Si Solid Solution Research Articles

Mechanism of Solid-State Amorphization in the Fe-Si-Cu-Mg-O System

Solid-state amorphization process occurring at 600-1060 °C continuous annealing was observed by non-ambient x-ray diffraction on Fe-3%Si-0.5%Cu alloy surface with MgO as thermostable coating. The phenomenon was occurred at α→γ transformation temperatures (920-960 °C) in a layer consisting of Si solid solution in α-Fe and oxides (MgFe)2SiO4, (MgFe)O, SiO2. Amorphous state remained both during heating and cooling to 20 °C. Simulation for diffusion amorphization of Fe (Si) solid solution was proposed. Mg2Si complexes are reduced from oxides by hydrogen then transfer to solid solution and solid-state amorphization is occurred.

Tensile Deformation Behavior of High-Strength Nanostructured Cu–Si Solid-Solution Alloys Processed by Severe Plastic Deformation

Tensile Deformation Behavior of High-Strength Nanostructured Cu–Si Solid-Solution Alloys Processed by Severe Plastic Deformation

Effect of Si content on the uniaxial tensile behavior of Mo-Si solid solution alloys

Recrystallized binary Mo-0.2 wt.% Si (Mo-0.68 at.% Si) and Mo-0.3 wt.% Si (Mo-1.0 at.% Si) alloys and a ternary Mo-0.75 wt.% Si-0.14 wt.% B (Mo-2.5 at.% Si-1.2 at.% B) alloy were tested in uniaxial tension as a function of temperature in vacuum and the results are compared to previous results on recrystallized commercial purity (CP) Mo and a binary Mo-0.1 wt.% Si (Mo-0.34 at.% Si) solid solution alloy. Yield strength increases with increasing Si content at all temperatures examined except at room temperature where the 0.1 wt.% Si alloy demonstrates softening; atomistic simulation confirms this behavior to be associated with Si segregation to the core and the associated ease of kink nucleation. Tensile ductility at room temperature rapidly deteriorates with increasing Si content in solid solution but in the Mo-0.3 wt.% Si solid solution alloy, tensile ductility of ~10% was measured at 300°C and thereafter, it increases rapidly at higher temperatures. Serrated flow occurs in the temperature range 600°C~800°C with the serration amplitude increasing with increasing Si content; atomistic simulation illustrates O trapping by Si in solid solution and subsequent de-trapping/release at higher temperatures that can account for the onset temperature delay of serrated flow in these Mo-Si solid solution alloys relative to commercial purity Mo. The serrated flow phenomenon is accompanied by significant work hardening; the presence of dislocation tangles, dipoles and prismatic loops in specimens fractured above ≥ 700°C accounts for the observed work hardening.

Nanocrystallization and phase formation in Fe73:5Nb3Cu1Si15:5B7 amorphous ribbon under laser heating

Abstract Laser-induced local crystallization in Finemet-type alloy was studied using X-ray diffraction, SEM and EDX methods. For investigated conditions of irradiation (wavelength λ = 1.06 μm, laser power density 50 W/cm2), it was found that primary crystallization starts with the formation of the nanocrystalline α-Fe(Si) solid solution at shorter exposure time and the second step crystallization with the nanocrystalline hexagonal H-phase formation occurs in longer exposure time. Changes in the local element concentration were observed at the surface of the irradiated zone and at the ribbon fracture. It was shown that the nonlinear temperature field due to the laser irradiation resulted in changes of the local elements concentration and this feature changed crystallization mechanism of the Finemet-type alloy.

Study of the Microstructure and Phase Composition of Crude Niobium Electron-Beam Remelting Sublimates

crude niobium. The phase composition of sublimates formed during the first remelting of crude niobium is studied by scanning electron microscopy and X-ray microanalysis. Sublimates typically form structures of two types, i.e., dendritic and lamellar that is connected with niobium refining process conditions and the effect of various factors on sublimate crystallization. Niobium electron beam remelting sublimates are inconsistent with respect to both chemical and phase compositions. A layered structure is typical for the porous part of sublimates that are the basis of the material. The microstructure of another type is dendritic, typical for lamellar and rounded particles with a metallic sheen located within pores or dispersed in the layered part of sublimates. Alternation of phases within each layer is noted for a layered structure. The composition of the phases containing niobium is close to NbAl3 and a solid solution based on niobium (more than 90% Nb). Within the zone of phases consisting of aluminum, there are areas accumulating iron and silicon of variable composition that may be attributed to solid solutions based on Al5FeSi and Al3Fe. The structure of the metallized part of the sublimates consists of light rounded dendrites of niobium aluminide NbAl3, between which there is a phase close in composition to Al8Fe2Si. It is noted that single particles of pure niobium metal are found within the structure of the metallized part of sublimates. It is noted that as expected the main phase is NbAl3 intermetallic. Niobium is also present in the form of silicide Nb5Si3. Aluminum is found in sublimates in elemental form, in solid solution with iron and silicon, or in the form of oxide. Impurity elements are distributed between an oxide phase based on α –Al2O3 (Fe, Si, Ni) and Al–Fe–Si (Cr, Mn, Ni) solid solution.

Microstructures and soft magnetic properties of Fe73.5Cu1Nb3–xSi13.5B9Yx (x=0–1.5) alloys

Based on composition of Finemet alloy, structures and soft magnetic properties of Fe73.5Cu1Nb3–xSi13.5B9Yx (x = 0, 0.5, 1.0, 1.5) alloys formed by replacing Nb (niobium) by Y (yttrium) were studied in this paper. The research results show that when x = 0 or 0.5, rapidly solidified as-cast alloy is Fe amorphous single-phase structure, and Y atoms are dispersed in matrix; when x = 1.0 or 1.5, crystalline phase precipitates. Fe73.5Cu1Nb3–xSi13.5B9Yx (x = 0, 0.5, 1.0, 1.5) alloys begin to precipitate α-Fe(Si) solid solution phase after crystallization annealing above 480 °C, when x = 0.5, grain size is 12.6 nm, which shows that Y can replace Nb in small amount and refine grain size. Fe73.5Cu1Nb2.5Si13.5B9Y0.5 alloy has excellent soft magnetic properties: μm value is 813.1 × 103, which is 36% higher than that of Finemet alloy; μi value is 154.6 × 103, close to that of Finemet alloy, and Bs and Hc values are 1.24 T and 0.56 A/m, respectively, better than those of Finemet alloy. In addition, Fe73.5Cu1Nb2.5Si13.5B9Y0.5 alloy has excellent soft magnetic properties at high temperature, μe value only reduces by 8.8% at 1 kHz with ambient temperature increased from 30 to 150 °C, and μe value is 128.02 × 103 in 150 °C, which is 15.74% higher than that of Finemet alloy.

Microstructure Evolution and Mechanical Behavior of Mo–Si–N Films

The molybdenum silicon nitride (Mo–Si–N) films were deposited by a radio frequency (RF) magnetron reactive dual-gun co-sputtering technique with process control on input power and gas ratio. Composition variation, microstructure evolution, and related mechanical and tribological behavior of the Mo–Si–N coatings were investigated. The N2/(Ar + N2) flow ratios were controlled at 10/20 and 5/20 levels with the tuning of input power on the Si target at 0, 100, and 150 W. As the silicon contents increased from 0 to 33.7 at.%, the film microstructure evolved from a crystalline structure with Mo2N and MoN phases to an amorphous feature with the Si3N4 phase. The analysis of selected area electron diffraction patterns in TEM also indicated an amorphous feature of the Mo–Si–N films when Si content reached 20 at.% and beyond. The hardness and Young’s modulus changed from 16.5 to 26.9 and 208 to 273 GPa according to their microstructure features. The highest hardness and modulus were attributed to nanocrystalline Mo2N and MoN with Si solid-solution. The crystalline Mo–Si–N films showed a smooth tribological track and less wear failure was found. In contrast, the wear track with severe failures were observed for Mo–N and amorphous Mo–Si–N coatings due to their lower hardness. The ratios of H/E and H3/E2 were intensively discussed and correlated to the wear behavior of the Mo–Si–N coatings.

Dimensional Change of Selectively Laser-Melted and Gravity-Cast AlSi10Mg Alloy During Heat Treatment

AlSi10Mg alloy, processed by selective laser melting (SLM) in as-built state and gravity casting in solution-treated state, was heat-treated at several temperatures for different durations, and the resulting dimensional changes were investigated. For the cast AlSi10Mg alloy, the linear dimensional change heat-treated at 200 ˚C was approximately 0.10%, which agreed with that calculated by a theoretical model. The linear dimensional change of the SLM AlSi10Mg alloy heat-treated at 150 ˚C was 0.17%. This indicated that, in as-built state, the concentration of supersaturated solid solution Si in α-Al phase was 1.7 wt% on average, and the lattice constant of α-Al phase was 0.4047 nm. SLM AlSi10Mg alloy contained more than 3 cm3/100 g-Al hydrogen and showed a linear dimensional change of more than 0.6% after the heat treatment at 530 ˚C because of porosity expansion. The relative densities of the SLM AlSi10Mg alloy heat-treated at 150 ˚C for 1800 ks and 530 ˚C for 18 ks were 99.89% and 98.12%, respectively.

Formation of Iron Silicides Under Graphene Grown on the Silicon Carbide Surface

The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive intercalation of iron and silicon atoms into the graphene. Experiments are carried out in situ in ultrahigh vacuum. The elemental composition and chemical state of the surface of prepared samples and their atomic structure are determined by low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy using synchrotron radiation. The thickness of deposited iron and silicon layers varies in the range of 0.1–2 nm, and the sample annealing temperature is varied from room temperature to 600°C. We show that intercalation of silicon into the graphene/Fe/SiC system leads to the formation of a layer of Fe–Si solid solution coated with the surface silicide Fe3Si. The films are effectively protected by graphene from exposure to ambient environment, which opens possibilities for their practical application.

Microstructure and tribological properties of titanium matrix composites reinforced with in situ synthesized TiC particles

In this work, we prepared titanium matrix composites (TMCs) reinforced with in-situ polycarbosilane (PCS)-derived TiC particles. The effects of PCS addition on the microstructure, interface, hardness, and tribological properties were studied. The pyrolysis of PCS leads to the formation of in-situ TiC particles and Si solid-solution at a low PCS content (≤3 wt%). The TiC particles with a particle size of 4.8 μm are uniformly distributed in TMCs and have a well-bonded interface with the Ti matrix. The average grain size of α-Ti decreases from 100.5 μm in pure Ti to 16.1 μm in the Ti-3 wt% PCS composite. The presence of in situ synthesized TiC particles contributes to the excellent wear resistance of the Ti/PCS composites, which is ascribed to the increased hardness, superior load transfer capability, and oxidation wear resistance. The Ti-3 wt% PCS composite possesses the hardness of 4.72 GPa, elastic modulus of 169.23 GPa, and a low specific wear rate of 0.84 × 10−12 m3/(N·m) under constant conditions (3 N, 0.03 m/s). These values are all superior to those of Ti-6Al-4V alloy. This work sheds light on the design of high wear-resistant TMCs for industrial applications.

Strong and tough HfC-HfB2 solid-solution composites obtained by reactive sintering with a SiB6 additive

HfC-HfB2 composite ceramics were successfully reactively spark plasma sintered with a unique SiB6 additive. The incorporation of the SiB6 not only promotes the densification of HfC (up to ~99%), but also significantly enhances the toughness from 4.3 ± 0.5 MPa m1/2 to 14.2 ± 1.4 MPa m1/2. The flexural strength of the HfC-HfB2 composite ceramics was simultaneously improved to 529 ± 48 MPa, which is about 1.4 times higher than that of HfC. This improvement is attributed to the dense composite microstructure comprising an in-situ formed HfB2 and a solid solution of Si and O in HfC and HfB2 grains.

Intercalation Synthesis of Cobalt Silicides under Graphene Grown on Silicon Carbide

The process of formation of cobalt silicides near the graphene-silicon carbide interface by intercalation of single-layer graphene grown on the 4H- and 6H-SiC(0001) polytypes with cobalt and silicon is studied. The experiments were carried out in situ in ultrahigh vacuum. The analysis of the samples is performed by high-energy-resolution photoelectron spectroscopy using synchrotron radiation, low-energy electron diffraction, and also Raman spectroscopy, atomic-force and kelvin-probe microscopies. The thicknesses of the deposited cobalt and silicon layers is varied to 2 nm, and the sample temperature, from room temperature to 1000°C. Co and Si atoms deposited on heated samples is found to penetrate under graphene and are localized between the buffer layer and the substrate, which leads to a transformation of the buffer layer into additional graphene layer. It is shown that the result of intercalation of the system with cobalt and silicon is the formation under two-layer graphene of a Co–Si solid solution and silicide CoSi coated by the surface Co3Si phase. It is shown that the thickness and the composition of the formed silicide films can be changed by varying the amount of the intercalated material and the order of their depositions.

Интеркаляционный синтез силицидов кобальта под графеном, выращенным на карбиде кремния

Abstract The process of formation of cobalt silicides near the graphene-silicon carbide interface by intercalation of single-layer graphene grown on the 4 H - and 6 H -SiC(0001) polytypes with cobalt and silicon is studied. The experiments were carried out in situ in ultrahigh vacuum. The analysis of the samples is performed by high-energy-resolution photoelectron spectroscopy using synchrotron radiation, low-energy electron diffraction, and also Raman spectroscopy, atomic-force and kelvin-probe microscopies. The thicknesses of the deposited cobalt and silicon layers is varied to 2 nm, and the sample temperature, from room temperature to 1000°C. Co and Si atoms deposited on heated samples is found to penetrate under graphene and are localized between the buffer layer and the substrate, which leads to a transformation of the buffer layer into additional graphene layer. It is shown that the result of intercalation of the system with cobalt and silicon is the formation under two-layer graphene of a Co–Si solid solution and silicide CoSi coated by the surface Co_3Si phase. It is shown that the thickness and the composition of the formed silicide films can be changed by varying the amount of the intercalated material and the order of their depositions.

Crystallization kinetics and soft magnetic properties of Fe71Si16B9Cu1Nb3 amorphous alloys

Fe71Si16B9Cu1Nb3 amorphous alloy ribbons were prepared with a single roll polar method. X-ray diffraction analysis of the surface samples was completely amorphous. The thermal stability parameters Tx, Tp, and Tend of amorphous ribbons were measured with a synchronous thermal analyzer under high purity argon gas and analyzed for their crystallization behavior. The heating rate was 10 K min−1, 15 K min−1, 20 K min−1, and 30 K min−1. The Tx and Tp of the Fe71Si16B9Cu1Nb3 amorphous alloy increased with an increase in the heating rate, indicating that the crystallization behavior has a kinetic effect. The crystallization activation energy of the amorphous alloy was calculated using the Kissinger and Ozawa equations, respectively. The calculation results of the two methods were consistent. The sample was annealed (761 K, 786 K, 801 K, and 858 K, holding for 300 s) under the protection of high purity argon. The phase transition and microstructure transformation of the amorphous alloy during isothermal crystallization were analyzed by x-ray diffraction. When the alloy was annealed at 801 K, a single α-Fe(Si) solid solution precipitated on the amorphous matrix. Magnetic properties were measured using a vibrating sample magnetometer and observed by transmission electron microscopy. When the alloy was annealed at 786 K and 801 K, the saturation magnetic induction reached 1.22∼1.27 T, coercivity was as low as 5.3∼7.2 A m−1, and the average grain size was about 10∼20 nm.

Tensile Deformation Behavior of High–Strength Nanostructured Cu–Si Solid–Solution Alloys Processed by Severe Plastic Deformation

Tensile Deformation Behavior of High–Strength Nanostructured Cu–Si Solid–Solution Alloys Processed by Severe Plastic Deformation

Structure of the Fe63.5Ni10Cu1Nb3Si13.5B9 Alloy Nanocrystallized in the Presence of Tensile Stresses

The structure of the Fe63.5Ni10Cu1Nb3Si13.5B9 alloy, which is a classic alloy of the FINEMET type with 10 at % Ni substituted for Fe, has been studied after crystallization in the presence of tensile stresses. It has been shown that, upon the crystallization of the alloy (520°C) both in the presence of a tensile load and without it, nanocrystals of an α-(Fe, Ni)Si solid solution and of the Fe3Si phase are formed with an increase in the duration of annealing from 10 min to 1 hour. When the length of the annealing is further increased from 1 to 4 hours, a tetragonal phase Fe3NiSi1.5 appears in the alloy. A relationship between the structural state (phase composition) of the Fe63.5Ni10Cu1Nb3Si13.5B9 alloy and its magnetic properties and the type of the induced magnetic anisotropy has been shown. The growth of the coercive force, which was previously observed in samples of this alloy as the duration of the annealing was increased to 4 hours, is therefore associated with the appearance of a tetragonal phase in the alloy. The transverse magnetic anisotropy, which is induced in the alloy in the process of nanocrystallizing annealing in the presence of a tensile load, is associated with the formation of nanocrystals of the α-(Fe, Ni)Si solid solution and of the Fe3Si phase with a negative magnetostriction.

57Fe Mössbauer and XRD studies on β-FeSi2 prepared by high energy mechanical attrition

The evolution of different phases of Fe–Si binary system on milling elemental Fe and Si powders has been studied by x-ray diffractometry and 57Fe Mössbauer spectroscopy. The milling has been carried out in argon atmosphere at 1000 rpm using the hardened tungsten carbide medium. The sizes of both Fe and Si are found to be less than 50 nm on milling the mixture for 50 min. Metallic α-FeSi2 formation takes place at this stage due to enhanced reactivity caused by reduction in particle size. The semiconducting β-FeSi2 phase along with ε-FeSi and a metastable Fe–Si solid solution are found to be formed on annealing the milled product at 500 °C. A clean semiconducting β-FeSi2 phase forms on milling Fe and Si for 50 min followed by annealing at 800 °C for 2 h.

The Effect of Copper and Manganese on the Amorphization Process in a Thin Fe–Si–Mg–O Film

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The influence of lattice vibrations and electronic free energy on phase stability of titanium silicides and Si solubility in hcp titanium: A DFT study

In this paper, we evaluated the influence of vibrational and electronic free energy on the thermodynamic phase stability of the Ti5Si3, Ti3Si, Ti6Si3, and other silicides in the binary Ti-Si system and the solubility of Si in α-Ti within the density functional theory and harmonic approximation. We showed, that vibrational and electronic free energy thermodynamically stabilize the Ti3Si silicide and destabilize the Ti6Si3 silicide with respect to the Ti5Si3 and α-Ti. According to our calculations, the transition from equilibrium of Si solid solution with the Ti5Si3 silicide to the equilibrium of Si solid solution with the Ti3Si silicide should be at ∼ 900 K. The account of both the vibrational and electronic free energy increase the calculated solubility limit of Si in α-Ti and make it closer to the experimental one.

Influence of Thermal Exposure on the Structure and Phase Composition of Aluminized Layer Obtained by Explosion Welding and Hot-Dipping Process

It is shown that for the formation of Fe2Al5 intermetallic coatings on the steel surface the aluminized layer obtained by explosion welding must be subjected to a double heat treatment (660 °C, 3 h + 640 °C, 3 h). The first heat treatment ensures the necessary size of the diffusion zone, and the second leads to the formation of a main crack at the interface of Fe2Al5 and FeAl3 intermetallides, which allows to separate the unreacted layer of aluminum and form a coating with hardness of 10 GPa. To form Fe2Al5 intermetallic coating on the steel surface, the aluminized layer, which is immersed in the melt, must be heat treated at 800 °C. The alloying of the diffusion zone by Si and Cu with the replacement of aluminum by the AK12M2 alloy leads to a decrease in the thickness of the diffusion zone and the appearance of additional phases of Al7Fe2Si and (Al,Si)5Fe3 in its composition. The duration of the subsequent heat treatment at 800 °C for complete dissolution of the surface layer increases the hardness of the resulting coating on the basis of a solid solution of Si in Fe2Al5 is 7.5-8 GPa.