Si Solid Solutions Research Articles

Silicon-Doped Nanostructured Fe<sub>80</sub>Ni<sub>20</sub> Alloys: The Role of Si on the Microstructure, Morphology and Magnetic Properties

Fe(Ni, Si) solid solutions were elaborated by high energy mechanical alloying from elemental Fe, Ni and Si powdersfor a milling time of 72 h. From X-ray diffraction (XRD) analysis, it has been shown that the Fe(Ni, Si) samples present a single phase in the whole range of Si content and exhibit a solid solution of disordered bcc α-Fe. The lattice parameter a (Å) of the new structures and the mean crystallitessize <D> (nm) were found to decrease with increasing Si contents. In contrast, the microstrain behaviour presents two different stages as the Si contents are increased. Scanning Electron Microscopy (SEM) images confirmed the behaviour of the mean crystallites size, where it can be seen that the addition of Si promotes the reduction of the size of powder particles. The saturation magnetization Ms was found to decrease by a factor of almost 1.4 and the coercively was found to increase by a factor of almost 2.4, when the Si content was increased from x= 0 % to x= 20 %. The Mössbauer spectroscopy confirmed the local in site crystal locations of Si and Ni as they diffuse into the matrix of the bcc α-Fe structure to form a solid solution.

Исследование фононной теплопроводности твердых растворов CoSi-CoGe с использованием ab initio динамики решетки

Lattice thermal conductivity of solid solutions based on cobalt monosilicide and monogermanide was studied. Electrical and thermal conductivities of CoSi and solid solutions of CoGe(x)Si(1-x) (x=0.03 and 0.07) were experimentally measured in the temperature range of 80-350K. Phonon spectra and thermal conductivity in CoGe(x)Si(1-x) solid solutions were calculated using ab initio lattice dynamics. The results of calculations are in good agreement with the results of measurements obtained in the present work and with the literature data. It was shown that already at a content of 10–15 at.% of Ge, the lattice thermal conductivity decreases by about a factor of 2 compared with pure cobalt monosilicide, and at a germanium content of about 70 at.%, the decrease can reach 3.5 times.

Effect of laser claddings of Fe-based alloy powder with different concentrations of WS2 on the mechanical and tribological properties of railway wheel

Laser cladding could be applied on railway wheels to improve their service lives. Fe-based alloy powder is widely used as the laser cladding material due to its good self-fluxing ability and low price. However, the friction coefficients and wear rates of Fe-based alloy laser claddings are high. WS2 is used as the additive for common laser cladding treatment, while it has not been used for claddings on railway wheels. Understanding the influence of WS2 concentration on the mechanical and tribological properties of Fe-based alloy laser claddings on railway wheels has significance for extending the application of laser treatment on railway transit. Therefore, laser claddings of Fe-based alloy powders with different contents of WS2 powder (0, 2%, 4%, 6%, 8%) were produced on the railway CL60 wheel material. Rolling-sliding tests were conducted on a twin-disc tribometer using the uncladded and cladded wheel samples against an uncladded U71Mn rail sample. The results indicated that the microstructure of laser claddings was composed of dendritic and eutectic phases. With the increase in the WS2 content from 0 to 6%, the size of dendritic phases was decreased from around 20 μm to less than 10 μm. With 8% WS2, the size of dendritic phases was increased to around 10–20 μm. Laser claddings of Fe-based alloy powders with WS2 included (Fe, Ni) and (Fe, Si) solid solutions, hard carbide (Cr7C3), Ni–Cr–Fe, and CrS phases. The hardness was increased to 730–820 HV0.5 and residual stresses were changed to be compressive state. Rolling contact fatigue (RCF) cracks preferentially initiated and developed along the boundary between dendritic and eutectic phases. The smallest wear rate and shortest RCF cracks occurred on the cladding from powders with 6% WS2. Thus, the optimum content of WS2 in the Fe-based alloy powder was 6% for laser cladding on the railway wheel material.

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature.

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500-1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge-Si solid solutions (P63 /mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Si solid solution family, and is of interest for optoelectronic applications.

Formation of Fe5Si3 precipitate in the Fe2Al5 intermetallic layer of the Al/steel dissimilar arc welding joint: A transmission electron microscopy (TEM) study

The further strengthening of the Al/steel dissimilar joint is significantly meaningful for car lightweight development in automotive industry. It has been experimentally proved that the use of Si containing aluminum alloy filler material such as ER4043 grade welding wire can effectively improve the joint strength by reducing the FeAl intermetallic interface thickness. However, the specific functioning mechanism of Si has not been clarified explicitly thus controversy still exists. In the present research, an Al/steel dissimilar joint is generated using the variable polarity cold metal transfer (VP-CMT) technique. To address the suppression function of Si on the FeAl intermetallic interface growth clearly, the focused ion beam (FIB) is conducted to extract the testing sample right at the interface, which is subsequently investigated under TEM. According to the obtained results, the intermetallics formed at the FeAl interface are generally Fe4Al13 phase on the aluminum side and Fe2Al5 phase adjacent to the steel side. Also, rod-shaped Fe5Si3 precipitates are confirmed in the Fe2Al5 matrix near the steel side, rather than Si solid solutions or ternary Fe-Al-Si phases stated in the previous researches. As indicated by the dislocation distribution in the Fe2Al5 matrix, the generation of Fe5Si3 precipitates considerably suppresses the brittle Fe2Al5 fracture. Such phenomenon clarifies the Si element functioning mechanism of improving the Al/steel dissimilar joint quality.

Three-Component Zone-Melting Method: Modeling of the Concentration-Component Distribution in Single Crystals of Ge–Si Solid Solutions

The concept and theoretical basis of the three-component zone melting method is given for growing single crystals of semiconductor solid solutions using seeds from constituent components. In the Pfann approximation, the problem of the axial concentration distribution of components in Ge–Si single crystals grown at different values of the operating parameters such as the length of the melted zone and the composition of the initial macrohomogeneous rods of solid solutions is solved. Analysis of the obtained results determines the potentialities of the method and the optimal conditions for growing single crystals with given homogeneous and graded compositions in the entire continuous series of Ge–Si solid solutions. It is shown that the three-component zone-melting method is promising for the growth of single crystals of semiconductor solid solutions.

Fabrication of Cu–Ni–Si alloy by melt spinning and its mechanical and electrical properties

Cu alloys with compositions of Cu-3.2Ni-0.7Si (wt. %) and Cu-2.8Ni-0.7Si (wt. %) were prepared by melt spinning. Effects of composition, spinning rate, aging temperature and time on microstructure, precipitation of reinforcing phases, mechanical and electrical properties of Cu–Ni–Si alloys were investigated. Melt spinning could produce continuous Cu alloy ribbons with thickness and width of the ribbons mainly dependent on the cooling rate. Columnar grains of super-saturated Cu–Ni–Si solid solutions grew in the ribbons. The melt-spun Cu–Ni–Si alloys had a faster aging kinetics in comparison with commercial alloys of similar compositions. Peak-aging of the melt spun alloys appeared after heating at 400 to 550 °C for 1 to 2 h to show maximum tensile strength of 650 to 700 MPa. Prolonged heating resulted in large precipitates on the grain boundaries and formation of precipitation-free zones around each grain with sharp drop of tensile strength. Precipitation of nano δ-Ni2Si rather than other phases was the main reason for the enhanced mechanical properties at peak-aging. The peak- and slightly over-aged ribbons had a good electric conductivity up to 55% IACS.

Microstructural Evolution and Mechanical Behavior of Lead-Free Silicon Brass Manufactured by Low-Pressure Die Casting

Low-pressure die casting (LPDC) has been widely used to process aluminum and magnesium alloys; however, it has yet to be applied to manufacture brass alloys. This study investigates the microstructural evolution and mechanical behavior of a lead-free CuZnSiAl silicon brass via a variable-controlling approach on the basis of a faucet casting by LPDC. The manufactured silicon brass castings are predominantly composed of bcc β-CuZn(Si, Al) and minor fcc α-Cu(Zn, Si) solid solutions. The silicon brass castings also predominantly exhibit short rod-like or granular α phases, which distinctly differ from the acicular α morphology obtained by conventional gravity casting. The manufactured silicon brass castings which contain finer β grains and short rod-like or granular α phase exhibit superior mechanical properties. Their optimal mechanical properties—elongation of 15.0%, yield strength of 359.8 MPa, and ultimate tensile strength of 598.9 MPa—are far superior to those of the typical lead brass HPb59-1. The results obtained in this study provide insight into the manufacture and design of lead-free silicon brass castings by LDPC.

Effect of the Addition of Silicon on the Properties of Germanium Single Crystals for IR Optics

Homogeneous Sb-doped single crystals of Ge–Si solid solutions are grown with a silicon content of 0.2 to 0.8 at %. The optical absorption of single crystals with a resistivity of (2–3) Ω cm is studied by IR Fourier spectroscopy at a wavelength of 10.6 μm in the temperature range from 25 to 60°C. It is found that the introduction of silicon into antimony-doped germanium improves the temperature stability of the optical properties of the crystals.

Влияние добавок кремния на свойства монокристаллов германия для инфракрасной оптики

AbstractHomogeneous Sb-doped single crystals of Ge–Si solid solutions are grown with a silicon content of 0.2 to 0.8 at %. The optical absorption of single crystals with a resistivity of (2–3) Ω cm is studied by IR Fourier spectroscopy at a wavelength of 10.6 μm in the temperature range from 25 to 60°C. It is found that the introduction of silicon into antimony-doped germanium improves the temperature stability of the optical properties of the crystals.

Cyclic tensile response of Mo-27 at% Re and Mo-0.3 at% Si solid solution alloys

Stress-controlled uniaxial cyclic tensile tests were conducted on binary Mo-27at% Re and Mo-0.3at% Si solid solutions as a function of temperature and compared against the previously reported cyclic response of pure Mo. The Mo-27at% Re alloy with a recrystallized grain size of ~30µm was evaluated in the temperature range 25°C–800°C at R=0.1 and stress range that was 80% of the ultimate tensile strength (UTS); a peak in fatigue life was observed between 300°C and 500°C. The decrease in fatigue life at the higher temperatures of 700°C and 800°C is attributed to dynamic strain aging. Transmission electron microscopy of the cyclically-deformed alloy revealed parallel bands of dislocation at room temperature that transitioned to a uniform cell structure at 500°C and back to orthogonal planar arrays at 800°C. The as-extruded Mo-0.3at% Si alloy was evaluated from 25°C to 1200°C and showed superior fatigue life and ratcheting strain resistance as compared to pure Mo and the Mo-27at% Re alloy (within the temperature range where data were available for comparison). The superior resistance is attributed to the high density of dislocations within the material in this mostly unrecrystallized state rather than Si in solid solution. Above 800°C, the ratcheting strain increases and fatigue life decreases rapidly with increasing temperature and is associated with dynamic recovery.

Modeling the concentration profiles of aluminum and indium impurities in crystals of germanium–silicon solid solutions

A one-dimensional problem of the axial distribution of Al and In impurities in uniform crystals of Ge–Si solid solutions grown by double feeding of the melt method has been solved in the Pfann approximation. The mathematical modeling results suggest that the impurity concentration profile in Ge–Si crystals of constant composition can be varied in a wide range through appropriate changes in the relationship between the crystal growth rate and the rates of feeding the melt using germanium and silicon rods. We demonstrate the possibility of growing completely homogeneous Ge–Si kAl,Inl crystals, in terms of both the concentrations of their major components and the impurity concentration profile.

Estimation of intrinsic diffusion coefficients in a pseudo-binary diffusion couple

Major drawback of studying diffusion in multi-component systems is the lack of suitable techniques to estimate the diffusion parameters. In this study, a generalized treatment to determine the intrinsic diffusion coefficients in multi-component systems is developed utilizing the concept of a pseudo-binary approach. This is explained with the help of experimentally developed diffusion profiles in the Cu(Sn, Ga) and Cu(Sn, Si) solid solutions.

Anomalous spin relaxation and quantum criticality in Mn1 − x Fe x Si solid solutions

We report results of the high frequency (60 GHz) electron spin resonance (ESR) study of the quantum critical metallic system Mn1 − xFexSi. The ESR is observed for the first time in the concentration range 0 < x < 0.24 at temperatures up to 50 K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of Wolfle and Abrahams, are observed at quantum critical points x* ∼ 0.11 and xc ∼ 0.24.

Quantum bicriticality in Mn1 − x Fe x Si solid solutions: Exchange and percolation effects

The T-x magnetic phase diagram of Mn1 − x Fe x Si solid solutions is probed by magnetic susceptibility, magnetization and resistivity measurements. The boundary limiting phase with short-range magnetic order (analogue of the chiral liquid) is defined experimentally and described analytically within simple model accounting both classical and quantum magnetic fluctuations together with effects of disorder. It is shown that Mn1 − x Fe x Si system undergoes a sequence of two quantum phase transitions. The first “underlying” quantum critical (QC) point x* ∼ 0.11 corresponds to disappearance of the long-range magnetic order. This quantum phase transition is masked by short-range order phase, however, it manifests itself at finite temperatures by crossover between classical and quantum fluctuations, which is predicted and observed in the paramagnetic phase. The second QC point x c ∼ 0.24 may have topological nature and corresponds to percolation threshold in the magnetic subsystem of Mn1 − x Fe x Si. Above x c the short-range ordered phase is suppressed and magnetic subsystem becomes separated into spin clusters resulting in observation of the disorder-driven QC Griffiths-type phase characterized by an anomalously divergent magnetic susceptibility χ ∼ 1/T ξ with the exponents ξ ∼ 0.5–0.6.

Role of different factors affecting interdiffusion in Cu(Ga) and Cu(Si) solid solutions

A detailed diffusion study was carried out on Cu(Ga) and Cu(Si) solid solutions in order to assess the role of different factors in the behaviour of the diffusing components. The faster diffusing species in the two systems, interdiffusion, intrinsic and impurity diffusion coefficients, are determined to facilitate the discussion. It was found that Cu was more mobile in the Cu–Si system, whereas Ga was the faster diffusing species in the Cu–Ga system. In both systems, the interdiffusion coefficients increased with increasing amount of solute (e.g. Si or Ga) in the matrix (Cu). Impurity diffusion coefficients for Si and Ga in Cu, found out by extrapolating interdiffusion coefficient data to zero composition of the solute, were both higher than the Cu tracer diffusion coefficient. These observed trends in diffusion behaviour could be rationalized by considering: (i) formation energies and concentration of vacancies, (ii) elastic moduli (indicating bond strengths) of the elements and (iii) the interaction parameters and the related thermodynamic factors. In summary, we have shown here that all the factors introduced in this paper should be considered simultaneously to understand interdiffusion in solid solutions. Otherwise, some of the aspects may look unusual or even impossible to explain.

Correlation between structural parameters and magnetic properties of ball milled nano-crystalline Fe–Co–Si powders

The main aim of this research is to fabricate the nano-crystalline Fe–Co–Si alloy with superior magnetic properties to be used in producing soft magnetic composites. The alloy powders were prepared by using a planetary ball mill. Morphological, structural and magnetic evolutions during milling were analyzed by scanning electron microscopy coupled with Energy-dispersive X-ray microanalyzer, X-ray diffractometer and vibrating sample magnetometer. The results confirm the production of the Fe(Co) and Fe(Co,Si) solid solutions after milling. Increasing the milling time did lead to smaller crystallite sizes and lattice parameters, but larger amounts of micro-strain and dislocation density. The magnetic measurements indicate that higher amounts of Si lead to lower values of saturation magnetization. The variations of coercivity could be attributed to the introduction of dislocations and reduction of crystallite size as a function of milling time.

The tensile response of Mo, Mo–Re and Mo–Si solid solutions

Recrystallized, commercially pure Mo, binary Mo–27at.% Re, and as-extruded and variously annealed Mo–0.3at.% Si alloys were tested in uniaxial tension as a function of temperature in vacuum. The Mo–Re solid solution is significantly stronger than Mo and retains the strength to at least 800°C. The alloy exhibits serrated flow in the 500°C–800°C range and this is accompanied by a continuous decrease in ductility with increasing temperature in this temperature range. The recrystallized Mo–0.3at.% Si alloy is softer than pure Mo at room temperature and has high ductility (~60% tensile elongation). In the worked condition, it is significantly stronger (σy>600MPa) but still is ductile at room temperature (~10% tensile elongation). The observation of ductility at room temperature in this Mo–0.3at.% Si solid solution alloy has important implications for multiphase ternary Mo–Si–B alloys of technological interest.

Characterization of nanostructured Fe–Co–Si powder alloy

Abstract The main aim of this research is to fabricate the nano-crystalline Fe–Co–Si alloy to be used in producing soft magnetic composites. The alloy powders were prepared by using a planetary ball mill. Morphological, structural and thermal changes during milling were analyzed by scanning electron microscopy (SEM) coupled with EDX microanalysis, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results confirm the production of the Fe(Co) and Fe(Co, Si) solid solutions after milling. Increasing the milling time has led to smaller crystallite sizes and lattice parameters, but larger amounts of micro-strain in the lattice. Prolonged milling has led to higher lattice parameters due to the segregation of solvent atoms to the grain boundaries.

Atomic pair substitution in BN–C and GaP–Si solid solutions crystals studied by x-ray diffraction

This letter reports about crystal structure, lattice relaxation, synthesis, and phase stability of BN–C and GaP–Si solid solution crystals. The hypothesis of atomic pair substitution is discussed and x-ray diffraction (XRD) proof is provided for the replacement of A IIIB V atomic pairs with C IV pairs. Cubic BN–diamond solid solutions underwent lattice relaxation after phase transformation leading to atomic displacement disorder.