Increasing Si Content Research Articles

The new nanocapsule structure and cyclic tribological properties of Mo2N/Ag/Si3N4 nanocomposite film

Nanostructured films present versatile properties in the area of friction. This paper introduced a adaptive nanostructured film with multiple cycle service capability. Based on the concept of capsule sustained-release, a series of Mo2N/Ag/Si3N4 composite films with different Si contents were prepared. The results show that the films were mainly composed of fcc-Mo2N, fcc-Ag and Si3N4, presenting a “capsule structure” with the encapsulation of Mo2N/Ag by Si3N4. The crystalline Si3N4 wrap the Mo2N to form a co-extended growth structure, when the Si content is lower than 6.3 at. %. However, the coherent interface could be destroyed for the film with higher content of Si (>6.3 at. %), owing to the transforming to an amorphous phase of Si3N4. When annealed at 500 °C, the growth of Ag content on the surface is higher for film with 6.3 at. % Si than that of film with 11.4 at. % Si, indicating that the capsule structure with amorphous Si3N4 can hinder the diffusion of Ag. With the increase of Si content, the hardness of the film increases firstly and then decreases gradually. The maximum hardness value of 34.3 GPa can be obtained for the film with 6.3 at. % Si. The average friction coefficient of Mo2N/Ag/Si3N4 composite films with 6.3 and 11.4 at.% Si contents decreased from 0.48 to 0.33 and from 0.42 to 0.31 respectively with the increase of friction temperature from 200 °C to 700 °C under friction test. At the same temperature, the friction coefficient for film with 6.3 at.% Si is always lower than that of film with 11.4 at.% Si, but the wear rate is always slightly higher. The temperature-cycling friction times of nanocomposite films consisting of amorphous Si3N4 capsule structure with11.4 at.% Si is twice that of crystalline Si3N4 with 6.3 at % Si. The amorphous “capsule” structure can improve the multi-cycle serviceability of the film.

Development of FeSi steel with increased Si content by laser powder bed fusion technology for ferromagnetic cores application: Microstructure and properties

Additive manufacturing technology like laser powder bed fusion represents a valid alternative for the production of ferromagnetic cores. In this study, two grades of steel were considered, with standard (3.0 wt%) and high (6.5 wt%) Si content. The study is aimed at optimizing the process parameters in order to obtain components suitable for magnetic applications. Moreover, the effect of post-production annealing heat treatment on the microstructure evolution is investigated. The investigation included microstructural analysis by optical microscope, dynamic scanning calorimetry analysis and electro-magnetic measurements on samples with optimized geometry. Results shows that both types of steel can be produced free from defects. Even if the magnetic behaviour of FeSi6.5 samples by AM do not fully reproduces that obtained on electrical steels manufactured by standard process, it appears quite promising. In this framework the optimization of post-production processes represents a promising challenge to meet market demands.Graphical abstract

Study of the anomalous behavior of the a-HFO2 refractive index with increasing Si doping by quantum molecular dynamics simulation

This paper provides an atomistic exploration of amorphous composite HfO2-SiO2 oxides to explain the experimentally observed anomalous behavior of the refractive index with increasing Si content. We use an approach to obtain amorphous states of high-temperature oxides by melting–quenching the initial HfO2 crystal containing various amounts of Si impurities. The calculations are carried out by quantum molecular dynamics. The coordination numbers of Hf, Si, and O atoms are studied at various doping levels. The change in the atomic structure of a-HfO2 depending on the doping level qualitatively explains the anomalous behavior of the refractive index.

Corrosion behavior and passive film characteristics of AlNbTiZrSix high-entropy alloys in simulated seawater environment

The corrosion and passive behavior of AlNbTiZrSix high-entropy alloys (HEAs) with different Si contents were investigated in simulated seawater environment at room temperature. The results showed that the average grain size decreased with an increase in Si content, which was associated with the inhibiting effect on grain growth due to the precipitation of Zr5Al3 phase. The passive film of the HEAs primarily consisted of TiO2, Nb2O5, and ZrO2. Preferential corrosion occurred in Zr5Al3 phase regions, and the addition of Si reduced passive film stability, worsening corrosion resistance.

Effect of Si content on the microstructure and properties of CrSi coatings for ATF cladding

Microstructure, mechanical properties, corrosion resistance and high-temperature oxidation resistance of four CrSi coatings with different Si content ranging from 0 at% to 67 at% were investigated. With increasing Si content from 11 at% to 67 at%, the main forms of Si exist the coatings were detected to be Cr3Si, Cr5Si3 and CrSi2, respectively. All the CrSi coatings own higher nano-hardness due to the formation of intermetallic. For Si content ≤33 at%, the CrSi coatings showed good corrosion resistance in static pure water of high temperature and pressure. However, the higher Si content (67 at%) led to the dissolution of Si in the form of [Si(OH)]4, as well as insufficient Cr to form a continuous Cr2O3 layer. The high-temperature oxidation tests showed that the coating with 11 at% Si content exhibited the best oxidation resistance than other coatings, due to the formation of outermost Cr2O3 layer, stable Cr3Si phase and inner Zr2Si. Our study indicates that the coating with 11 at% Si content displays good comprehensive properties and could be used as a candidate material for ATF coatings.

Strength-ductility synergy through tailoring heterostructures of hot-rolled ferritic-martensitic steels containing varying Si contents

By utilizing the feature that adding Si is able to effectively increase Ac1 and Ac3 temperatures of ferritic-martensitic (FM) steels, four FM steel sheets with different Si additions (0–1.0 wt%) were prepared by hot rolling at the same intercritical temperature to obtain various heterostructures. Their mechanical properties were evaluated and well correlated with detailed microstructural characteristics revealed by multiple characterization methods. Results show that the 0 Si specimen has a nearly complete martensitic structure; the 0.4 Si specimen consists of ∼23.5 vol% island-like ferrites embedded in martensites exhibiting a typical bi-modal structure (BMS); the 0.7 Si specimen consists of ∼46.8 vol% lamellar ferrites alternating with lamellar martensitic structures corresponding to a typical heterogeneous lamella structure (HLS); the 1.0 Si specimen is mostly comprised of ferrites no longer belonging to typical heterostructures. With increasing Si content, sizes of martensitic laths gradually decrease while the ferritic grains are coarsened. The 0.4 Si and 0.7 Si specimens exhibit high values (∼17 GPa%) of the product of ultimate tensile strength (UTS) and total elongation (TE), demonstrating a good strength-ductility synergy. Comprehensive analyses reveal that the 0.4 Si specimen with BMS exhibits a considerable hetero-deformation induced (HDI) strengthening effect, facilitating the production of the highest UTS (1476.3 MPa), while the 0.7 Si specimen with HLS shows a stronger HDI strain hardening effect leading to a higher TE (12.5%). This study could offer an important reference for designing and processing of FM steels with excellent strength-ductility synergy.

Structural and tribological properties of TiSiN films with different Si content

TiSiN thin films were deposited on 52100 steel and Al2024 substrates by magnetron sputtering method using Ti and Si targets in Ar+N2 atmosphere. Power values of 40 W, 60 W, and 75 W were applied to the Si target, while the voltage was constant at 370 V for the Ti target. The Si atomic ratios within the film's structure were found to vary in accordance with the increasing Si target power. The impact of varying Si atomic ratios on the structural, mechanical, and tribological properties of the films was investigated. X-ray diffraction, scanning electron microscopy, hardness and wear test methods were performed. As the Si ratio increased from 10 at. % to 20 at. %, the maximum hardness value was 6.06 GPa for 52100 steel and 4.33 GPa for Al2024. With increasing Si content, the film thickness increased from 1.63 µm to 2.05 µm. The lowest surface roughness of the produced films was 0.069 for 52100 steel and 0.308 for Al2024. The lowest wear rate of TiSiN film was calculated at 1.63 × 10−4 mm3/(N.m).

Effect of Si, Co, Fe contents and cooling condition on the microstructure of Al–Si–Co(–Fe) alloys

In this paper, several Al–Si–Co and Al–Si–Co–Fe alloys were prepared by varying the contents of Si, Co and Fe, solidified via fast and slow–cooling conditions. In the ternary Al–xSi–yCo (x = 6, 12, 18; y = 2, 4) alloys, the Co–rich phase is Al9Co2–type with a certain Si content, which can be marked as (Al,Si)9Co2. The Al9Co2–type phase exhibits developed dendrites and block–like morphologies under fast and slow cooling conditions, respectively. In the quaternary Al–xSi–4Co–yFe (x = 6, 12, 18; y = 2, 4) alloys, the formed intermetallic compound is Al13Fe4–type, containing a certain amount of Si and Co. It exhibits fine and coarse dendritic morphologies under fast and slow–cooling conditions, respectively. With the increase of Si content and Fe: Co ratio in the Al–xSi–4Co–yFe alloys, the Si content and Fe: Co ratio in the Al13Fe4–type phase increase synchronously. The hardness of Al–xSi–4Co–yFe alloys were tested, and it was found that the fast–cooling alloys have higher hardness than the slow–cooling ones, while the value of fast–cooling Al–12Si–4Co–4Fe alloy is the highest. Besides, comparing with Al9Co2, the Al13Fe4 phase has a much higher tendentiousness to precipitate from Al–Si–Co–Fe alloys. This work may be referred for the control of Co– and Fe–rich phases in Al–Si alloys, with the concept of altering element contents and solidification conditions.

In-situ formed SiC whisker strengthening of silicon carbide reticulated porous ceramics based on 3D printed lattices template

The SiC reticulated porous ceramics (RPCs) fabricated via sponge replica method usually showed a poor thermal shock resistance due to their randomly distributed skeleton structure and hollow struts. The present work reports a simple approach to prepare SiC RPCs with 3D lattices structure using the replica of printed resin, followed by pre-heated in coke bed and vacuum infiltration. The increased Si content and flake graphite addition promoted the formation of SiC whiskers network structure on the surface and matrix of SiC preform after pre-heated at 1400 °C. As SiC preforms were applied by vacuum infiltration and sintering, the three-layer struts included dense coating, SiC skeleton layer and filling layer were generated. Furthermore, in-situ SiC whiskers eliminated the coating cracks, also optimized the microstructure of the SiC matrix, thereby enhancing the thermal shock resistance and strength of SiC RCPs, whose strength increased from 0.36 MPa to 1.53 MPa, also the residual strength retention rate increased from 0 % to 75.2 % after three cycles of water- quenching.

Synergistic Effect of Alloying on the Strength and Ductility of High Carbon Pearlitic Steel

In this work, the effects of the micro-alloying of Mn, Ni, and Si on the microstructure and mechanical properties of high-carbon pearlite steels were investigated. The results indicated that the addition of solely Ni to high-carbon pearlitic steel can enhance the strength through the refinement of interlamellar spacing, but work-hardening in the ferrite of the pearlite colony may be delayed, leading to a reduction in area. The multiple additions of Ni and the increase in Mn and Si contents in high-carbon pearlitic steel were beneficial to obtaining a balance between ultimate tensile strength and reduction in area. Three-dimensional atom probe tomography results showed Si partitioning into ferrite and Mn and Ni elements partitioning into cementite. The addition of Si inhibited the formation of a continuous network of grain-boundary cementite, leading to high strength and high ductility through optimization of the microstructure.

Evolutions of Microstructure and Impact Toughness of Submerged Arc Weld Metal via Introducing Varied Si for Weathering Bridge Steel

In this paper, the influence of the silicon (Si) content on microstructure and impact property of submerged arc weld metals (WMs) for weathering bridge steel was clarified. Actual submerged arc welding (SAW) was carried out to produce WMs with 0.18 wt.%, 0.36 wt.%, 0.51 wt.%, and 0.60 wt.% of Si. The low temperature impact property of weld metal was detected, and the weld microstructures were characterized by optical microscopy (OM), scanning and transmission electron microscope (SEM and TEM), and electron backscatter diffraction (EBSD). The results indicate that WMs consist of polygon ferrite (PF), acicular ferrite (AF), granular bainitic ferrite (GBF), and martensite/austenite (M/A) constituents in each Si content. With increasing Si, the proportion of PF increased, while AF and GBF coarsened, the area fraction, fM/A, and the mean size, dM/A, of M/A constituents increased, the number of inclusions decreased, but the size increased. Further, the fraction of high-angle grain boundaries (HAGBs) with the misorientation tolerance angles (MTAs) greater than 15° reduced, while the mean equivalent diameter, MEDMTA≥15°, of ferrite grains with HAGBs increased. Accordingly, the impact toughness of WM was degraded from 108.1 J to 39.4 J with the increase in Si. The increase in M/A constituents and inclusions size reduced the critical fracture stress, thereby formation of larger microcracks and cleavage planes occurred. The reduced HAGBs exhibited a low hindering effect on crack propagation, and, consequently, the impact toughness decreased with increasing Si content.

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.

Microstructure and mechanical properties evolutions of 9Cr heat resistant steel deposited metals with different Si contents during 550 °C aging process

The stability of microstructure and mechanical properties of 9Cr heat resistant steel under high temperature and long term service conditions has been a hot issue of great interest. In the present study, the relationships between microstructure and mechanical properties evolutions of 9Cr heat resistant deposited metals with different Si contents (0.25 wt.% and 1.07 wt.%) at 550 °C aging for different times were investigated systematically. The results indicate that the degradation of mechanical properties during aging is mainly attributed to the coarsening of precipitates, transformation of precipitate types, decreasing of dislocation density and coarsening of martensite laths, and these factors are related to the Si content in the deposited metals and the aging time. It is worth mentioned that the sub-grain boundaries pinned by M23C6 forming after post weld heat treatment (750 °C/2.5 h) stabilize the tensile strength during aging. The recrystallization occurring after post weld heat treatment and high temperature aging is beneficial for the impact toughness but not for the strength. During aging process, the precipitate transformation follows the following sequence: M23C6→M6X→Laves phase. Moreover, the increase of Si content promotes the nucleation and coarsening of M6X, and then deteriorates the mechanical properties of the deposited metals.

Binary elements (Si, Mo) co-doping strategy enhanced the tribological performance of diamond-like carbon films

To overcome the constraints posed by high internal stress and weak bonding forces, and achieve DLC films exhibiting exceptional tribological characteristics. Si and Mo co-doped DLC (Si-MoDLC) films were fabricated via the double-target co-sputtering technology. The results revealed that Si was mainly present in SiC and SiO forms, while Mo existed mostly in MoC and Mo forms. With an increase in Si content from 0 to 14.4 ± 0.2 at.%, the ratio of sp3/sp2 (peak area ratio) increase from 1.2 to 2.1. The hardness decreased first and then increased, while the adhesion increased first and then decreased. The Si-MoDLC film with 3.4 ± 0.2 at.% Si and 7.7 ± 0.2 at.% Mo exhibited the lowest hardness (13.4 GPa) and the highest adhesion (340 mN). The tribological properties of thin films were significantly affected by Si content and the testing environment. In the air, the Si-MoDLC film containing 14.4 ± 0.2 at.% Si displayed the lowest friction coefficient (0.07) and a low wear rate (1.1 × 10−7 mm3/N·m), while in a methanol environment, it showed the highest friction coefficient (0.21) and wear rate (14.6 × 10−7 mm3/N·m). These findings provide valuable insights into the microstructure and properties of Si-MoDLC films and offer guidance for the application of DLC films in alcoholic environments.

The effect of Fe content on crystal phase and mechanical properties of 6061 aluminium alloy

In order to eliminate the adverse effects of impurity element Fe in aluminium alloy, the effects of Fe content on the microstructures and mechanical properties of 6061 aluminium alloy were studied utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and tensile testing machine. The results show that Fe exists mainly in α-AlFeSi and β-AlFeSi phases. Elemental Fe promotes the generation of fishbone shaped α-AlFeSi phase, while the percentage of needle shaped β-AlFeSi phase gradually decreases. After homogenizing annealing, the Mg2Si phase has been redissolved, and a large amount of Si element exists in the aluminium matrix. With the increase of Fe and Si content, β→α phase transition has been completed, and the fishbone α-AlFeSi phase accumulates at the grain boundary. After the extrusion forming process, the morphology of the α-Al12(MnFe)3Si phase changes from fishbone to granular, and the bulk deposition of α-Al12(MnFe)3Si improves the strength of 6061 aluminium alloy.

Insight into the role of Si on corrosion resistance of weathering steel in a simulated industrial atmosphere

This study investigates the role of Si on the corrosion resistance of weathering steel (WS) in a simulated industrial environment. With increasing Si content (0.15–0.50%), the corrosion resistance of WS is enhanced. On the one hand, the rust layer becomes compact and uniform because higher Si content promotes the formation of fine α-FeOOH. On the other hand, Si reacts with Fe3O4 to form a three-dimensional SiO2 network structure located around the cracks and holes of the rust layer. This structure has a protective effect, enhancing the corrosion resistance of WS and equipping the rust layer with self-healing functionality.

The effects of Si‐ion implantation and preoxidation on the corrosion behavior of a new steel SIMP in 550∘C ${\bf{55}}{{\bf{0}}}^{\circ }{\bf{C}}$ lead‐bismuth eutectic

AbstractTo improve the corrosion resistance of SIMP steel, we have investigated Si‐ion implantation and preoxidation effects on the corrosion behavior of SIMP steel samples, which have been in stagnant lead‐bismuth eutectic (LBE) with saturated oxygen at C for 1000 h. It was found that increasing Si content on the surface did not improve corrosion resistance performance. By contrast, the preoxidized sample demonstrated high resistance to LBE corrosion due to the presence of a thin Cr‐enriched oxide layer.

Infrared study of the structure of silicon oxynitride films produced by plasma enhanced chemical vapor deposition

The structure of thin (∼300nm) SiOxNy (0.23≤x≤1.95, 0.01≤y≤0.32) films produced by plasma enhanced chemical vapor deposition is studied by infrared (IR) spectroscopy. The dependence of the shape of the main IR absorption band in the range of 700–1400 cm–1 upon film composition is analyzed. The IR spectra exhibit strong overlapping of the bands corresponding to absorption on Si–O and Si–N bonds. A problem of separating these components is solved. Analysis of their relative intensities provides an insight into the film structure. The films with high oxygen content are found to have a homogeneous structure similar to that of nonstoichiometric Si oxide that can be described by the random bonding model. Increase of relative Si concentration and simultaneous decrease of oxygen and nitrogen content changes the film structure to the two-phase one obeying the random mixture model. Such material may be represented as a uniform mixture of interconnecting silicon–oxygen tetrahedra (Si–OaSi4-a, a=0..4) and silicon–nitrogen pyramids (Si3N). Relative Si concentration in the Si oxynitride films and their deposition temperature are hypothesized to play a decisive role on their structure, which is supported by thermodynamic modeling.

First-principles study on the electronic structure of siligraphene on a ZnO monolayer

Density functional theory was employed to investigate the electronic structures of atomic bilayer materials that form between graphene (g-C) or graphitic silicon carbide (also known as siligraphene: g-SiC and g-SiC2) and graphitic zinc oxide (g-ZnO). The results indicate that g-C/g-ZnO bilayers have semimetallic properties with an energy band gap of zero like in graphene. For a g-SiC/g-ZnO bilayer, an ensemble of three sp 2-hybridized carbon atoms periodically separated by three silicon atoms on g-ZnO has indirect and direct band gaps of 3.32 and 3.78 eV, respectively, which is suitable for use in light-emitting diode applications. For a g-SiC2/g-ZnO bilayer, an ensemble of four sp 2-hybridized carbon atoms periodically separated by two silicon atoms on g-ZnO has a direct band gap of 1.15 eV, which approaches the optimal value of the band gap (E opt ≃ 1.3 eV) for solar cell applications. The results show that increasing Si content in siligraphene can help to open the band gap of graphene and enhance the band gap of graphitic silicon carbide. The band gaps of siligraphene/g-ZnO bilayers depend on a smaller band gap from the monolayer component. Therefore, adjusting the Si content in siligraphene permits tuning of the band gap, and constructing a bilayer in the presence of a g-ZnO monolayer can slightly decrease the band gap. These results could lead to a new design of heterostructures with tunable band gaps for various applications.

Crystallization of Intermetallic Phases Fe2Si, Fe5Si3 for High Alloyed Cast Irons

This paper presents the results of laboratory tests related to high-alloy silicon cast iron (HSCI). These materials are corrosion-resistant and commonly used in cathodic protection systems as protective electrodes. Due to their high fragility, alloys with increased Si content are not suitable for producing elements exposed to dynamic loads. This paper analyzes the crystallization process of silicon alloys (with Si content between 23% and 25%) using thermal and derivation analysis methods. The tests also included an extended analysis of chemical composition. The metallographic tests included scanning electron microscopy with an EDS system, and the phase composition was determined using X-ray diffraction. As a result of the tests, the warp components were identified, the primary share of which are intermetallic phases of the Fe5Si3 type. Moreover, single silicon crystals were found. The test results allowed for clarification of the temperature range of the transition of the Fe2Si phase into the Fe5Si3 phase and the determination of characteristic points of the crystallization process (TSolidus i TLiquidus). Furthermore, bifilm-type inclusions were identified in the alloys. We also managed to present the silicon crystals and Fe5Si3 phases in a spatial layout via observation of the surfaces of contraction cavities using scanning electron microscopy.