Addition Of Silicon Research Articles

Self-assembly of hierarchical ZSM-5 particles on rice husk template as hybrid catalysts for boosting methanol aromatization

Herein, natural rice husks with hierarchically porous structures were used as a platform to assemble ZSM-5 particles (denoted as hierarchical ZSM-5) to improve diffusion properties in the methanol-to-aromatics (MTA) reactions. Rice husk could work as the platform to immobilize zeolite grains and provide additional silicon sources for the growth of zeolite particles. Sodium hydroxide amount and SiO2/Al2O3 ratio strongly determined the acid properties, and the rotational crystallization condition favored the zeolite formation. Improved diffusion properties of hierarchical ZSM-5 particles were confirmed by comprehensive pore analysis and benzene diffusion experiments, showing an excellent diffusion property towards aromatic molecules. Compared with commercial microporous zeolite in the catalytic MTA reaction, hierarchical ZSM-5 exhibited superior aromatics selectivity (40.8 vs. 35.8 %), higher liquid hydrocarbon yield (22.3 vs. 14.7 wt%), and longer lifetime (60 vs. 40 h). These results offer new insights into the controllable synthesis of Hier-ZSM-5 with a hierarchically porous structure using biomass as templates.

Effect of Rolling at Moderate Temperature on Mechanical and Physical Behavior of the Light Weighted Composite Materials

Abstract: An application of the light weight martials play the significant role in the modern industries. Such materials along with the high strength to weight ratio and significant mechanical attributes utilized to fabricate the new generation materials for automobile industries. Al and its alloy have been utilized widely in the current automotive industries, especially addition of silicon in aluminium alloy provide significant improvement in Mechanical and physical properties. In the current study Al-Si alloy has been utilized as a base material to prepare the composite materials along with graphite powder. Fabricated materials have been characterized and evaluate the effect of rolling at moderate temperature on mechanical and physical properties. It has been found that the composite's material hardness have significant with respect to rising thickness reduction. The density of the materials continuously increases with increasing the percentage of thickness reduction and porosity reduced.

Effects of Si and SO2 on Corrosion of Fe–20Cr and Fe–20Cr–20Ni Alloys in Reducing Waste Combustion Gases

Model alloys, Fe–20Cr and Fe–20Cr–20Ni (wt%) with and without 1% Si, were exposed to four different gas mixtures Ar–10H2O, Ar–10H2O–0.1HCl, Ar–10H2O–0.1HCl–10CO2, Ar–10H2O–0.1HCl–10CO2–0.5SO2 (vol.%) at 650 °C. The Fe–20Cr and Fe–20Cr–20Ni alloys underwent breakaway corrosion in Ar–10H2O–(0.1HCl)–(10CO2), forming Cr2O3 and Fe-rich oxide nodules. Silicon addition markedly increased corrosion resistance for both alloys by forming an additional SiO2 layer beneath the Cr2O3 scale. Addition of SO2 to Ar–10H2O–0.1HCl–10CO2 significantly suppressed the formation of Fe-rich oxide nodules on Fe–20Cr. Corrosion in the SO2-bearing gas resulted in (Cr, Fe, S)-rich precipitates in all alloys. The effects of gas composition and Si alloying on corrosion of both alloys are discussed in terms of transport processes within the scales.

Preparation of low residual silicon content Si-SiC ceramics by binder jetting additive manufacturing and liquid silicon infiltration

Complex silicon carbide (SiC) ceramic components are difficult to fabricate due to their strong covalent bonds. Binder jetting (BJ) additive manufacturing has the outstanding advantages of high forming efficiency and no thermal deformation, especially suitable for printing complex structure SiC components. This study tried to obtain low silicon content silicon carbide ceramics by binder jetting followed by phenolic resin impregnation and pyrolysis (PRIP) and liquid silicon infiltration (LSI). BJ was used for the SiC green parts fabrication, and the highest compressive strength (7.7 ± 0.3 MPa) and lowest dimensional deviations (1.2–1.6 mm) were obtained with the printing layer thickness of 0.15 mm. Subsequently, PRIP treatments were introduced to increase the carbon content for the following LSI process. As the number of PRIP cycles increased, the carbon density of SiC/C preform increased and the porosity decreased. After the LSI treatment, the final Si-SiC composites processed with 2 PIRP cycles reached the highest flexural strength (257 ± 14.26 MPa) and the best wear resistance. This was attributed to the low residual silicon content (10.2 vol%) and almost no residual carbon. Furthermore, several complex structural components were fabricated using these methods. The preparation of complex components verifies the feasibility of BJ and LSI for manufacturing high-strength and high-precision SiC ceramics. Besides, this work hopes to provide technical guidance for the preparation of complex SiC composites in the future.

Influence of Silicon Additives on Tribological and Rheological Test Results for Vegetable Lubricants.

This paper describes an investigation of the effects of silicone-containing additives on the tribological and rheological properties of various lubricant blends. Aerosil® and layered silicate were used to modify lubricants containing rapeseed, linseed and soy oil that were thickened with soap thickener. Tribological tests were carried out using a four-ball concentric contact tester. On the basis of the data obtained from the tribological studies of the selected lubricant blends, it was concluded that the addition of amorphous silica increased the anti-seizure and anti-wear properties of the tested lubricants. The addition of montmorillonite caused a significant increase in the values of the individual parameters determining the level of lubricating properties of the tested lubricants in comparison with the lubricants modified with the silica additive. Based on the results of the rheological tests of the studied lubricants, it was found that the applied additives caused a change in the dynamic viscosity and chemical structure of the tested lubricants, expressed by a change in the values of the G' and G″ indices. The main finding of this manuscript was to demonstrate that the use of montmorillonite and aerosil additives improves the functional properties of vegetable-based plastic lubricants. The performance of tribological and rheological tests is of great scientific importance, as it provides an insight into the interaction of siliceous additives with the results of tribological tests on vegetable-oil-based greases. These findings make it possible to determine the behaviour of the lubricant under load and add to the knowledge of vegetable greases.

Effect of Natural and Artificial Silicon Additives on the Physicomechanical Performance of Dolomite-based Alkaline-Activated Mortar

Effect of Natural and Artificial Silicon Additives on the Physicomechanical Performance of Dolomite-based Alkaline-Activated Mortar

Effect of chromium and silicon additions on the hot corrosion resistance of nickel aluminide coatings

The effects of chromium and silicon modification on the microstructure and hot corrosion resistance of slurry aluminide coatings applied on pure nickel was studied by in-depth microscopic analyses. The simple and the Cr-modified aluminide coatings provided limited protection in Type II hot corrosion conditions but the Si-modified coating exhibited outstanding resistance with no sign of attack after 300 h of isothermal exposure at 700 °C. The synergistic dissolution between NiO and Al2O3/Cr2O3 appears responsible for the onset of the corrosion attack for the simple and Cr-modified coatings while silicon is shown to extend the incubation period.

"Comparative Evaluation of Three Different Microabrasion Techniques in Esthetic Management of Fluorosis": An In Vivo Study.

"Comparative evaluation of three different microabrasion techniques in esthetic management of fluorosis"-an in vivo study. A total of 48 permanent incisors in children between the age-groups of 8-12 years with Dean's fluorosis index modified criteria 1, 2, and 3 were included. The patients were randomly divided into three groups; each group included 16 samples. Group I-phosphoric acid and pumice microabrasion (37% phosphoric acid and pumice as abrasive), group II-opalustre microabrasion [6.6% hydrochloric (HCL) acid and silicon dicarbide (SiC2)], and group III-icon etch microabrasion (15% HCL acid gel as icon etch, pumice, and resin infiltrate). Preoperative sensitivity and pulp vitality of each tooth were evaluated. Standardized preoperative photographs were captured for the evaluation of color parameters L1, a1, and b1 by Adobe Photoshop 7 software and an assessment of color enhancement was carried out. Preoperative surface roughness was evaluated with two methods like, cellulose acetate replicating tape and confocal microscope, and Epoxy resin replica obtained from the preoperative impression of teeth using additional silicone and contact profilometer. Microabrasion was done accordingly. Postoperative values of all the parameters were evaluated. Phosphoric acid and pumice showed the best color change, followed by icon etch resin infiltrate. Opalustre (6.6% HCL acid and SiC2) and was unsuccessful as it had less concentration and was more abrasive. Phosphoric acid and pumice showed the best color enhancement, followed by icon etch resin infiltrate and opalustre. Icon etch resin infiltrate showed minimal surface roughness followed by phosphoric acid and pumice and opaluster group. Reddy VN, Nagar P, Lakhotia R, et al. "Comparative Evaluation of Three Different Microabrasion Techniques in Esthetic Management of Fluorosis": An In Vivo Study. Int J Clin Pediatr Dent 2023;16(4):572-581.

Silicon improves the growth of Glycyrrhiza uralensis Fisch. under salt and/or drought stress by regulating respiration metabolism

Drought and salt stress severely threaten the growth and productivity of Glycyrrhiza uralensis Fisch. (G.uralensis), and usually, they occur concomitantly. Silicon (Si) addition is well known to enhance the tolerance of plants. Here, we analyzed the changes in parameters related to growth and respiration, including glycolysis pathway (EMP), tricarboxylic acid (TCA) cycle, and pentose phosphate pathway (PPP) by Si in G. uralensis seedlings under salt and/or drought stresses. Results showed that Si effectively alleviated the effect of salt, drought and combined stress on the growth and respiration metabolism of G. uralensis seedlings. Under salt stress, Si increased leaf number by 15.13%, upregulated the TCA pathway at the transcriptional level, and increased PFK, PK, and content of acetyl CoA in both aerial and underground, ICDHm, α-KGDH in aerial part and NAD-MDH in underground part, thus alleviating the inhibitory effect of salt stress on the EMP–TCA process, but weakening the PPP by declining G6PDH and 6-PGDH in aerial part by 34.10% and 55.54%, and G6PDH in underground part by 83.86%. Under drought stress, Si increased underground biomass by 11.40%, slowed the EMP by decreasing PFK in aerial part by 21.76%, PK and PFK in underground part by 38.11% and 64.71%, weakened PPP by reducing 6-PGDH in aerial part by 72.9%, G6PDH and 6-PGDH in underground part by 77.00% and 64.71%. Si increased SDH and phosphoenolpyruvate carboxylase (PEPC) by 28.66% and 145.48% with the TCA cycle and GABA shunt as the main respiratory pathways in the underground part of drought-stressed seedlings. Under combined stresses, Si addition increased leaf number and aboveground biomass by 11.96% and 23.88%, upregulated the EMP and TCA pathways at the transcriptional level, and alleviated the effects of combined stress on EMP–TCA metabolic processes at the physiological and biochemical levels by increasing PDH, α-KGDH and NAD-MDH in aerial part by 27.22%, 18.85% and 140.37%, HK, PK and PEPC in underground part by 93.97%, 25.81% and 31.19%, initiated the replenishment mechanism and inhibited GABA shunt in underground part of G. uralensis to provide energy for vital activities. In conclusion, Si can effectively regulate respiration metabolism process to provide more substrates for subsequent physiological processes, thus improving tolerance to salt and drought stress, and thereby promote the growth of G. uralensis seedlings under stress conditions.

Impact of Silicon Addition on the Development of Gelled Pork Lard Emulsions with Controlled Lipid Digestibility for Application as Fat Replacers.

Pork lard gelled emulsions stabilized with two proteins [soy protein concentrate (SPC) or a pork rind protein extract (PRP)], both with and without added silicon (Si) from diatomaceous earth powder, were gelled by microbial transglutaminase and к-carrageenan. These gelled emulsions (GEs), intended as fat replacers, were evaluated in different aspects, including microstructure and technological properties during chilling storage. In addition, in vitro gastrointestinal digestion (GID) with an analysis of lipolysis and lipid digestibility was also evaluated. All GEs showed adequate technological properties after 28 days of chilling storage, although the SPC-stabilized GEs showed better gravitational and thermal stability (~4% and ~6%, respectively) during chilling storage than the PRP-stabilized ones (~8 and ~12%, respectively). PRP developed larger flocculates restricting pancreatic lipase-mediated lipolysis during intestinal digestion. The addition of Si to both GE structures protected them against disruption during in vitro digestion. Accordingly, Si appears to slow down fat digestion, as reflected by higher triacylglycerides content after GID (15 and 22% vs. 10 and 18% in GEs without Si) and could become a potential candidate for use in the development of healthier meat products.

Fluid-structure interactions of peripheral arteries using a coupled in silico and in vitro approach

Vascular compliance is considered both a cause and a consequence of cardiovascular disease and a significant factor in the mid- and long-term patency of vascular grafts. However, the biomechanical effects of localised changes in compliance cannot be satisfactorily studied with the available medical imaging technologies or surgical simulation materials. To address this unmet need, we developed a coupled silico-vitro platform which allows for the validation of numerical fluid-structure interaction results as a numerical model and physical prototype. This numerical one-way and two-way fluid-structure interaction study is based on a three-dimensional computer model of an idealised femoral artery which is validated against patient measurements derived from the literature. The numerical results are then compared with experimental values collected from compliant arterial phantoms via direct pressurisation and ring tensile testing. Phantoms within a compliance range of 1.4–68.0%/100 mmHg were fabricated via additive manufacturing and silicone casting, then mechanically characterised via ring tensile testing and optical analysis under direct pressurisation with moderately statistically significant differences in measured compliance ranging between 10 and 20% for the two methods. One-way fluid-structure interaction coupling underestimated arterial wall compliance by up to 14.7% compared with two-way coupled models. Overall, Solaris™ (Smooth-On) matched the compliance range of the numerical and in vivo patient models most closely out of the tested silicone materials. Our approach is promising for vascular applications where mechanical compliance is especially important, such as the study of diseases which commonly affect arterial wall stiffness, such as atherosclerosis, and the model-based design, surgical training, and optimisation of vascular prostheses.

Shade selection for natural tooth color replication on porcelain laminate veneers

The final color of dental ceramics depends on different factors such as light source, substrate, and selected material (thickness, contour, and texture). Objective: To report a clinical case in which a predictable protocol is used to optimize the final color of porcelain laminate veneers. Case report: A male patient attended the dental clinic dissatisfied with the composite resin restorations made on his upper anterior teeth. After anamnesis and clinical examination, it was suggested that the resin restorations be replaced by laminated porcelain veneers. A diagnostic wax-up was performed. The mock[1]up was also used to evaluate the aesthetic length for replicating the details of the incisal edge and the shape and size of the embrasures. The shade was selected before composite resin removal to avoid dehydration of the dental substrate. A photograph was taken to guide the selection of colors in different thirds. After removing the restorations, another photograph was taken to evaluate the color of the substrate. The impression was taken with 000 retractor wire and addition silicone. The laminates were made with pressed ceramic and feldspathic porcelain veneers were subsequently applied by layering the layers of dentin, incisal edge and enamel based on the waxing diagnosis. After approval by the patient, a conventional cementation technique was performed. The occlusal adjustment was made with rubber polishing cups and the anterior and lateral guides were checked. Conclusion: The protocol recommended for successful selection of the color of a porcelain laminate relies on the combination of knowledge of concepts, resources such as shade guides, spectrophotometers, and photographs, and porcelain application and characterization techniques performed by the technician and luting techniques by the dentist.

Direct current arc quenching performance of a model electric fuse equipped with SiO2 sand and additive silicone resin as an arc quenching medium: the effect of a vaporized silicone decomposition mixture on transient arc resistance

Most high-power electric fuses installed in DC distributions of automobiles employ silica sand (chemical formula SiO2) as arc quenching material to implement the limitation and subsequent interruption of high direct currents. This paper on arc quenching material describes the effects of the addition of silicone resin (chemical formula C2H6SiO) on SiO2 sand, based on the resistance of an arc discharge in SiO2 vapor mixed with silicone resin vapor. The measurement results obtained for the fuse operation of a model electric fuse show that the addition of silicone resin, e.g. an even coating of silicone resin on the surface of a Cu fuse element, attains a shorter arc quenching time. This phenomenon is subsequently explained based on the rise effect of an arc column resistance achieved by mixing with silicone vapor decomposition. The chemical compositions of high-temperature SiO2 vapor mixed with C2H6SiO vapor decomposition are evaluated to show the predominant chemical species at 30 000 K–5000 K for several C2H6SiO vapor concentrations, . The results obtained for of 10%–50% reveal that a H atom originating from C2H6SiO is present at high molar fractions above 0.1 over a wide temperature range of 12 000 K–5000 K. Further evaluations of the electrical resistivity for the high-temperature vapor show that mixing with C2H6SiO vapor contributes to a rise in at temperatures of 10 000 K–6000 K. A contribution analysis of the reveals that the rise effect of the is accomplished chiefly by the presence of a H atom that has dissociated from C2H6SiO.

Pre-Lithiation Strategy on Graphite-Silicon Diffusion-Dependent Electrode for High-Performance All-Solid-State Batteries

All-solid-state batteries (ASSBs) have emerged as promising next-generation energy storage devices due to their low fire risk and high potential for high energy density. Solid electrolytes with low flammability can reduce safety concerns about fire/explosion incidents under abnormal conditions. More importantly, high energy density can be achieved using active materials with high specific capacities, such as Li metal, Si, or Ni-rich cathode material. In order to maximize the energy density of ASSBs, the electrode thickness should be reduced while increasing the areal capacity of the electrode. In this regard, graphite-silicon (Gr-Si) diffusion-dependent electrodes (DDEs) have tremendous advantages. The intra- and inter-diffusion-based Li+ transfer in DDE does not require additional SEs to form Li+ conduction pathways within the electrode. The absence of SEs in the electrode has a significant advantage in terms of volumetric and gravimetric energy density. Moreover, the addition of silicon, which has remarkable volumetric capacities, effectively reduces the thickness of the DDE while maintaining the areal capacity high. Reducing the thickness of the DDE not only dramatically increases the volumetric energy density, but also shortens the diffusion length within the electrode, enabling rapid charge/discharge. Due to their outstanding advantages, the Gr-Si DDE has attracted much attention as a promising electrode for ASSBs with high energy density. Regardless of aforementioned advantages, the Gr-Si DDEs suffer from irreversible capacity loss at the first charge/discharge cycle due to the low first coulombic efficiency (C.E.) (< 80 %) of Si. Furthermore, Si undergoes extreme volume changes of over 400% during charge/discharge cycling. This huge volume change during cycling causes the cracking and pulverization of Si particles, leading to increased internal resistance, the isolation of the active materials, and the significant structural collapse of the electrode.Thus, in this work, we propose a new pre-lithiation strategy on Gr-Si DDE for high-performance ASSBs. Pre-lithiation is an effective method to alleviate the problems of Si. The Li+ in the Gr-Si electrode lithiated by pre-lithiation can compensate for the irreversible capacity loss at the first charge/discharge cycle and improve the low first C.E. of the Gr-Si electrode. Furthermore, it can mitigate the volume expansion concerns such as Si pulverization and electrode structure degradation, since the pre-volume expansion can alleviate the extreme volume expansion of Si during cycling. By applying this powerful technique to Gr-Si DDE, we could realize ASSBs with high efficiency, high stability, and high performance. When the pre-lithiated Gr-Si DDE was applied to ASSBs, it showed higher first C.E. than the cell with Gr-Si DDE without pre-lithiation. Moreover, the cell with pre-lithiated Gr-Si DDE has high resistance to electrochemo-mechanical degradation, which comes from continuous and extreme volume changes at the electrode during charge/discharge cycling. The cell with pre-lithiated Gr-Si DDE exhibited excellent capacity retention of 85 % after 0.5 C charge/0.5 C discharge 200 cycles, while the cell with Gr-Si DDE only showed capacity retention of 65 %. Our pre-lithiation strategy effectively enhanced the efficiency and stability of high-performance Gr-Si DDE, and we believe that our approach can contribute to the commercialization of ASSBs with high energy density.J. Y. Kim, J. Park, M. J. Lee, S. H. Kang, D. O. Shin, J. Oh, J. Kim, K. M. Kim, Y.-G. Lee, Y. M. Lee, ACS Energy Letters 2020, 5, 2995.J. Y. Kim, S. Jung, S. H. Kang, J. Park, M. J. Lee, D. Jin, D. O. Shin, Y.-G. Lee, Y. M. Lee, Advanced Energy Materials 2022, 12, 2103108.J. Y. Kim, S. Jung, S. H. Kang, M. J. Lee, D. Jin, D. O. Shin, Y.-G. Lee, Y. M. Lee, Journal of Power Sources 2022, 518, 230736.

Addition Silicone Impressions in Fixed Prosthodontics: Clinical Standpoints.

Addition silicones have revolutionized the field of fixed prosthodontics because of their dimensional stability, sufficient tear strengthand excellent detail reproduction. This review study aims to provide a detailed description of the essential variables to be taken into account during the process of making addition silicone impressions in fixed prosthodontics. These variables include the selection of appropriate tray type, size, and fabrication; the use of tray adhesive; gingival displacement techniques; manipulation of the impression material; the choice of the impression material's viscosity; impression techniques; and the proper insertion, removal, disinfection, and pouring of the cast. Additionally, this review aims to help doctors produce high-quality impressions by empowering them to critically assess the impressions to spot mistakes and motivating them to redo impressions that have serious problems before submitting them to the laboratory.

Morphology evolution and agglomeration mechanism of Fe5Si3 precipitated phase after Fe[sbnd]Si microalloying and its effect on the properties of brasses

The regeneration of scrap brass is affected by the impurity elements in raw materials. It is of practical significance to clarify the interaction of trace elements in brass melt for efficient recovery of scrap brass. The effect of FeSi microalloying on microstructure evolution and properties of as-cast H62 brass was investigated in the present study. The experimental results indicated that the microstructure of H62 brass containing 0.4 wt% Fe changed obviously after the introduction of silicon element. The volume fraction of Fe-rich phase increased with the increase of Si content, and the introduction of Si intensified the agglomeration behavior of Fe-rich phase. The thermodynamic analysis indicated that the silicon showed strong reactivity and bonding ability, and theoretical calculation suggested that silicon preferentially bonded with iron in melt to form new atomic clusters. The introduction of silicon also changed the morphology of the precipitated phase. The influence of silicon addition on the morphology evolution of FeSi precipitated phase was studied. The above reasons should be responsible for the microstructure evolution of as-cast brass. In addition, the mechanical properties and electrical conductivity of the microalloyed brass were tested. This study provides a new insight into the regulation of microalloying elements in regenerated brass.

An In Vitro Comparative Study of Maxillary Denture Base Retention Between Conventional Fabrication and 3D Printed Techniques

Objective: Many researchers have attempted to assess 3D printing as a manufacturing method to be used as an alternative for theconventional means. The current study aimed to determine the feasibility of 3D printed complete dentures in terms of retention.Methods: An edentulous maxillary model with an overlaying layer of mucosa was fabricated by 3D printing, using two different resinsfor the mucosa and model, which were then glued together to establish the final model. Afterwards, 8 single step putty and washimpressions were recorded with addition silicone. Each impression was scanned with a laboratory scanner. From each impression astone cast was fabricated on which a conventional baseplate was constructed by heat polymerized PMMA with the pack and presstechnique. Meanwhile, from the 8 STL files of the scanned impressions, 8 baseplates were designed and printed with the denture baseresin. Next, each of the 16 baseplates were connected to a loop at their center. Finally, the retentive value of all baseplates was measured by means of the universal testing machine. A statistical analysis was performed to evaluate the significance of retentive difference between the two groups.&#x0D; Results: The statistical analysis revealed that the printed dentures were significantly more retentive than the conventional, with a p-value of less than 0.029 and mean values of 15.0462 N and 12.05 N respectively.&#x0D; Conclusions: This study concluded that 3D printed complete dentures were significantly more retentive than the conventionallyfabricated dentures.

The Effect Addition of (Silicon and Silver) and Heat Treatments to the Alloy Properties (Copper - Nickel - Tin)

Copper-Nickel-Tin alloys have been recently developed by Hardening due to spinodal decomposition. The (Cu - 9Ni - 6Sn) system has shown promise in this direction and has been used to develop several high strength compositions. It is well known the fact that small element additions significantly modify phase transformation characteristics, the effect of adding Silicon or Silver on the Spinodal hardening in (Cu - 9Ni - 6Sn) alloy was studies close to the Spinodal cusp temperature. The presence of Silver also increased the ductility of alloy at the expense of some hardness. The effects of trace elements additions have been observed in this work with a view to improve high strength alloys as substitutes to the Copper – Beryllium alloys. The results obtained from the current research proved that adding a small amount of alloying elements with a percentage (1%) of silicon or silver to the base alloy (Cu - 9% Ni - 6% Sn), led to the stability of the mechanical properties resulting from the stability of the microstructure due to Heat treatment for hardening (Spinodal decomposition).

Effect of Si on the evolution of plasticity mechanisms, grain refinement and hardness during high-pressure torsion of a non-equiatomic CoCrMnNi multi-principal element alloy

The present study unraveled the defining role of small silicon (Si) addition (5 atomic %) in dramatically altering the plasticity mechanisms, grain refinement and hardening response of a non-equiatomic CoCrMnNi multi-principal element alloy (MPEA) during high-pressure torsion (HPT) processing. Both the Si-free and the Si-added MPEAs had a face-centered cubic (FCC) structure and were subjected to a quasi-constrained HPT processing at 6 GPa pressure to different number of turns (0.5 and 5). Microstructure evolution was studied at the center and edge of the HPT-processed discs using X-ray diffraction line profile analysis (XLPA) and transmission electron microscopy (TEM). Si addition altered the predominant plasticity mechanism from micro-band formation to extensive occurrence of nano-twinning at the early stage of HPT processing. At later stages of HPT processing, both alloys exhibited deformation twinning but its propensity was considerably higher for the Si-added MPEA, as revealed by ∼50% higher twin fault probability. Additionally, the Si-added MPEA showed ∼30% higher dislocation density at any given stage of HPT processing compared to the Si-free MPEA. A significantly accelerated nano-structuring coupled with a finer saturation grain size was observed in the Si-added MPEA (34 nm for Si-free versus 23 nm for Si-added). These effects can be explained by the influence of Si addition on lowering the stacking fault energy (SFE) (from ∼40 mJ/m2 in Si-free to ∼20 mJ/m2 in Si-added MPEA) and increasing the solute pinning effect of Si on lattice defects. The plasticity mechanisms at nano-scale were also influenced by the presence of Si as confirmed by the formation of nano-twins and stacking faults inside the nano-grains for the Si-added and Si-free MPEAs, respectively. The differences in plasticity mechanisms and microstructure evolution resulted in enhanced hardness in the early stages of HPT processing for the Si-added MPEA, but the difference in hardness between the two alloys tended to be reduced at higher strains.

Microstructure and Mechanical Properties of Al-Si Alloys Produced by Rapid Solidification and Hot Extrusion.

The paper presents the results of tests of rapid solidification (RS) aluminum alloys with the addition of silicon (5%, 11%, and 20%). Casting by melt-spinning on the surface of an intensively cooled copper cylinder allowed to obtain a metallic material in the form of flakes, which were then consolidated in the process of pressing and direct extrusion. The effect of refinement on structural components after rapid solidification was determined. Rapidly solidified AlSi materials are characterized by a comparable size of Si particles, regardless of the silicon content, and the shape of these particles is close to spheroidal. Not only Si particles are fragmented, but also the Al-Si-Fe phase, which also changed its shape from irregular with sharp edges to regular and spherical. The melt-spinning process resulted in a fine-grained structure compared to materials obtained by gravity-casting and extrusion. The influence of the high-temperature compression test on the mechanical properties of rapidly solidified materials was analyzed, and the results were compared with those of gravity-cast materials. An increase in strength properties was found in the case of the AlSi5 RS alloy by 20%, in the case of AlSi11RS by 25%, and in the case of the alloy containing 20% Si by as much as 86% (tensile test). On the basis of the homogeneity of the particle distribution determined by the SEM method, it was found that rapid solidification is an effective method of increasing the strength properties and improving the plastic properties of Al-Si alloys.