No 4 (2021)
- Year: 2021
- Articles: 10
- URL: https://vektornaukitech.ru/jour/issue/view/30
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Description:
Published: 30.12.2021
Full Issue
The study of mechanical deformation resistance of α-Ga2O3 epitaxial layers using the nanoindentation technique
Abstract
Gallium oxide (Ga2O3) is a wide-band semiconducting material with an energy gap width Eg=4.8–5.0 eV, high conductivity (λ~10.9–27.0 W/(m·K)), and radiation and chemical resistance. Its energy gap width and conductivity allow in the future using the material in the structures of power equipment and optoelectronic devices to increase their energy performance, i.e. to decrease heating and increase productive capacity. Radiation resistance, high breakdown field, and optical asymmetry of Ga2O3 make it attractive for application when designing UV-photoelectric receivers and space systems. The electrical and optical properties of Ga2O3 are amply studied, but there are no systematic data on its physical and mechanical properties (hardness, Young’s modulus, and crack resistance). The paper investigated the deformation in α-Ga2O3 epitaxial layers during nanoindentation. For indentation, the authors used NanoTest (Micro Materials Ltd.) hardness meter. The surface (0001) of α-Ga2O3 crystalline layers produced in the process of chloride gas epitaxy on sapphire (Al2O3) substrates with basic (0001) orientation was investigated. For the first time, the authors experimentally obtained the values of α-Ga2O3 hardness and Young’s modulus using the Oliver-Farr method. The dependences of the indentation load on the penetration depth demonstrated the deviation from linearity, including stress relaxation coming from the pop-in phenomenon. The average values of nanohardness H and Young’s modulus E were 17 and 281 GPa, respectively. The obtained H and E values demonstrate higher characteristics compared to the formerly studied β-Ga2O3 epitaxial layers. This discrepancy can be explained by the more close-packed arrangement of the α-Ga2O3 structure (the corundum type) than one of monoclinic β-Ga2O3. The study shows that α-Ga2O3 leaves the majority of semiconducting materials behind in its mechanical properties conceding only to gallium nitride (GaN) and sapphire (Al2O3).
7-16
The influence of method and temperature of ion-plasma treatment on physical and mechanical properties of surface layers in austenitic stainless steel
Abstract
Ion-plasma saturation with interstitial atoms (nitrogen or carbon) is a promising method for enhancing the surface strength and wear resistance of austenitic stainless steel parts and products. The paper considers the influence of method and temperature of ion-plasma treatment (IPT) on phase composition, thickness, and strength properties (microhardness) of the surface layers in 01H17N13M3 austenitic stainless steel specimens. Steel specimens with a coarse-grained structure were nitrided in the arc and glow discharge plasma at different temperatures (400 °C, 550 °C, and 700 °C). Regardless of temperature and IPT-method, ion-plasma nitriding leads to the formation of hardened surface layers in steel specimens. In this case, the thickness and phase composition of IPT-hardened layers depend on both the method and temperature of nitriding. Nitrogen saturation of specimen surfaces in the glow discharge at a temperature of 400 °C promotes the formation of a thin S-phase layer (nitrogen-expanded austenite, 4 μm in thickness). At the same IPT temperature in the arc discharge plasma, the authors observed the formation of a heterophase (Fe-γN, Fe4N, CrN, and Fe-α) surface layer with a significantly greater thickness (40–45 μm). Regardless of the IPT-method, a saturation of specimens at temperatures of 550 °C and 700 °C is accompanied by the formation of thick heterophase hardened layers (40–60 μm). In this case, the IPT method has a negligible effect on the phase composition of layers but significantly affects the ratio of the volume content of the hardened phases. After being IPT-processed in different modes, the microhardness distribution profile for all specimens has three typical zones: a composite layer (or S-phase at the IPT in a glow discharge at Ta=400 °C), a diffusion zone, and a matrix. With an increase in the saturation temperature, the thickness of the transition diffusion zone increases regardless of the IPT method.
17-26
Resiadual stress relaxation in decahedral particles through the formation of a central spherical void
Abstract
Small metal particles with a body-centered crystal lattice (BCC) often take the form of polyhedrons with fifth-order symmetry axes such as the icosahedron, decahedron, and pentagonal prism. The quintic symmetry axes, forbidden by the traditional crystallography laws, cause inhomogeneous elastic stress and strain in these particles. Under certain conditions, these stress and strain could relax through the change in the particle structure: the formation of partial and perfect dislocations, misfit layers, and the nucleation of cracks and voids. Within the quasi-equilibrium energy approach, the authors proposed a theoretical model of residual stress relaxation in decahedral particles due to the formation of a central spherical void. The explicit analytical expressions for energies of solid and hollow decahedral particles are found. The elastic energy of a hollow decahedral particle is defined as the work spent on the nucleation of a positive wedge disclination with the power ω≈0.0163 rad (≈7°20') in the elastic spherical shell under its own stress field. The authors determined the change in the surface energy due to the formation of a void considering the influence of the relaxation effect of the first coordination sphere surrounding the vacancy on the particle volume change. The energy change of decahedral particles during the formation of a spherical void is calculated and the optimal and critical parameters of this process are determined. The study shows that there some critical radius of a particle, if reached the formation of the central spherical void becomes energetically favorable. Moreover, the study shows that a pore germ will grow until it reaches a certain optimal size corresponding to the greatest change in the system energy. The numerical calculations correspond with experimental observations of unstable voids in the rather small silver and gold decahedral particles with the diameter of 30–40 nm and stable voids in relatively large copper decahedral particles with the diameter of ~1 μm.
27-38
Specific features of structural-phase transformations and hardening during shear deformation under pressure of high-nitrogen steel with austenitic-ferritic structure of metal matrix
Abstract
The increased anticorrosive, strength, tribological, and physical characteristics are the specific features of steels with high nitrogen content. Searching for the ways to strengthen high-nitrogen steels is a promising area of contemporary metal science. Heat treatment is one of the methods of hardening nitrogen steels as a result of precipitation hardening with nitride particles. The authors studied the influence of short-term high-temperature aging and large plastic deformations implemented by shear under the pressure of 8 GPa (SP method) on Bridgman anvils (three revolutions of anvils with the rotation velocity of 0.3 rev/min) at room temperature on the structural-phase transformations and micromechanical properties of the 08H22GA1.24 high-nitrogen steel with the mixed γ (austenite) + a (ferrite) metal matrix structure. The study identified that aging (0.5 h) at the temperature of 650 °С of steel quenched at the temperature from 1180 °С causes the formation of the mixed austenitic-ferritic structure of metal matrix in the ratio of 50 vol. % of g and 50 vol. % of α and the release of extended secondary Cr2N chromium nitrides, together with ferrite interlayers forming the areas with the pearlite-like structure. These areas cause the increased microhardness of steel with the austenitic-ferritic matrix structure (385±8 HV 0.025) compared to one of steel aged at the temperature of 550 °С (0.5 h) and having an austenitic matrix structure strengthened with secondary CrN nitrides (364±8 HV 0.025). The SP deformation of steel aged at the temperature of 650 °С (0.5 h) with the initial g+a+Cr2N structure leads to g→aʹ transformation and the formation of submicro- and nanocrystalline structures. It causes the effective strength improvement of steel (up to 900±29 HV 0.025) and the growth of resistance to elastoplastic deformation compared to aged at the temperature of 550 °C (0.5 h) condition.
39-47
Combination of circular motions in machines and mechanisms
Abstract
In technical systems, including aviation and space technology, and in particular, in aircraft transmissions, bearings, orbital systems, helicopter mechanisms, and many others, the combined rotational movements are widespread, and when designing, it is important to understand the nature of joint motion. The paper aimed at the generalization of the principle of the combination of motions in circular movements. The author considered the x'0'y' coordinate system that rotates in the x0y coordinate system without angular acceleration with the velocity ω. The radius of rotation is equal to ρ1. Wherein 0x || 0'x', 0y || 0'y'. An object a rotates in the x'0'y' coordinate system without angular acceleration with the velocity ±ω. The radius of rotation is equal to ρ2. The study identified that at reverse rotations, the trajectory of joint motion represents an ellipse. The author determined all standard ellipse characteristics relating to the case under the study and identified the elliptical trajectory inclination. The study shows that if the joint motion trajectory is elliptical and the semi-axes are equal (ρ1+ρ2) and |ρ1−ρ2|, then an object a undergoes circular motion in the x'0'y' coordinate system without angular acceleration with the velocity −ω. Just as the result of the superposition of two non-accelerated straight movements is also non-accelerated, i.e. a uniform and rectilinear movement, at the one-way rotations, the joint motion trajectory represents a circle. At circular motions with multiple speeds, the joint motion trajectory represents a snail. The practical aspect of the study is determined by the fact that the resulting formulas can be directly used in the CAD system when performing design works.
48-56
Special aspects of arc welding of a laminated corrosion-resistant material
Abstract
The paper shows the demand of the chemical industry for corrosion-resistant materials, as well as the prospects of the creation of laminated metal materials with internal protectors (LMM with IP). The authors offer the architecture and composition of layers of LMM with IP ensuring stable operation within the highly aggressive environment. The study identified the possibility of improving corrosion resistance ten and more times compared to high-alloy austenitic stainless steels. The authors show the efficiency of the application of explosion welding to produce LMM with IP. The paper considers the example of the production of a four-layer material with one internal protector made of low-alloyed, low-carbon steel of the following architecture: 2-mm layers of 12H18N10T + 09G2S + 12H18N10T plates of steel and the base 10-mm layer of 09G2S. The authors developed the process diagrams for performing butt-welded joints of such material, identified special aspects of the formation of its microstructure and properties. To obtain the maps of specific chemical elements distribution in the layers and interlayer boundaries, the authors used the energy-dispersive microanalysis method. Peculiarities of corrosion damage of a welded seam and weld-adjacent area are studied. The study showed the necessity of using a facing layer in a welded seam. Microstructural, X-ray tomographic, and gravity-measuring studies proved the obtained results. To evaluate the quality of welded joint, the authors performed the corrosion tests of a welded seam and weld-adjacent area, carried out visual inspection control and X-ray tomography. The corrosion tests were carried out using 10-% III ferrous chloride water solution. The paper presents the results of the static bending tests of a welded joint. The absence of fracture, lamination, and cracks served as an estimation criterion. The study identified the possibility of obtaining a defect-free welded joint of LMM with IP with high corrosion resistance and advanced mechanical properties.
57-68
The study of temperatures in a tungsten electrode at reverse polarity arcing
Abstract
The paper considers the features of energy release in a tungsten electrode under the reverse polarity TIG welding. The study substantiates the statement that the chemical composition of an electrode does not significantly affect the transfer of anode power to it. The specific effective power of an electrode is substantiated and taken as 6 W/A. The authors analyzed the features of arcing on the flat tip of a 3 mm diameter electrode using high-speed video. The analysis identified that at limiting currents ensuring tip melting, the tip heating is uniform over the cross-section. As a design scheme, the authors selected a continuous flat heat source on the semi-infinite rod surface with surface heat transfer. The authors obtained averaged values for volumetric heat capacity сρ=3.2 J/(cm3∙°С) and heat transfer coefficient а=0.3 cm2/s. The current at which the tip melting temperature is reached was taken as a limiting current. Using the limiting current value and start time of the electrode tip melting, the authors calculated the electrode heat transfer coefficient value b. The calculated melting depth for the over-limiting current welding mode showed good coincidence with an experiment. The authors recalculated the b value for the electrodes of 4-, 5-, and 6-mm diameter and calculated limiting currents for these diameters. The design limiting currents for these diameters also showed good coincidence with experimental results. The study showed that the increase of a coefficient up to 0.4 cm2/s does not cause changes in temperature and limiting currents at simultaneous сρ adjustment according to the constant thermal and physical properties сρа0.5. As a result, the authors obtained temperature dependencies for the electrode over time and length. Time dependence of the electrode tip heating allows calculating limiting currents with the decrease in arcing time.
69-79
Effect of nanostructuring frictional treatment on micromechanical and corrosion properties of stable austenitic chromium-nickel steel
Abstract
Friction treatment is an effective method to increase the strength and wear resistance of austenitic chromium-nickel steels. Previously, the authors identified that the high level of mechanical properties of metastable austenitic steels is achieved at the intensive development of deformation γ→α'-transformation. However, the presence of deformation martensite in the austenitic steel structure can negatively affect its anti-corrosion properties. The search for ways to improve the strength characteristics of stable austenitic chromium-nickel steel while maintaining high resistance to corrosion destruction is the up-to-date line of research. In this paper, to evaluate the mechanical properties of 03Cr16Ni14Mo3Ti steel in the hardened condition and after friction treatment, the authors applied the technique of measuring the hardness using the restored print and the method of instrumental micro-indentation, which allows recording the indenter loading and unloading diagrams. The corrosion failure resistance of steel was studied in general corrosion tests. The authors compared the corrosion rate of austenitic steel after grinding, electropolishing, and friction treatment; using scanning electron microscopy and optical profilometry, studied steel surfaces subjected to these treatments and determined their roughness. Nanostructuring friction treatment provides surface hardening of stable austenitic steel up to 570 HV 0.025. The study showed the high efficiency of friction treatment application to increase the strength characteristics and resistance of steel surface layer to elastic and plastic deformation. The authors identified that austenitic steel is characterized by similar corrosion rates km=(3.26-3.27)∙105 (g/cm2∙h) after electrolytic polishing (the structure of large-crystal austenite) and after frictional treatment (sub-micro/nanocrystalline austenite structure), while mechanical grinding leads to a twofold increase in the corrosion rate of 03Cr16Ni14Mo3Ti steel due to the occurrence of microcracks and metal breakouts on the polished surface. The research justified the determining role of the quality of the surface formed by various treatments (roughness, the presence of continuity defects) in ensuring the corrosion resistance of stainless steel.
80-88
The influence of boron carbide additive on the structure and hardness of a nickel-based coating
Abstract
Laser cladding is increasingly frequently used in various branches of mechanical engineering since it has such advantages over traditional methods of depositing coatings as high heating and cooling rates and minimal mixing of base and melting materials. Laser-clad coatings are usually characterized by a fine-grained structure and a minimal heat-affected zone. Coatings formed from the Ni–Cr–B–Si powders are also very common in industrial applications, as they have good resistance to wear, corrosion, erosion, etc. Various strengthening particles can be added to this group of powders to improve the properties of the deposited coating. Boron carbides can act as such particles since they have high hardness, thermodynamic stability, and wear resistance. In this regard, the paper investigated the influence of the 7 wt. % of boron carbide B4C addition on the structure and hardness of the NiCrBSi coating formed by laser cladding of PG-SR2 powder on the surface of 30HRA steel. Using the scanning electron microscope, the authors carried out microscopic studies of the structure of NiCrBSi and NiCrBSi–B4C coatings and presented the results of X-ray spectral microanalysis. The study shows that the structures of both coatings in the deposited state are characterized by uniformity and fine-grain structure. The investigation revealed that the samples with NiCrBSi and NiCrBSi–B4C coatings have a narrow transition zone from the deposit to the base metal. The paper presents the results of measuring the microhardness of coatings indicating a decrease in the microhardness of laser-clad nickel-based coatings with the boron carbide addition.
89-97
Optimal scheme of laser hardening of a tool wedge tip
Abstract
Laser heat treatment is one of the effective methods to improve the operational characteristics of metal-cutting tools. In the practice of laser hardening, there are several methods to select treatment mode: experimental, calculated, and according to reference data. The finite element method is promising for estimating the treatment zone parameters, and its application is the most in-demand for calculating the temperature field of a geometrically complex tool. When organizing the hardening process, the selection and setting of processing modes for the cutting wedge tip are the most difficult. In this regard, the solution for the multifactorial problem of optimizing the hardening scheme of an area near the tool tip is relevant when designing and automating the process of blade tool laser hardening. Using the finite element method in the ANSYS Workbench software, the authors carried out the numerical experiments to optimize the laser hardening scheme of the tool cutting wedge tip on the example of an instrument with a wedge angle equal to 60°. The paper considers three variants of the hardening scheme. The first variant is the implementation of multiple processing of an area adjacent to the tool tip. The second one consists of alternate movement of laser treatment spots along the cutting edges within the tool tip area. According to the third variant, the treatment spots were sequentially located along the bisector of an angle at the tool tip. The study showed that, according to the maximum depth criterion, an optimal hardening scheme is a scheme, which consists of alternate movement of laser treatment spots along the cutting edges in the tool tip area. In this case, the hardening zone characteristics are ensured that exceed similar values describing the hardening zone for other laser treatment options for the tool cutting wedge tip.
98-106