Face-centered Crystal Lattice Research Articles

ATOMISTIC AND CONTINUAL DETERMINATION OF STRESS FIELDS AT A CRACK TIP IN ANISOTROPIC ENVIRONMENT WITH CUBIC SYSTEM

The article presents a comparative analysis of stresses associated with a crack tip in an anisotropic medium with cubic symmetry of elastic properties under mixed mode loading conditions, using two different approaches: atomistic and continuum approaches. The atomistic approach is based on the use of the molecular dynamics method implemented in the open source Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The continuum approach is based on the classical theory of elasticity of anisotropic media, in which the mechanical fields associated with the crack tip are represented using series that generalize the well-known representation of M. Williams to the case of anisotropic media. Using the method of molecular dynamics, a large series of calculations of loading of single-crystal copper and aluminum plates with a face-centered crystal lattice, weakened by a central crack, was carried out using the embedded atom potential (EAM). Molecular dynamics modeling is aimed at determining atomistic stresses and strains near the crack tip. The calculated atomistic stresses were compared with the stress field determined by the continuum theory of elasticity of anisotropic media for crystal lattices with cubic symmetry of elastic properties. A comparative analysis was carried out for the angular dependences of the stress and strain tensor components at different distances from the crack tip for the entire range of mixed strain modes: from perfect normal tension to loadings close to perfect transverse shear. It is established that the fields found on the basis of two fundamentally different approaches (discrete and continuum) are fully consistent with each other. It is demonstrated that the mathematical methods of continuum fracture mechanics can be used to describe stress, strain, and displacement fields at the atomistic level.

ОСОБЕННОСТИ СТРУКТУРООБРАЗОВАНИЯ ПЕРЕХОДНОЙ ЗОНЫ В СЛОИСТОМ КОМПОЗИЦИОННОМ МАТЕРИАЛЕ, ПОЛУЧЕННОМ СВАРКОЙ ВЗРЫВОМ

The paper presents the research on special aspects of structure formation in the transition zones of a layer metal material made of structural carbon and alloy stainless steels with an internal protector. The authors specify the order of layers arrangement. As an industrial method of producing such a material, the explosion welding technology was selected, which ensures the production of three-, four- and six-layer materials with one and two internal protectors per one explosion. The selection of optimal process parameters was carried out using computer modeling in the LS-DYNA software product. By calculation, the authors determined the main technological parameters of the process, which provide in the contact zone at each interlayer boundary the ratio of the amplitude of the generated waves to their length in the range from 0.3 to 0.5. Mechanical tests of multilayer workpieces were carried out. The shear strength of layers was from 320 to 410 MPa, the ultimate tensile strength of the main layer was from 520 to 710 MPa, the impact resistance was from 290 to 740 kJ/m2, and the bending angle under static loading was 140 degrees and higher. The authors determined the phase composition and characteristics of the crystallographic structure of transition zones of a layer metal material with an internal protector. The study identified the presence of γ-Fe with a face-centered crystal lattice, two cubic structures, one hexagonal, and one orthorhombic. On the samples with artificial pitting, the authors determined their influence on the rate of anodic dissolution of a protective layer when contacting with an aggressive environment. The study shows that the interlayer boundaries with a homogeneous structure and minimal thickness have the highest corrosion resistance.

Квантово-механический подход к описанию взаимодействия СВЧ-электромагнитного излучения с тонкими проводящими пленками

The paper presents a quantum-mechanical analysis approach of the electromagnetic radiation interaction with the ultrathin conducting films in the frequency range of 1–200 GHz. It was shown that at film thicknesses less than 10 nanometers, the structure symmetry of the atomic conductor lattice must be taken into account, a violation of which can lead to the appearance of a band gap, which greatly differs from the crystalline material. The band gap has a strong influence on the conductivity of a thin metal film and on its electromagnetic properties. Using aluminum as an example, it is shown that in case of symmetry breaking of the face-centered crystal lattice, the band composed of the valence and the conduction bands splits with the band gap formation of 0.07 eV.

Mechanical Alloying with the Partial Amorphization of the Fe–Cr–Co–Ni–Mn Multicomponent Powder Mixture and Its Spark Plasma Sintering to Produce a Compact High-Entropy Material

The results of studying the influence of mechanical alloying (MA) on the surface morphology, microstructure, and atomic–crystalline structure of particles of the Fe–Cr–Co–Ni–Mn multicomponent powder mixture are presented. The initial components are as follows: the R-10 radio-engineering carbonyl iron powder with average particle size d = 3.5 μm, the NPE-1 nickel powder with d = 150 μm, the PK-1u cobalt powder with d < 71 μm, the PKh-1M chromium powder with d < 125 μm, and the MR0 manganese powder with d < 400 μm. The MA of the prepared mixture was performed in an AGO-2 water-cooled mechanical activator using 9-mm steel balls with an acceleration of 90 g in air. The alloying time varies from 5 to 90 min. The ratio of the ball weight to the mixture weight is 20 : 1. X-ray diffraction patterns of the initial and alloyed mixtures, as well as of the sample formed by sintering, are recorded using a DRON 3M diffractometer in FeKα radiation at 2θ = 30–100°. The microstructure of the mixture particles and the compact sample metallographic specimen after sintering are investigated by scanning electron microscopy. It is established that the peaks of initial components are absent in the X-ray diffraction pattern after mechanical activation for 90 min, and peaks corresponding to the phase representing the γ-Fe-based solid solution having a face-centered crystal lattice are presented. Herewith, the fraction of the amorphous phase increases to 20%. A compact single-phase material is formed from the mixture prepared after 90-min alloying by spark plasma sintering at 800°C for 10 min. Its density is 7.49 kg/cm3, resistivity is 0.94–0.96 × 10–6 Ω m, and microhardness is 306–328 kg/mm2. The phase is uniformly distributed over the volume.

ПІДВИЩЕННЯ СТРУКТУРНОЇ СТАБІЛЬНОСТІ ТА ВЛАСТИВОСТЕЙ ЖАРОМІЦНИХ НІКЕЛЕВИХ СПЛАВІВ ДЛЯ ЛОПАТОК ГТД ОБРОБКОЮ НАНОМАТЕРІАЛАМИ

An analytical review of existing views on the problem of increasing the heat resistance, heat resistance, and durability of high-temperature nickel alloys of the ZhC3 group of blades of gas turbine engines is carried out. The effect of alloying elements of alloys on structural transformations, types of hardening and corrosion resistance is analyzed. A complex powder modifier based on titanium carbonitride Ti (CN) is proposed for processing nickel melts. The choice of nanodispersed Ti (CN) carbonitride powders of a fraction of less than 100 nm as modifiers of low-alloy steels is substantiated. It has been established that Ti (CN) titanium carbonitride particles have a face-centered crystal lattice. The necessary criteria for the selection of nanopowder modifiers have been obtained: insolubility in the melt, correspondence of crystal lattices with the matrix of steel, proportionality with the critical radius of the austenite embryo during crystallization. A mechanism for the interaction of a steel melt with a layer of a nanodisperse composition is established. The macro- and microstructure of nickel alloys ZhC3, ZhC3DK was investigated. An analysis of microdiffraction patterns of particles is carried out, the nanopowders are shown to belong to solid crystalline bodies with a metallic bond. The coarse-grained and low-plastic matrix of the nickel alloy is under the influence of a large local loading, which contributes to the premature cracking of grain boundaries. Modification leads to significant changes in the structure of the alloy ZhC3 in comparison with the unmodified state. The structure of ZhC3 after modification is homogeneous, fine-grained. In modified samples, the grinding of grain was achieved 3 ... 5 times and the structure was stabilized in comparison with the initial state. Mechanical studies of samples in a modified state showed an increase in all parameters: tensile strength by 10 %; yield strength - by 13 %; the elongation by 20 % and the impact strength by 40 % compared to the original samples. Tests of samples for heat resistance showed a decrease in the depth of corrosion at a temperature of 1000 °C in the modified state on average by 25 %, which confirms the effect of modifying the alloys with nanodispersed modifiers.

MECHANICAL ALLOYING WITH PARTIAL AMORPHIZATION OF FE–CR–CO–NI–MN MULTICOMPONENT POWDER MIXTURE AND ITS SPARK PLASMA SINTERING FOR COMPACT HIGH-ENTROPY MATERIAL PRODUCTION

This paper presents the results of studying the mechanical alloying (MA) effect on the surface morphology, microstructure and atomic-crystal structure of multicomponent Fe–Cr–Co–Ni–Mn powder mixture particles. The following materials were used as initial components: radio-engineering carbonyl iron powder (R-10 with an average particle size d = 3,5 μm), nickel powder (NPE-1, d = 150 μm), cobalt powder (PK-1u, d &lt;71 μm), chromium powder (PH-1М, d &lt;125 μm) and manganese powder (MR0, d &lt;400 μm) were used. MA of the prepared mixture was carried out in the AGO-2 water-cooled mechanical activator using 9 mm steel balls with an acceleration of 90 g in air. Alloying time varied between 5 and 90 minutes. The ratio of ball mass to the mass of the mixture was 20 : 1. X-ray patterns of the initial and alloyed mixtures and the sample obtained by sintering were made on the DRON 3M diffractometer on FeKα radiation in the range of angles 2θ = 30°÷100°. The particle microstructure of the mixtures and compact sample section after sintering was studied by scanning electron microscopy. It is found that no peaks of the initial components are present on the X-ray pattern of the mixture after 90 minutes of mechanical activation, but there are peaks corresponding to the γ-Fe-based solid solution phase having a face-centered crystal lattice with an amorphous phase content increased by 20 %. A compact single-phase material was obtained by spark plasma sintering at 800 °С for 10 minutes from the mixture after 90-minute alloying. Material density was 7,49 kg/cm3, specific electrical resistivity was 0,94÷0,96·10–6 ·m, microhardness was 306÷328 kg/mm2, and the phase was distributed uniformly throughout the volume.

The effect of stacking fault energy on acoustic emission in pure metals with face-centered crystal lattice

The effect of stacking fault energy on acoustic emission in pure metals with face-centered crystal lattice

Investigation of Relationship between Structural and Crystallographic Condition of some Constructional Materials and their Mechanical Properties

This paper presents the results of an analytical study into the relationship between the strength and plastic properties of a series of structural materials. For this purpose the behavior of different materials during the stretching process of flat tensile samples with a circular hub was studied. It was found that the criterion of relative strength A depends on the structure and type of the crystal: materials, having a body-centered crystal lattice A &lt; 1, and materials, having face-centered crystal lattice, A &gt; 1. Astable linear relationship, depending on the structure and the type of crystal lattice of the material, between the criterion of relative strength A, geometric parameters of the sample (R and b) with the hub, length of the zone of material’s plastic flow lp and tension δ was found to exist.

CO2Reforming of CH4over Ru-Substituted Pyrochlore Catalysts: Effects of Temperature and Reactant Feed Ratio

Dry reforming of methane (DRM) was performed on a 1% Ru-substituted lanthanum strontium zirconate pyrochlore, La1.97Sr0.03Ru0.05Zr1.95O7 (LSRuZ), and results were compared to a commercially available 0.5% Ru/Al2O3 catalyst at different bed temperatures and reactant feed ratios. X-ray diffraction of the fresh LSRuZ confirmed the formation of the La2Zr2O7 pyrochlore face-centered crystal lattice using a modified Pechini synthesis procedure. Results from X-ray photoelectron spectroscopy (XPS) on the fresh calcined pyrochlore showed the presence of RuO2, which was also present along with both RuO3 and RuO4 in the 0.5% Ru/Al2O3 catalyst. Temperature-programmed reduction (TPR) showed that Ru was reducible in both catalysts, but the primary TPR peak for Ru reduction was 140 °C higher for the LSRuZ pyrochlore than that for 0.5% Ru/Al2O3, consistent with the incorporation of Ru within the pyrochlore. The effect of the CH4/CO2 feed ratio on the activity was studied by varying the feed ratio as 1:1, 2:1, and 1:2 at ...

SURFACE MODIFICATION OF SEMICONDUCTOR THIN FILM OF TiO&lt;sub&gt;2&lt;/sub&gt; ON GRAPHITE SUBSTRATE BY Cu-ELECTRODEPOSITION

Surface modification of graphite/TiO2 has been done by mean of Cu electrodeposition. This research aims to study the effect of Cu electrodeposition on photocatalytic enhancing of TiO2. Electrodeposition has been done using CuSO4 0,4 M as the electrolyte at controlled current. The XRD pattern of modified TiO2 thin film on graphite substrate exhibited new peaks at 2θ= 43-44o and 2θ= 50-51o that have been identified as Cu with crystal cubic system, face-centered crystal lattice and crystallite size of 26-30 nm. CTABr still remains in the material as impurities. Meanwhile, based on morphological analysis, Cu particles are dissipated in the pore of thin film. Graphite/TiO2/Cu has higher photoconversion efficiency than graphite/TiO2. Keywords: semiconductor, graphite/TiO2, Cu electrodeposition

Measure of the closeness of crystal lattices

A numerical measure of the difference between crystal lattices is determined. The fruitfulness of the definition is demonstrated for a specific example concerning the prominence of an orientational correspondence between the body-centered crystal lattice [bcc(bct)] of α-martensite and the face-centered crystal lattice (fcc) of γ-austenite in cases where the latter is perfect and where it differs from a perfect lattice near a screw dislocation.