Physics of the Solid State最新文献

One of the most crucial tasks for the mining, ore, and wood processing industries is import substitution and reengineering of components from foreign machinery. In this study, the chemical composition and structure of a worn component from crushing equipment are investigated using reengineering principles. It is determined that the examined samples are made from high-chromium cast iron ChKh28, additionally alloyed with molybdenum, vanadium, and nickel. The closest foreign analogue of this material may be the steel grade DIN 1695-81: G-260Cr27. The research results indicate that the casting material underwent heating to temperatures of 950–1050°C, followed by holding at these temperatures for a minimum of 2 h with subsequent air cooling to temperatures of 160–200°C and tempering at 200°C for a minimum of 2 h. This is confirmed by the hardness of the specimens reaching 63–64 HRC and the high degree of equilibrium in their structural-phase state and phase homogeneity.

The effect of a magnetic field on the deformation characteristics of a diamagnetic material Grade C2 lead (99.98% purity) is studied. Initially, the creep process and the microhardness were studied in the initial state, then such studies were carried out using d.c. magnetic fields with inductions 0.3, 0.4, and 0.5 T in the process of creep of the samples and magnetic processing of the samples to study the dynamics of the microhardness and the plasticity parameter. The results of creep tests indicate the presence of an ambiguous nature of the influence of the magnetic field on the creep rate; a change in the sign of the effect was found with an increase in the value of the magnetic field induction to 0.4 and 0.5 T. Also, the alternating nature of the influence of the magnetic field was also established in the study of the microhardness. In addition, it is found that the use of a magnetic field in the process of sample creep quantitatively influences the percentage of the relative residual elongation of the sample (it decreases as compared to the initial one with an increase in the magnetic field induction) upon destruction and the creep process time (increases compared to the initial one at increase in the magnetic field induction). A rational exposure time in a magnetic field during the microhardness tests was revealed, it was found that the maximum effect of a magnetic field manifests itself at exposures for 1 h, in connection with which two exposure modes in this range (0.25 and 0.5 h) are studied.

The study in this work focuses on the properties and structure of the material in the heat-affected zone that occurs during laser metal cutting, depending on the positioning of the workpiece on the pallet: above the protrusion and between the protrusions of the pallet. Significant differences in properties and structure in these areas are demonstrated. Recommendations on the positioning of the workpiece relative to the pallet protrusions are given. Material properties in the cutting zone above the pallet protrusion and between the protrusions differ significantly. Microhardness values in the zone above the pallet protrusions at the edge are approximately 50% lower than in the zone between the protrusions. As the analysis moves deeper into the sample, the difference decreases. The magnesium concentration is nearly two times lower in the zone above the protrusions than between the protrusions. In the surface layers of the workpiece above the protrusions, the sizes of inclusions are larger than in the depth. This is due to additional quenching of the metal in the workpiece located between the protrusions and prolonged contact with the bath of liquid metal due to difficulties in its removal during cutting on the pallet protrusion. Removing the defective layer by milling to a depth of 0.5 mm neutralizes the difference in the material properties in the zone above the pallet protrusion, between the protrusions, and in the depth.

The potential energy of the equilibrium conformations of metallic nanoparticles has been calculated by the molecular dynamics method. A comparative analysis of methods for obtaining equilibrium nanoparticle shapes has been carried out. It has been found that a minor potential energy variation leads to a noticeable change in the nanoparticle shape.

An Al–Fe–Cr–Co–Ni high-entropy alloy (HEA) coating is deposited on a substrate made of 5083 alloy using the cold metal transfer (CMT) technology (wire-arc additive manufacturing (WAAM) in combination with welding surfacing). The HEA alloy has a nonequiatomic composition. The modern physical materials science methods are used to analyze the structure, phase and elemental compositions, defect substructure of the coating–substrate system. It is shown that he elemental and phase compositions, the defect substructure of the coating are dependent on the distance from the zone of contacting the coating and the substrate. The layer with a thickness to 200 µm adjacent to the contact zone contains includes a second phase at the HEA grain boundaries rich in chromium and iron atoms. The microdiffraction analysis shows that these inclusions are Al₈Cr₅. It is revealed that nanocrystalline phases Al₂O₃ and MgAlO with sizes 10–20 nm and a subgrained structure (subgrain size 140–170 nm) form in the zone of mixing the coating and substrate. The structure of the I type is characterized by inhomogeneous distribution of chemical elements in HEA; there are regions of lammelar shape enriched in Cr atoms and the regions of spherical shape enriched Ni, Fe, and Co atoms. Nanosized (NiCo)₃, Al₄, and Al₁₃Fe₄ particles are arranged along the subgrain boundaries of the system. The physical mechanisms of increasing the material hardness in the coating-substrate contact are discussed.

Nickel‒zinc (Ni‒Zn) and magnesium‒zinc ferrites (Mg‒Zn) and composites based on them are among the most promising radio-absorbing materials that can effectively absorb electromagnetic radiation in the frequency range from several megahertz to several gigahertz. Many questions related to the radio-absorbing properties of these materials still remain open due to the influence of the parameters of a sample on both the frequency dependences of permittivity and on the parameters of domain walls. In this study, a mathematical model of the propagation of electromagnetic waves in radio-absorbing Ni‒Zn ferrites is proposed. The boundary and initial conditions that take into account the geometry and microstructure of the samples are established. The solution of the formulated boundary value problem on a segment using the method of separation of variables or the Fourier method showed that the amplitude of an electromagnetic wave decreases significantly after passing through half the sample thickness, which points out the high radio-absorbing performances of the investigated Ni‒Zn ferrites. The reflection of a plane polarized wave from a Ni‒Zn ferrite/metal plate bilayer in the frequency range of 1–1000 MHz is numerically analyzed. The results of the simulation are verified by the experimental data on the radio-absorbing properties of 1000NN Ni‒Zn ferrites. It is shown that the assumption about the exponential nature of the dependences of the permittivity and permeability on the normalized coordinate is only applicable in a narrow frequency range of up to 3 MHz, in which the experimental and numerical data are in good agreement.

A deeper understanding of the interaction of laser radiation with matter can facilitate the development of technologies for laser synthesis of materials with unique properties, nanostructuring of surfaces of processed solids, etc. The difficulties related to direct observations of various fast processes contribute to the progress in the computer simulation methods used to study them. This work presents the results of the simulation of reduction of the iron surface layer porosity induced by laser pulses. The investigations have been carried out using the potential calculated within the embedded atom method. The model under study has been subjected to structural analysis using the proven algorithms, which makes it possible to quantify the surface area of pores in the bulk of a crystal. The computational cells under consideration contain pores in the amorphous region, which remain stable upon the model cooling corresponding to the natural cooling of a solid in the environment described by a mathematical expression. Obviously, to get rid of defects, a solid should be annealed. It is shown that, after annealing at a temperature of no higher than half of the melting point, pores are preserved. Taking into account that the main mechanisms for reducing the porosity are the diffusion-viscous flow of matter into pores and that diffusion in the amorphous phase is more intense than in the crystalline one, the conditions for slowing down crystallization at a certain temperature should be established in the model. The required conditions have been achieved by straining the computational cell. It is shown that, as a result, the number of pores decreases under both compression and tension.

The results of investigations of the mechanical and thermal properties of the composites modified with a structure-forming agent based on aluminum hydroxide and a high- and low-density polyethylene blend are reported. The properties of the polymer composites, including the fracture stress, relative elongation, melt flow index, heat resistance, thermal stability, and thermomechanics, have been studied. All the composite materials have been based on a titanium dioxide-modified (1 wt %) high- and low-density polyethylene blend (50/50). The aluminum hydroxide content has been varied within 1‒30 wt %. Using the data obtained on the Kanavets device, the temperature dependences of the deformation have been built and the regularities of changes in the thermomechanical curves have been established. It has been shown that, in all the investigated samples, a transition from the solid to viscous-flow state occurs with increasing temperature. The thermal stability has been estimated by the thermogravimetric analysis.

The widespread use of structural aluminum alloys AMg6 and V95 in modern mechanical engineering has led to the identification of such a problem as the non-optimal structure of commercial semi-finished products from these alloys. Traditional types of heat treatment do not always make it possible to correct the structure and obtain a high complex of operational properties. The most common structural defects in commercial semi-finished aluminum alloys containing magnesium and zinc are banding formed by the strengthening intermetallic phase MgZn₂. The structure of magnesium–aluminum alloys has been studied by high-resolution optical microscopy under various heat treatment modes, which include long-term homogenization annealing. The studies were carried out on samples of AMg6 and V95 alloys. For heat treatment, a chamber furnace of the SNOL type equipped with a PID controller was used; the samples were loaded into a furnace preheated to a temperature of 500°C and kept in it for 8 and 16 h. After the exposure was completed, the samples were removed from the furnace and cooled in still air. The hardness was measured on the original samples, samples after heat treatment and 14 days after heat treatment. Studies have shown that an increase in the time of high-temperature holding at 500°C for both alloys leads to the dissolution of intermetallic particles. As a result of the ongoing structural-phase transformations during further cooling and subsequent natural aging, the intermetallic phase again precipitates from the solid solution, as shown by hardness measurements made on the original samples, then after high-temperature annealing and subsequently after natural aging for 14 days.

The paper presents a comparative analysis of the microstructure of diffusion coatings on steels 45 and 38Kh2MYuA obtained by simultaneous diffusion saturation with boron, chromium and titanium. The saturation was performed by packing the saturable samples with sizes of 15 × 15 × 50 mm in a heat-resistant container with a powder saturating medium. At saturation of steel 45, the thickness of the diffusion layer is 120–140 µm, while at saturation of steel 38Kh2MYuA, the thickness of the diffusion coating is in the range of 70–80 µm, which is 58% less. The transition zone of the sample made of steel 38Kh2MYuA contains up to 20 vol % ferrite, while, in the case of steel 45, the transition zone is represented only by pearlite. The maximum microhardness of the diffusion layer on steel 38Kh2MYuA is 1.8 times lower than the indicator of the maximum microhardness of the diffusion layer on steel 45. At the same time, the surface microhardness on both steels is practically the same and is in the region of 1500 HV_0.1. The microhardness of the transition zone in the case of steel 45 is higher than in the case of steel 38Kh2MYuA due to the almost complete absence of the ferrite phase. According to the data of durometric analysis, the thickness of the diffusion layer on steel 38Kh2MYuA does not exceed 85 μm, the thickness of the diffusion layer on steel 45 is 120 μm, which correlates with the results of metallographic analysis. Parts made of 38Kh2MYuA steel strengthened by complex boron–chromium–titanizing, having a lower surface hardness than parts made of steel 45, have high prospects for use as one of the parts that make up the friction pair of critical units. As the second part, it is possible to use boronized steel 45.