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No 3(119) (2024)
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METALS SCIENCE. METALLURGY

6-16 135
Abstract

The paper considers factors influencing the change in hydrogen concentration in forgings made of medium-alloy steels. The computational modeling of the kinetics of changes in the hydrogen content under various variants of preliminary heat treatment is performed. It is shown that it is possible to achieve maximum completeness of hydrogen removal during diffusion processes of austenite transformation under isothermal conditions at the accumulation stage and during direct isothermal annealing (taking into account the increase in the diffusion coefficient of hydrogen in the γ- and α-phases by several orders of magnitude).

17-26 111
Abstract

The paper studies heat treatment effects on the mechanical properties and cold resistance of medium-carbon, medium-alloyed high-strength cold-resistant steels. Kind of changes in strength and plastic properties depending on the tempering temperature have been revealed. It has been established, that tempering in the temperature range 560–580°C provides an optimal combination of strength and plastic properties and makes it possible to increase the cold resistance of the steel.

27-36 77
Abstract

Dispersion-strengthened composite materials belong to the group of promising structural materials characterized by a diverse combination of properties. The work presents examples of the creation and heat treatment of composite materials based on aluminum alloys, strengthened by a dispersed phase of titanium carbide, and characterized by high hardness, elastic modulus and good wettability by the melt. The most accessible, inexpensive and effective way to obtain them is self-propagating high-temperature synthesis (SHS).

The work shows the possibility of obtaining new aluminum matrix composite materials based on industrial aluminum alloys AM4.5Kd and AK10M2N by reinforcing them with 10 wt.% highly dispersed titanium carbide or AM4.5Kd–5.95 vol.% TiC and AK10M2N–5.78 vol.% TiC. The reinforcing phase is formed in alloy melts using the technology of SHS from the initial elemental components—titanium powder and carbon black. Using the obtained samples, an assessment was made of the uniformity of the ceramic phase distribution over the volume of the matrix alloys, which amounted to 0.15 and 0.12 for the samples AM4.5Kd–10%TiC and AK10M2N–10%TiC, respectively, which constitutes a high degree of uniformity.

An assessment was made of physical properties such as porosity, density, electrical conductivity, as well as the coefficient of thermal linear expansion. Analysis of the data allows us to say that the final composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC have a slightly higher density (↑~4%) than the matrix alloys, due to the presence of a ceramic phase, low porosity values (~1%), lower TCLE (↓~6%) than matrix alloys and low electrical conductivity (~25% IACS). This article also presents data on the values of the mechanical properties of composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC. It has been shown that reinforcement with a ceramic phase contributes to a significant increase in hardness by 15 and 42 HB, as well as higher values of the compressive yield strength by 31 and 17 MPa, respectively, while maintaining a high level of relative deformation. The results obtained allow us to conclude that the developed composite materials can be recommended for products used under conditions of elevated temperatures and significant wear.

37-45 75
Abstract

The results of plastic compression of steels and alloys of different chemical compositions at temperatures and rates of plastic deformation corresponding to common thermomechanical treatment (TMT) regimes are considered. The features of the diagrams σ (ε, έ, Т) are revealed. The processes of strain accumulation and thermal dissipation are accompanied by structural rearrangements. Depending on the chemical composition and hot compression modes, structural transformations occur self-organized, with the possibility of excitation of oscillations and the formation of dissipative solitons.

FUNCTIONAL MATERIALS

46-56 124
Abstract

The effect of proton irradiation with a power of 1·1017 units/cm2 and an energy of 2 MeV on the structure and properties of composite ceramics of the composition ZrO2–SiO2–Al2O3 is shown. It has been established that at this irradiation dose, the phase composition of the ceramic does not change. Calculations using X-ray diffraction methods have shown that proton irradiation creates compressive stresses (stresses of the 1st kind) ranging from ~–1 to –2 GPa on the surface of field ceramics, while microstresses (stresses of the 2nd kind) are practically absent. Analysis of SEM images of the ceramic surface after irradiation showed a chaotic arrangement of macropores in the t–ZrO2 matrix, while pores in zircon particles are located exclusively along the boundaries of inclusions. A decrease in the level of hardness and density in ceramics after proton treatment was noted due to the formation of a large number of pores.

57-71 87
Abstract

The paper considers one of the insufficiently explored methods for the synthesis of compounds of the homologous series TinO2n–1, in particular the method of hydrogen reduction. A series of samples (n = 2–8) were obtained from initial TiO2 powders of various chemical purities (99.0–99.99%) with modification with rutile in a wide range of temperatures and reduction times in a hydrogen environment. The influence of the purity of the initial samples, temperature and recovery time on the structure of the resulting compounds was established. Differences in the crystal structure of compounds of the homologous series TinO2n–1, as well as β- and λ-polymorphic modifications of Ti3O5, are shown. An approach to selecting the temperature and time of reduction of TiO2 powders to obtain a specific phase in compounds of the homologous series TinO2n–1 is substantiated.

72-83 106
Abstract

AlMgB14 ceramics is known as a material characterized by increased hardness in combination with a low friction coefficient. Composite structures based on this ceramics have even higher strength characteristics. In the present work, we investigate the structural-phase states and physicomechanical properties of composite ceramics of the AlMgB14–TiB2 system with a variable TiB2 content, obtained by hot pressing the initial batch based on AlMgB14 and TiB2 ceramic powders preliminarily synthesized by the method of self-propagating high-temperature synthesis. It was found that the resulting materials are characterized by a composite structure represented by TiB2 inclusions distributed in the AlMgB14 matrix. The phase composition of the resulting composites is similar to the phase composition of the initial batch, with 5 to 9 wt. % of the MgAl2O4 spinel phase being formed. The microhardness of AlMgB14–TiB2 composites is up to 19.9 GPa (the hardness of AlMgB14 ceramics obtained by a similar method without additives is 7 GPa). The three-point bending strength of AlMgB14–TiB2 composite materials is 309 MPa.

84-92 111
Abstract

The technology of applying composite intermetallic coatings of the Ni–Ti system reinforced with carbides based on powders (SiC, WC, B4C) on the surface of titanium alloy plates with the sequential use of the CGDN method and laser processing is considered. The technological parameters of the laser-thermal processing, ensuring the production of composite coatings of the Ni–Ti–(SiC, WC, B4C) system of high hardness, are determined.

93-101 76
Abstract

The paper studies coatings of the Ni–W system alloyed with molybdenum and cobalt obtained by electrodeposition. The effect of the concentration of salts of the alloying element in the electrolyte on the chemical composition of the coatings was studied under various synthesis conditions. All the obtained coatings are nanocrystalline or amorphous solid solutions of tungsten, molybdenum or cobalt in nickel with a FCC crystal lattice. Polarization measurements made it possible to establish that the most resistant to corrosion in a 3.5% NaCl solution is a coating containing 35% W and 8% Mo.

102-111 110
Abstract

The paper describes the structural and phase composition of TiHf50, AlHf50, TiAl49Hf2 composite materials obtained by the “hydride” technology. A three-component phase diagram for Ti-Al-Hf at 1150°C is constructed. The structural state of TiAl49Hf2 alloys was predicted based on reference lattices found in the USPEX code with the VASP interface; quantum-chemical calculations of the TiAl49Hf2 energy were additionally performed in the CASTEP code. It is shown that solid solutions dominate in the TiAl49Hf2 alloy sample, in which the main elements dominate: Al10 – Ti9Al23 – Ti8. Hf atoms can be introduced into the interstitial sites [-0.257 0.042 0.2545] (St-Hf-27), [0.0053 -0.0120 -0.0765] (St-Hf-143), [0.5 0.5 0.5] (St-Hf). The introduction of hafnium into the specified lattice sites does not violate the stabilizing effect in the TiAl49Hf2 systems. It is shown that the maximum microhardness value (4.9 GPa) was obtained when testing the TiHf50 sample (for comparison: for the TiAl50 system – 1.2 GPa, for the TiAl49Hf2 system – 2.2 GPa).

112-121 80
Abstract

The structural and phase composition of TiZr50, AlZr50, TiAl49Zr2 composite materials obtained by the hydride technology was investigated. A model three-component phase diagram was constructed for Ti–Al–Zr at a temperature of 1150°C. The structural state of TiAl49Zr2 alloys was predicted based on reference lattices (USPEX code with VASP interface), quantum-chemical calculations of the energy of TiAl49Zr2 were carried out in the CASTEP code. Solid solutions dominate in TiAl49Zr2, in the composition of which the main elements are predominant: Al10–Ti9Al23–Ti8. Zr atoms can be introduced into the interstitial sites [– 0.257 0.042 0.2545] (St–Zr–27), [0.0053–0.0120–0.0765] (St–Zr–143), [–0.3251–0.3983 0.4880] (St–Zr– 75). The introduction of Zr into the specified lattice sites does not violate the stabilizing effect in the TiAl49Zr2 systems. All reference lattices are stable. In the TiAl49Zr2 alloy, the main phases are Al10Ti9Zr, Al23Ti8Zr, the contributions of which to the theoretical intensity are 78.57 and 21.43%. In the AlZr50 sample, the phases ZrAl, Zr2Al3, ZrAl2.

122-132 146
Abstract

The paper presents experimental data on the physical and mechanical properties of cellular materials with the geometry of triply periodic minimal surfaces (TPMS). It has been established that the dependence of the strength and Young’s modulus on the relative density of materials with the TPMS geometry corresponds to the Gibson – Ashby equation with a fairly high accuracy. Such materials are superior in mechanical properties to classical cellular materials and have high isotropy of mechanical properties.

133-144 93
Abstract

The physical properties (thermal and thermal diffusivity) of thermal interfaces based on powdered boron nitride with a hexagonal crystal lattice (h-BN) and copper with a cubic crystal lattice (Cu) for cooling the electronic component base of micro- and nanoelectronics are studied. The physical properties are determined by the flash method. The prospects of using pressed hexagonal boron nitride powder as a thermal interface without using a binder are described. A comparison with the physical properties of other thermal interfaces that are widely used at present is made.

POLYMERIC COMPOSITE MATERIALS

145-152 87
Abstract

Diopside is one of the key components in various construction materials and can also be used as a filler for epoxy compositions. However, due to the complexity and labor intensity of developing domestic deposits of this calcium magnesium silicate, it is rational to synthesize diopside based on rice husk ash and dolomite and compare its phase composition and properties with diopside concentrate mined in nature.

It has been established that the synthesized calcium-magnesium silicate, compared to the natural mineral, contains 10 times more diopside, has a 3 times smaller pore volume and an almost 5 times smaller average particle size, i.e. they differ significantly in both phase and granulometric composition, as well as in porosity.

At the same time, both natural and synthetic diopside-containing fillers increase the hardness, wear resistance and viability of epoxy compositions. A filler synthesized on the basis of rice husk ash is more effective in terms of increasing the performance characteristics of epoxy materials.

STRUCTURAL-WORKING STRENGTH AND SERVICEABILITY OF MATERIALS

153-168 61
Abstract

The first part considers the main physical and mechanical processes occurring under tension of round bars. The procedure is presented that allows one to describe the plastic strain effect on the critical brittle fracture stress in probabilistic statement. The main statements of Prometey model for prediction of fracture stress are also presented. The investigations are carried out for two materials: 2Cr–Ni–Mo–V steel used for WWER-1000 RPV in the thermally-embrittled state and low-alloyed low-strength steel of St3 grade taken as model material ruptured by cleavage up to plastic strain up to 50%.

169-186 57
Abstract

The second part of the paper presents the results of uniaxial tension testing of smooth round bars of 2Cr–Ni–Mo–V steel in the thermally-embrittled state and St3 steel in the initial state. SEM examination of the fracture surfaces is carried out. The brittle fracture probability is calculated using the Prometey model presented in the first part of this article. It has been found that the plastic strain effect on the microcrack propagation probability is caused by two reasons: (1) the critical brittle fracture stress increase due to formation of new barriers for microcrack under plastic deformation, and (2) the working volume decrease due to the neck formation in tensile round bar. A unified set of parameters has been proposed to take into account the plastic strain effect on cleavage microcracks propagation probability for WWER-1000 RPV steel and low-alloyed low-strength steel.

CORROSION AND PROTECTION OF METALS

187-195 79
Abstract

The article presents the results of studying the effect of lanthanum, cerium and praseodymium additives (0–1.0 wt.%) as structure modifiers on the anodic behavior of the aluminum conductive alloy AlTi0.1 in the NaCl electrolyte medium. The studies were carried out using the potentiostatic method with a potential scan rate of 2 mV/s. It was found that over time, the free corrosion potential of the alloys shifts to the positive side and acquires a positive value with an increase in the modifier concentration (lanthanum, cerium, praseodymium) in the aluminum conductive alloy. The addition of lanthanum to the aluminum conductive alloy AlTi0.1 by 12–23%, cerium by 20–30% and praseodymium by 25–35% increases its corrosion resistance. An increase in the corrosion rate of the alloys with an increase in the NaCl concentration in the solution, regardless of their composition, was noted. An increase in the concentration of chloride ion in the NaCl electrolyte leads to a decrease in the potentials of free corrosion, repassivation and pitting of alloys.

196-209 88
Abstract

The paper examines electrochemical studies of forgings made of α, pseudo-α titanium alloys of industrial compositions and with the addition of ruthenium. Comparative dependences of the current density on time were constructed at various potentials in 3.5% NaCl for titanium alloys of industrial composition and with the addition of ruthenium. The breakdown potential of the titanium alloys under study was determined. Microstructural studies of titanium alloys of various compositions were carried out after determining the breakdown potential.

RADIATION MATERIALS SCIENCE

210-220 82
Abstract

Safety assurance of spent nuclear fuel dry storage requires reliable prediction of mechanical properties of fuel element cladding depending on structural changes at all stages of nuclear fuel handling. In this work investigations of hydrides structure in irradiated fuel element cladding made of E110 alloy have been conducted in irradiated state as well as after tests simulating dry storage conditions. Using the program code, the coefficients that best correlate with mechanical properties have been found.



ISSN 1994-6716 (Print)