Addition Of Si Research Articles

Study on the High-Temperature Oxidation of AlCrFeCoNi-Based High-Entropy Alloys with Trace Si Additions

This research investigates the isothermal oxidation behavior of AlCrFeCoNiSix (x = 0, 0.04, 0.08, 0.12at.%) at 900°C for 96hours from multiple aspects, including the oxidation surface, the oxide layer microstructure, and the oxidation mechanisms. The oxidation kinetics curves of the alloys follow the parabolic oxidation law. After 96hours of oxidation at 900°C, the oxide films of the AlCrFeCoNi and AlCrFeCoNiSi0.04 alloys are primarily composed of Al2O3. In contrast, the oxide films of the Si8 and AlCrFeCoNiSi0.12 alloys consist of an outer layer of Cr2O3/spinel oxides and an inner layer of Al2O3.The results show that the third element effect triggered by the addition of Si can promote the generation of an Al2O3 layer, which has a positive effect on the antioxidant of high-entropy alloys.

Analysis of coatings with Al and Si additives for high-temperature oxidation of steel

The article presents an analysis of the influence of aluminum (Al) and silicon (Si) coating additions on the process of high-temperature oxidation of steel. After high-temperature oxidation of coatings deposited on steel substrates, the oxidation was carried out in an air atmosphere at 800C for 20 hours. The samples were oxidized on one side, i.e. they were placed on a quartz plate during the test. After oxidation, the unit mass increase of the samples was measured using a laboratory scale with an accuracy of 0.00001 g. It was examined how the addition of these elements affects the formation of protective oxide layers that limit corrosion at elevated temperatures. Aluminum contributes to the formation of stable aluminum oxide (Al₂O₃) layers, while silicon supports the formation of silicon oxide (SiO₂). Both oxides act as protective barriers, reducing the penetration of oxygen into the material, which slows down its degradation. The appropriate concentration of these admixtures improves the steel's resistance to oxidation without significantly impairing its mechanical properties. The article emphasizes the importance of appropriate selection of Al and Si content to increase the durability of steel in high-temperature operating conditions.

DFT investigations of doping effects on the structural stability, thermal diffusion, and absorption/desorption kinetics in cubic, hexagonal, and monoclinic Mg2NiHx hydrides

The pseudo-potential plane-wave method, based on Density Functional Theory (DFT) and using the Generalized Gradient Approximation (GGA), is applied to investigate the effects of progressive hydrogen insertion on the structural stability and energetics of Mg2NiHx hydrides. The obtained results indicate that Mg2Ni crystallizes in the hexagonal (P6222) structure. Taking into account the site preference of H atoms, the progressive hydrogenation of Mg2Ni favors the formation of Mg2NiHx hydrides in cubic (Fm-3m) and monoclinic (C2/c) phases rather than the parent hexagonal phase. The alloying effects of Cu, Y, Si, Ti, Cr, and Fe on the structural stability and absorption/desorption kinetics of monoclinic Mg2NiH4 are also investigated. More particularly, systems with Cu and Si additions have the lowest desorption temperatures, as confirmed by Molecular Dynamic (MD) calculations. The thermal diffusion is well observed in all studied compounds. The corresponding average thermal diffusion coefficients are mainly attributed to hydrogen atoms and are increased by the addition of Cu. These trends are expected to have an important role in phase transitions observed during hydrogen insertion. The present study based on DFT and MD calculations shows that doped Mg2NiHx are promising hydrides with interesting kinetic behavior. The obtained results can be useful for future experimental studies devoted to improving hydrogen absorption/desorption temperatures, low energy costs, and high atomic hydrogen storage capacities in Mg2Ni.

Effects of micron-sized Si particles on the static and dynamic mechanical properties and fracture behavior of Al-xSi alloy sheets

In this paper, a comprehensive analysis was conducted on the effects of micron-sized Si particles on the microstructure, static and dynamic mechanical properties, and fracture behavior of wrought Al-xSi alloy sheets. The investigation employed techniques such as optical microscope, scanning electron microscope, laser scanning confocal microscope, transmission electron microscope, tensile testing and fatigue testing. The results show that when the Si content is below 12 wt%, the size of the Si particles in the alloy sheets does not exceed 3 μm, and their quantity gradually increases with higher Si content. As the Si content increases, the grain size of the alloy sheets is refined from 63 μm to 8 μm. The alloy strength initially increases and then slightly decreases with further Si addition. while elongation exhibits a general downward trend. The tensile fracture modes of Al-(1–12 wt%) Si alloy sheets are all ductile fractures. The fatigue life of Al-xSi alloy sheets first extends and then shortens as the Si content increases. With the increase of Si content, the yield strength of the alloy sheets gradually increases from 47.6 MPa to 85.7 MPa. When the Si content is 12 wt%, the tensile strength reaches the maximum value of 185.4 MPa. With the increase of Si content, the elongation of the alloy sheet first increases slightly, reaching 35.0 %, when the Si content increases to 15 wt%, the elongation gradually decreases to 17.5 %. As the Si content increases, the fatigue life of the alloy sheets gradually extends. When the Si content reaches 12 wt%, the alloy sheet achieves its maximum fatigue life, reaching 9.97 × 105–1.97 × 10⁶ cycles, approximately 11–14 times longer than that of the Al-1 wt% Si alloy sheet. However, with a further increase in Si content to 15 wt%, the fatigue life significantly decreases to 4.08 × 10⁵–4.70 × 10⁵ cycles, shortening by approximately 59–76 %. The fatigue crack source of Al-xSi alloy sheets gradually changes from the persistent slip bands on the surface of the sheet to the large-sized Si particles on the surface of the sheet. The functional relationship between the fatigue life of Al-xSi alloy sheets as the Si content changes is established, and the fatigue life influencing factor ISi is introduced to quantitatively describe the influence of the number of micron-sized eutectic Si particles on the fatigue life or fatigue properties of the alloy sheets. This study provides important scientific insights for optimizing alloy property and meeting diverse industrial demands, thereby promoting the application and development of wrought Al-Si alloy in broader fields.

Characterization of modified ZA alloys with Si addition

Characterization of modified ZA alloys with Si addition

Enhanced mechanical properties of lightweight refractory high-entropy alloys at elevated temperatures via Si addition

A new lightweight refractory high-entropy alloys were prepared by introducing Si element into AlMo0.5NbTiV alloy. The effects of Si content on microstructural evolution, density and high temperature mechanical properties were analyzed. The results show that the addition of Si leads to the formation of hard and brittle M5Si3-type (M = Ti and Nb) phase at the grain boundary of the matrix, which gradually transforms the alloys from a single body centered cubic (BCC) structure to a dual-phase structure. While the density of AlMo0.5NbTiVSix alloys decreases from 6.01 to 5.59 g/cm3 with the increase of Si content, and the mechanical properties are also significantly improved, AlMo0.5NbTiVSi0.5 alloy has the best yield strength of 1428 and 390 MPa at 1073 K and 1273 K, respectively. Among them, AlMo0.5NbTiVSi0.1 alloy has the best compression ductility strain at 1073 K, up to 22.2 %, indicating that the addition of appropriate Si can improve the compression ductility of the alloy, which is also caused by the combination of grain refinement and the appearance of eutectic structure. On the one hand, the segregation of Si elements at grain boundaries results in slow growth of the primary crystal, which inhibits the growth of grains. On the other hand, the eutectic structure composed of M5Si3 and BCC is distributed at the grain boundary, which is not conducive to the growth of grains, and the combined effect of the two eventually leads to the grain refinement. The strengthening mechanisms of the alloys can be attributed to the second phase strengthening, solid solution strengthening and grain refinement strengthening. In addition, the softening of the alloys at 1273 K is caused by dynamic recovery and dynamic recrystallization, and the dynamic recovery is the main softening mechanism.

Synergistic strengthening mechanism of Mg and Si on Cu-Fe alloys with high strength and high conductivity

In this study, high strength and conductivity Cu-Fe-Si-Mg alloys were produced by casting and multi-stage thermos-mechanical treatment (MTT). The electrical conductivity, yield strength, tensile strength and elongation of the Cu-2.5Fe-0.1Si-0.15 Mg alloys were 68.23 %IACS, 653 MPa, 692 MPa and 4.35 %, respectively. The addition of Mg was beneficial to reduce the generalized planar fault energy and increase the density of substructure. Meanwhile, there was a tendency for Mg atoms to segregate at the interfacial region where the second phase met the copper. The segregation of Mg effectively inhibited the growth of precipitates. There was a dramatic improvement in the ability of the second phase to pin dislocations. The overall properties of the Cu-Fe alloys were excellent. The synergistic addition of Mg and Si significantly improved the mechanical properties of the alloys, but the electrical conductivity slightly declined.

Study on the Microstructure, Mechanical Properties, and Corrosion Behavior of 900 °C-Annealed CoCrFeMnNiSix (X = 0, 0.3, 0.6, 0.9) High-Entropy Alloys.

In this study, a series of CoCrFeMnNiSix (x = 0, 0.3, 0.6, 0.9) high-entropy alloys (HEAs) were prepared by suspension melting of cold crucible, annealed at 1000 °C, and then quenched at 900 °C. The changes in the microstructure of the HEAs after the addition of Si were analyzed using X-ray diffraction (XRD), metallographic microscope, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). The hardness, room-temperature friction, and wear behavior, room-temperature compressive properties, and corrosion resistance of the annealed CoCrFeMnNiSix HEAs were also studied. The results show that when the Si content is 0 and 0.3, the annealed CoCrFeMnNiSix HEA exhibits a single face-centered cubic (FCC) structure. As the silicon content increases, a face-centered orthorhombic (FCO) phase appears. At a Si content of 0.9, a hexagonal close-packed (HCP) phase is observed. After heat treatment, the hardness of the CoCrFeMnNiSix HEAs increases continuously with the addition of Si. The HEA with a Si content of 0.9 achieves the highest hardness of 974.8 ± 30.2 HV. The HEA with a Si content of 0.6 reaches the highest compressive strength and yield strength, which are 1990.3 MPa and 1327.5 MPa. When the Si content is 0.9, the HEA shows the smoothest surface after wear, with the best wear resistance, achieving a value of 0.21 mm-1. In the CoCrFeMnNiSix HEAs after 900 °C heat treatment, the HEA with a Si content of 0.6 exhibits the lowest self-corrosion current density of 0.23 µA/cm2 and the highest pitting potential of 157.65 mV, indicating the best corrosion resistance.

Effect of Si additions on the microstructure and properties of Cu-Cr-Mg alloy

Trace Si additions contribute to improve the mechanical properties of Cu-Cr-Mg alloys. The effect of different Si contents (0, 0.06, and 0.16 wt%) on the microstructure, mechanical, and electrical properties of Cu-0.3Cr-0.2 Mg (wt.%) alloys was studied experimentally. It is found that the peak-aged with 0.06 wt% Si alloy exhibits the highest hardness and strength, mainly due to the moderate refinement of FCC-Cr precipitates by Si addition. However, excessive Si addition (0.16Si) results in the formation of Cr3Si phase, which consumes Cr elements, reducing FCC-Cr precipitation and hence degenerates precipitate strengthening. Results further suggest that the electrical conductivity decreases with increasing Si content due to the increased electron scattering. Thermodynamic calculation reveals that the nucleation driving force of Cr3Si is an order of magnitude smaller than the transformation energy from FCC-Cr to BCC-Cr, suggesting the nucleation of Cr3Si probably precedes the transformation of FCC-Cr to BCC-Cr and thereby facilitates the stabilization of FCC-Cr precipitates. This work provides an insight on understanding microstructural/property evolution of Cu-Cr-Mg-Si alloy and designing high-strength Cu-Cr-Mg alloys through Si addition.

Rapid fabrication and corrosion behavior of 3D-porous Cu-Al-Si compounds via low-energy self-exothermic reaction

In this study, porous Cu-Al-Si intermetallic compounds with three-dimensional structures were rapidly prepared by a novel self-exothermic reaction. By this method, Si was successfully solid-solved into CuAl intermetallic compounds and achieved better fusion with them. The effects of Si addition on their oxidation resistance and corrosion resistance were compared. The findings indicate that the minimum weight gain of the Cu-Al-Si product is only 1.48 % after oxidation at 800 °C for 288 h. Si facilitates the creation of a continuous Al2O3 protective layer on the surface of the porous Cu-Al-Si intermetallics skeleton, thereby preserving its internal structure while significantly enhancing its oxidation resistance. The incorporation of Si to Cu-Al intermetallics enhances the stability of the passivation film on the material's surface, increases the resistance of the passivation film, and effectively restricts the electrochemical reaction between the material and the corrosive medium.

Effect of metalloid element on the microstructural and mechanical properties of AlCoCrCuFeNi high-entropy alloys

ABSTRACT The impact of the metalloid element silicon (Si) addition on the microstructural and mechanical properties of the AlCoCuCrFeNiSix high-entropy alloy system is examined in this paper. The alloys were synthesized using a vacuum arc melting route. X-ray diffraction was used to analyse the current high-entropy alloys’ phase formation to comprehend the alloying process’s behaviour. It is evident from the peak pattern of the X-ray diffraction that the inclusion of Si promotes the growth of body-centred cubic structures. The microhardness and wear resistance were increased by increasing the Si content from 0 to 0.9. Si presence enhances the hardness of the alloys and strengthens the grain boundary. Improved hardness and wear resistance results from the enhanced body-centred cubic-phase formation, which poses a barrier to the dislocation movement and prevents further deformation. Furthermore, the inclusion of Si improved corrosion resistance in potentiodynamic polarization measurements. Excellent compressive strength is possessed by all of the high-entropy alloys with Si addition.

Influence of Si Content on the Microstructure, Wear Resistance, and Corrosion Resistance of FeCoNiCrAl0.7Cu0.3Six High Entropy Alloy

This study explores microstructure, wear, and corrosion resistance properties of FeCoNiCrAl0.7Cu0.3Six (x = 0, 0.2, 0.3, 0.5) high-entropy alloys. The FeCoNiCrAl0.7Cu0.3Six alloy contains FCC and BCC structures; as the x increases, the FeCoNiCrAl0.7Cu0.3Si0.2, FeCoNiCrAl0.7Cu0.3Si0.4, and FeCoNiCrAl0.7Cu0.3Si0.5 high-entropy alloys transition to BCC structures. The morphological transition in FeCoNiCrAl0.7Cu0.3Six evolves from bamboo leaf-like intergranular features to a discontinuous intergranular structure as Si content increases. The hardness of these alloys gradually increases with higher Si content. The addition of Si promotes a uniform distribution of Cr within and between grains, reducing the intergranular segregation of Cu. Al and Ni show a consistent pattern of elemental distribution throughout the alloy. Wear measurements of FeCoNiCrAl0.7Cu0.3Six alloys demonstrate that adding Si enhances wear resistance, resulting in smoother wear surfaces with reduced deformation. The wear mechanism for all alloys is primarily abrasive, with no brittle fractures observed. Corrosion resistance is optimized when Si content is 0.2, with pitting corrosion being the primary corrosion form.

Enhancing high-temperature chloride molten salts corrosion resistance of 310S steel with Si-added Ni–Al coating

Ni–Al based coating is one of the common high temperature and corrosion resistant protective coatings. In the present paper, the effect of Si content on the formation of Al2O3 layer and the corrosion resistance of Ni–Al coating to chloride molten salt was studied. The research results show that the Ni–Al coatings with varying Si content mainly form NiAl2O4 and Al2O3 oxide layers after pre-oxidation, and form a three-layer structure after molten salt corrosion. The appropriate amount of Si added to the Ni–Al coating can promote the formation of the α-Al2O3 layer during pre-oxidation and thermal corrosion, improving the corrosion resistance of the coating to high temperature chloride molten salt, and hindering the diffusion of Cr elements. Particularly, the Ni–Al coating with Si content of 1.2 at.% has the thickest and densest Al2O3 protective layer, showing the best corrosion resistance. The simulation results shows that compared with the Ni–Al coating without Si, the Cl atoms in the Si-added Ni–Al coating need to overcome greater energy barriers to diffusion during the molten salt corrosion process, which also indicates that the addition of Si can improve the corrosion resistance of the coating.

Microstructure evolution and degradation process of AlCrTiSiN coatings with different Si contents at high temperatures

The microstructure evolution of AlCrTiN and AlCrTiSiN coatings containing 4, 6.8, and 10.6 at.% Si was studied at temperatures ranging from 800 to 1100 °C. The AlCrTiN coating exhibits a single-phase fcc-(Al,Cr,Ti)N structure, while the AlCrTiSiN coatings transition from a nanocomposite structure, composed of fcc-(Al,Cr,Ti)N and amorphous a-SixNy, to a fully amorphous structure as the Si content increases. The hardness and adhesion strength of coatings initially rise, peaking at 24 GPa and 44 N respectively, due to the formation of the nanocomposite structure. However, these properties decline as the coatings become fully amorphous. At elevated temperatures, severe oxidation leads to the gradual formation of layered oxides. Concurrently, phase transformation, spinodal decomposition, and crystallization occur within the nitride layer. The addition of Si enhances oxidation resistance by promoting the rapid formation of a dense and protective oxide layer, and by reducing nitrogen release and TiO2 formation. However, at 1000 and 1100 °C, the coating with 10 at.% Si exhibits slightly faster oxidation compared to the 6.8 at.% Si coating, as the increased Si content reduces the Al content, limiting the coating's ability to regenerate the protective oxide layer.

Atomic mechanism of enhanced thermal stability in Al-Cu-Mg-Si alloys with a low Cu/Mg ratio

The Si-modified Guinier-Preston-Bagaryatsky (GPB) zones are claimed to be responsible for the high-thermal stability of Al-Cu-Mg-Si alloys with a low Cu/Mg ratio. However, the structure of this phase and its formation mechanism remain unclear. In the present study, the precipitation behaviors of two Al-Cu-Mg alloys with or without Si addition upon thermal aging at 200 °C are characterized using atomic-resolution imaging techniques and the ab initio calculation. It is found that the Si-modified GPB zone is needle-shaped β'/GPB composite with core/shell structure. The core part is β' phase (Mg9Si5), while the shell is composed of the conventional GPB zones. In the early stage of aging, β' phase precipitates rapidly and acts as the heterogeneous nucleus of GPB zones. With the aging time extending to 60 h, the diameter of the β'/GPB composites remains almost constant, since the GPB zones effectively hinder the coarsening of the internal β' phase, thus promoting the thermal stability of the alloy as compared with the Si-free alloy. Our results clarify the mechanism of Si, at atomic scale, to improve the thermal stability of Al-Cu-Mg alloys with a low Cu/Mg ratio.

Thermodynamic prediction and experimental verification of phase transformation kinetics in 3Mn steel with Ti and V microadditions

AbstractIn this work, the phase transformation kinetics and precipitation processes were studied using thermodynamic calculations and a dilatometric method to determine the optimal chemical composition of medium-Mn steel and its initial parameters of heat treatment. The investigated steel is intended for forgings with the microstructure composed of bainitic matrix and retained austenite (RA). An influence of Al and Si on the Ms temperature was characterized to obtain the best chemical composition in terms of RA stabilization. Theoretical continuous cooling transformation (CCT) and time–temperature transformation (TTT) diagrams were determined and compared with dilatometric results. Microstructural observations were compared with the dilatometric results. The hardenability of steel was high due to increased Mn and Mo additions. A very small fraction of cementite is expected in the microstructure due to Al and Si additions. The shortest time to start and finish the bainitic transformation was noted for the isothermal heat treatment at 420 °C. The completion of the bainitic transformation took about 25 min and is acceptable from the industrial point of view. The obtained results constitute a good basis for designing thermomechanical processing routes of bainitic steels with RA.

Effects of solute alloying elements on solid solubility of TiC in austenite

Solute elements in microalloying steel affect the solid solubility of microalloying elements, and thus affect the second phase precipitation in steels. In this work, the influences of solid solution elements, especially Si and Al, on the solubility product of TiC in austenite were studied using the two-sublattice model. The results show that both Al and Si additions reduced the solubility product of TiC in the austenite region, and the reduction degree of TiC solubility product with Al addition was increased with increasing temperature, while it was decreased with Si addition. In addition, Mn, Mo and Cr additions all increased the solubility product of TiC in the austenite region, and the increment degree of TiC solubility product with Mo addition was decreased with increasing temperature, while it changed slightly with Mn or Cr addition with temperature. The model of solubility product of TiC without alloying additions in austenite was modified, and the calculating result was highly consistent with findings of literatures. Finally, a calculation model of TiC solubility product considering the influence of alloying elements was established.

Ab initio molecular dynamics investigation on hydrogen diffusion behavior in liquid aluminum alloy melts

In this work, ab initio molecular dynamics (AIMD) simulations under both NVT and NPT ensembles were performed to study the influence of alloying elements of Mg, Fe, Si, Ti, Cu, Zn, F, and Cl on the H diffusion behavior in liquid aluminum melt. It is found that the diffusion coefficient of H simulated by AIMD under the NVT model is highly consistent with the reported experimental results. Specifically, the addition of Cu, Cl, Si, and Zn is inclined to increase the diffusion coefficient of H in the melt, whereas the opposite result is observed with the addition of F, Fe, and Ti. Moreover, it is proved that the H diffusion coefficients are positively correlated with the H-Al bond lengths and the coordination number of H in a constant volume system. The obtained results deepen the understanding of the diffusion of H atoms in Al melts and contribute to the optimization of existing melt purification technologies.

Evaluation of critical temperatures of as-cast Co-based superalloys as a function of alloying elements and their effect on microstructure

Co-based superalloys are of great interest in the aeronautical and aerospace industry due to their superior thermal performance compared to Ni-based superalloys. This work explores the influence of elemental additions (Ni, Al, Cr, Si, and Ti) on the critical temperatures (liquidus, solidus, solvus, and eutectic) and microstructural features of several Co systems fabricated by vacuum induction melting until the final Co-30Ni-10Al-4Cr-2Si-2Ti (wt%) composition was obtained. Differential Scanning Calorimetry results indicated high thermal stability concerning the γ' phase formation. Si and Ti additions suppressed the eutectic presence in the proposed superalloy, which is desirable to avoid the incipient melting of components. Instead, the present work exhibits a low-density Co-based superalloy conformed of a continuous γ/β microstructure with γ' precipitating uniformly. These characteristics make the Co-30Ni-10Al-4Cr-2Si and Co-30Ni-10Al-4Cr-2Si-2Ti superalloys promising candidates to be subjected to high temperatures in comparison with current Co-based superalloys.

Additively manufactured FeCoNiSi0.2 alloy with excellent soft magnetic and mechanical properties through texture engineering

High-entropy alloys are widely used as structural materials and hold potential as functional materials. This study aims to develop a soft magnetic medium entropy alloy FeCoNiSi0.2 (Si0.2 MEA) with excellent soft magnetic properties and higher ductility using additive manufacturing technology. The microstructure of Si0.2 MEA is characterized by texture and large grains, with a single FCC phase structure. The texture strength of MEA initially increases and then decreases with the addition of Si, with Si0.1 MEA exhibiting the strongest fiber texture. Among the four FeCoNiSix MEAs, Si0.2 MEA demonstrates the best tensile properties (i.e. δ ∼39 %, σ0.2–287 MPA, σb∼551 MPa). The correlation generalized stacking fault energy calculation model indicates that Si0.2 MEA has the lowest generalized stacking fault energy (∼7 mJ/m2), suggesting superior ductility. The synergistic effect of texture and large grains promotes the formation of a magnetization “easy axis”, which makes Si0.2 MEA exhibit the best soft magnetic properties (Ms:150emu/g, Hc:1.04Oe). These results provide a new paradigm for developing laser additively manufactured soft magnetic medium entropy alloy.