificial aging at temperatures of 150 and 200 °C. Hardness testing is conducted by Rockwell B hardness testing. The hardness test results showed that the hardness before the aging process was 61.1 HRB, the hardness after artificial aging at 150 °C was 69.11 HRB and the hardness after artificial aging at 200 °C was 80.36 HRB. There was an increase in hardness after the artificial aging process was carried out.

Formation mechanism and conditions of fine primary silicon being uniformly distributed on single αAl matrix in Al-Si alloys

In this study, solidification microstructure of fine primary silicon being uniformly distributed on single αAl matrix was obtained when adding Cu–9 wt%P alloy to an Al–10 wt%Si alloy melt or an Al–20 wt%Si alloy melt, stirring at 200 r/min for 12 min and cooling at the cooling rate of 16.3 K·s−1. The change law of silicon phase size with cooling rate and modified treatment parameters was determined by examining the solidification microstructures. It was found that ultrafine AlP was easily swallowed by primary silicon when the cooling rate was slow. The formation mechanism of superfine AlP particles, the growth process of αAl phase around primary silicon and the disappearance process of eutectic silicon were researched under intense stirring of the melt during the Cu–9 wt%P alloy modification. Moreover, the conditions under which fine primary silicon was uniformly distributed in single αAl matrix in hypereutectic Al-Si alloy were put forwarded. Finally, the formation mechanism of the solidification microstructure without eutectic Si in hypereutectic Al-Si alloy was analyzed.

Silicon Nanotubes as Potential Therapeutic Platforms.

Silicon nanotubes (SiNTs) with unique well-defined structural morphologies have been successfully fabricated and recognized as a novel architecture in the nanoscale Si family. While the typical dendritic microstructure of mesoporous silicon prepared anodically has been exploited previously for therapeutics and biosensing, our status of utilizing SiNTs in this regard is still in its infancy. In this review, we focus on the fundamental properties of such nanotubes relevant to therapeutic applications, beginning with a description of our ability to sensitively tune the structure of a given SiNT through synthetic control and the associated detailed in vitro dissolution behavior (reflecting biodegradability). Emphasis is also placed here on the range of functional moieties available to attach to the surface of SiNTs through a summary of current studies involving surface functionalization and strategies that facilitate conjugation with molecules of interest for multiple purposes, including cell labeling, nucleotide attachment, and scaffolding of therapeutic metallic nanoparticles. Experiments addressing our ability to load the interior of a given nanotube with species capable of providing magnetic field-assisted drug delivery are also briefly described. Given the range of diverse properties demonstrated to date, we believe the future to be quite promising for employing SiNTs as therapeutic platforms.

Effect of low-temperature annealing on void-related microstructure in amorphous silicon: A computational study

We present a computational study of void-induced microstructure in amorphous silicon (a-Si) by generating ultra-large models of a-Si with a void-volume fraction of 0.3%, as observed in small-angle X-ray scattering (SAXS) experiments. The relationship between the morphology of voids and the intensity of scattering in SAXS has been studied by computing the latter from the Fourier transform of the reduced pair-correlation function and the atomic-form factor of amorphous silicon. The effect of low-temperature annealing on scattering intensities and the microstructure of voids has been addressed, with particular emphasis on the shape and size of voids, by studying atomic rearrangements on void surfaces and computing the average radius of gyration of the voids from the spatial distribution of surface atoms and the intensity plots in the Guinier approximation. The study suggests that low-temperature annealing can lead to considerable restructuring of void surfaces, which is clearly visible from the three-dimensional shape of the voids but it may not necessarily reflect in one-dimensional scattering-intensity plots.

Effect of quenching and partitioning on the microstructure and mechanical properties of a medium carbon low alloy low silicon (0.3C–1.0Mn–0.4Si–0.6Cr–0.46Ni–0.26Mo) steel

The importance of advanced high strength steel having high strength with balanced ductility has led to immense researches all over the world for increasing the strength to weight ratio in different structural applications. The results of quenching and partitioning (QP) heat treatment process on a hot rolled advanced medium carbon steel (0.3C–1.0Mn–0.4Si–0.6Cr–0.46Ni–0.26Mo) have been analyzed in the present investigation. Hardness, tensile and yield strength of the steel show considerable improvement after the heat treatment process. Microstructural analyses by Optical, Scanning and Transmission Electron Microscopes show the creation of smaller units and sub-units of multiple phases containing martensite, retained austenite and bainite in the QP steel than those of as-received steel. Microstructure evolution was assessed by conducting the heat treatment with different isothermal partitioning times followed by x-ray Diffraction phase analyses. Austenite content has been found to increase with the duration of partition. Mechanical properties were related with the microstructures obtained at different stages of partitioning. Formation of thin retained austenite films in the periphery of individual bainite and martensite strips, blocks of austenite and the presence of overall small microstructural features have been proposed to be the reason for the improvement in hardness, tensile and yield strength and ductility of the as received hot rolled steel after the designed quench and partitioning treatment.

Comparative Study of Furnace and Flash Lamp Annealed Silicon Thin Films Grown by Plasma Enhanced Chemical Vapor Deposition

Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below the softening point of glass substrate. The initial a-Si films were grown by plasma enhanced chemical vapor deposition (PECVD). Reflectance measurement indicated characteristic peak in the UV region ~280 nm for the furnace annealed (>550 °C) and flash lamp annealed films, which provided evidence of crystallization. The film surface roughness increased with increasing the annealing temperature as well as after the flash lamp annealing. X-ray diffraction (XRD) measurement indicated that the as-deposited samples were purely amorphous and after furnace crystallization, the crystallites tended to align in one single direction (202) with uniform size that increased with the annealing temperature. On the other hand, the flash lamp crystalized films had randomly oriented crystallites with different sizes. Raman spectroscopy showed the crystalline volume fraction of 23.5%, 47.3%, and 61.3% for the samples annealed at 550 °C, 650 °C, and with flash lamp, respectively. The flash lamp annealed film was better crystallized with rougher surface compared to furnace annealed ones.

A fractal-like texture of multicrystalline silicon for enhancing optical performance

Appropriate texturing is one major topic for multicrystalline silicon wafers to improve the cost effectiveness. In this paper, a new fractal-like texture being applied to multicrystalline wafers is introduced. The focus of this paper is the study of the light-trapping ability of the novel fractal-like texture for multicrystalline silicon solar cell. With a simple model of the fractal-like texture, the conditions needed to achieve lower reflectance are discussed first. It is shown how the effect of the micro structure of multicrystalline silicon with the fractal-like characteristics. Finally, in our present work, the finite element method(FEM) is used to simulate the propagation of electromagnetic field in the structure of multicrystalline silicon. We obtain an average reflectivity of 3% in the wavelength range 300–800 nm on the surface of multicrystalline silicon wafer, which has the fractal-like structure feature.

Effect of substrate bias voltage on tensile properties of single crystal silicon microstructure fully coated with plasma CVD diamond-like carbon film

Tensile strength and strength distribution in a microstructure of single crystal silicon (SCS) were improved significantly by coating the surface with a diamond-like carbon (DLC) film. To explore the influence of coating parameters and the mechanism of film fracture, SCS microstructure surfaces (120 × 4 × 5 μm3) were fully coated by plasma enhanced chemical vapor deposition (PECVD) of a DLC at five different bias voltages. After the depositions, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal desorption spectrometry (TDS), surface profilometry, atomic force microscope (AFM) measurement, and nanoindentation methods were used to study the chemical and mechanical properties of the deposited DLC films. Tensile test indicated that the average strength of coated samples was 13.2–29.6% higher than that of the SCS sample, and samples fabricated with a −400 V bias voltage were strongest. The fracture toughness of the DLC film was the dominant factor in the observed tensile strength. Deviations in strength were reduced with increasingly negative bias voltage. The effect of residual stress on the tensile properties is discussed in detail.

Influence of direct electric current on solidification process of Al–Si alloy

The effect of direct electric current on redistribution and microstructure of primary silicon in Al–Si melt during the solidification refining process was studied. Electric current generates a Joule heat, which slows down the cooling rate of the furnace. The precipitated area of primary silicon decreases from 100% to 36.67% with the increase of current density from 0A/m2 to 1.5×106 A/m2. Furthermore, direct current causes a convection leading to the migration of primary silicon in the opposite direction of electric field, which forms the accumulation area. The morphologies of primary silicon and the redistribution of B impurity were investigated under the effect of electric current.

Microstructure and Creep Properties of Silicon- and/or Germanium-Bearing Near-α Titanium Alloys

The effects of Si and/or Ge addition on the microstructure and creep properties at 650°C and 137 MPa were investigated in near-α Ti–Al–Sn–Zr–Mo alloys. Si and/or Ge addition decreased the minimum creep strain rate owing to the solid solution of Si and Ge in the matrix and the precipitation of silicide, germanide, and their solid solutions. The decrease in the minimum creep strain rate in the alloy with 1 wt% Ge without Si was the most significant because of the formation of very fine germanide precipitates. In addition, a marked shift in the lattice parameters of the α and β phases was detected for the alloy with 4 wt% Ge. The Moiré fringe patterns at the α/β interfaces in the alloys were investigated using high-resolution transmission electron micrographs to discuss the alloying effect on the structure of the interfaces.