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Vol 120, No 10 (2019)
- Year: 2019
- Articles: 16
- URL: https://journals.rcsi.science/0031-918X/issue/view/10295
Electrical and Magnetic Properties
Specific Features of the Magnetocaloric Effect in a Uniaxial Paramagnet with Kramers Ions
Abstract
The changes in magnetic entropy upon isothermal magnetization of a uniaxial paramagnet with Kramers ions (spin S = 3/2) and single-ion easy-plane anisotropy were studied at low temperatures. It was demonstrated that the magnetocaloric effect upon magnetization in the easy direction is considerably stronger than the one corresponding to magnetization in the hard direction (perpendicular to the easy plane). It was found that magnetization in the hard direction is accompanied by an anomalous increase in magnetic entropy in a finite interval of magnetic fields. A nonmonotonic dependence of entropy on the final magnetization field is produced as a result.
925-929
Magnetic State and Phase Composition of Co3C Nanoparticles
Abstract
Nanoparticles Co3C were prepared using solid-phase synthesis under high pressure. The phase composition of the nanoparticles has been analyzed; the magnetization has been measured and 59Со NMR spectra in a local field have been recorded. It is shown that Co3C is a ferromagnet with the Curie temperature TC = 498(10) K. The hyperfine fields and components of electric field gradient tensor were determined for two nonequivalent Co positions in the carbide. The obtained hyperfine fields correspond to the spin state of Co ions S = 1.
930-935
Structure, Phase Transformations, and Diffusion
Influence of Vanadium Microalloying on Isothermal Transformation Behavior of Eutectoid Steel
Abstract
Abstract—The influence of vanadium as a microalloying element on the austenite decomposition behaviors and microstructure transformation of eutectoid steel were studied during isothermal cooling. Vanadium dissolved in γ matrix exhibited a negative effect on austenite decomposition to pearlite microstructure and led to a decrease in the lamellar spacing. Moreover, the results indicated that the dissolved vanadium segregated toward austenite grain boundaries and suppressed the formation of grain boundary ferrite. However, the precipitation of vanadium during the isothermal process led to a decrease in vanadium dissolved in matrix that indirectly promoted transformation to pearlite. The precipitates could act as nucleus for pearlite formation, which also accelerated the transformation. The lamellar spacing of pearlite increased as a result of carbon consumption of precipitates. The addition of nitrogen remarkably accelerated the transformation, because the chemical driving force for VN formation was significantly larger.
936-942
Structure and Phase Composition of Sputtered Films of Hafnium–Carbon Alloys
Abstract
Ion-plasma sputtering and codeposition of ultrafine particles of hafnium and carbon were used to produce film coatings in the concentration ranges of 5.3–59.8 at % C. Structural investigations revealed the existence of Hf–C solid solutions in the concentration range of 5.3–11.5 at % C. In the concentration range of 21.5–59.8 at % C, the coatings consist of the hafnium-carbide phase; and at 16.2 at % C, both phases coexist. The lattice parameters of the phases present in the films and their variation depending on the carbon concentration have been determined. The dependence of the HfС lattice parameter in the range of 16.2–35.0 at % C on the nature of the substrate on which the coating is deposited has been established. The solid solutions of carbon in hafnium exhibit conductivity of metallic type; the resistance of the hafnium carbide almost does not change upon cooling from 300 to 11 K. The direct synthesis of hafnium carbide HfC by a codeposition of nanoparticles on the surface of products can be used as a technological method.
943-948
Recrystallization Kinetics of Niobium with Submicrocrystalline Structure
Abstract
Abstract—Transmission and scanning electron microscopy have been used to study the kinetics of recrystallization at 400 and 700°C of niobium in which a submicrocrystalline structure was created as a result of high-pressure torsion. It has been shown that the recrystallization at 700°C occurs in accordance with the kinetics of normal grain growth. A decrease in the rate constant with an increase in the duration of annealing to more than 1 h is due to textural changes, rather than the completion of primary recrystallization. Upon the low-temperature recrystallization (400°C), a stable fine-grained structure is formed, which remains almost unchanged with increasing duration of annealing.
949-955
Ferritic Decomposition in Fe–36Ni–3Cr Invar Alloy
Abstract
Nickel redistribution and austenite decomposition into ferrite with the formation of up to 15% α‑ferrite crystals 10–100 nm in size in a fairly stable Fe–36Ni–3Cr invar alloy were found. The austenite decomposition during heating in a 250–400°C temperature range is intensified by preliminary strong plastic deformation by rolling or shearing under high pressure.
956-961
Effect of Annealing on the Structure of Metallic Diffusive Membrane Filters on the Base of Palladium
Abstract
Abstract—The metallic filter foils of palladium-yttrium alloys are studied using X-ray diffraction analysis. The aim of the research is to study the high-temperature effects on phase transformations in palladium-based alloys. The change in the phase composition of the alloy and in its subsystems of defects were found upon the additional annealing of one of the membranes. A decrease in the microstrains was estimated by the change in the diffraction-reflections smearing after the annealing. The formation of regions with an increased lattice parameter in comparison with that of the matrix structure and effects of the high-temperature annealing on the structure of these regions are discussed.
962-968
Formation of the Structure and Properties upon Thermohydrogen Treatment of the Alloy Based on Titanium Aluminide Ti2AlNb
Abstract
Abstract—Changes in the structure, phase composition, microhardness, and modulus of elasticity upon thermohydrogen treatment of the VTI4 alloy based on the orthorhombic titanium aluminide Ti2AlNb alloyed with hydrogen to 12.5 at % have been studied using electron microscopy, X-ray diffraction analysis, and microindentation. It has been shown that the alloying of this alloy with hydrogen leads to a decrease in peak stresses and to an increase in the degree of deformation to the formation of cracks in the course of upsetting at 900°C. The kinetics of dehydrogenation at the temperatures of 600 and 700°C for 4 h in an argon flow and in vacuum has been studied. The thermohydrogen treatment of the VTI4 alloy makes it possible to obtain a thermostable state with a safe hydrogen content with a predominance of the O phase in the structure and high physical and mechanical properties (the Vickers hardness up to 5300 MPa, the contact modulus of elasticity to 114 GPa) after the final dehydrogenating annealing in the vacuum at 600°C for 4 h.
969-975
Mechanical Properties of Tube Steel after Full Hardening with Austenite Stabilization
Abstract
The stabilization mechanism of residual austenite in high-alloyed steel with 13% chromium content upon quenching partitioning treatment is studied in this work. It is established that the mechanical properties after such thermal treatment are caused by the opposite stabilization and tempering effects and largely depend on the position of the cooling stop temperature relative to the martensitic point, which determines the amount of both stabilized austenite and martensite tempered at the same temperature.
976-980
Strength and Plasticity
Modeling of Wear Behavior of Al–Si/Al2O3 Metal Matrix Composites
Abstract
Artificial neural network (ANN) approach, analysis of variance (ANOVA), and multiple regression model were developed to predict the wear rate for the aluminum (Al)-silicon (Si) alloy. These methods were based on weight fractions of alumina (Al2O3), load, and sliding distance as inputs. Metal matrix composites (MMCs) were prepared using stir casting method. The Al–Si alloy was reinforced with the addition of 0, 10, 15, 20, and 25 wt % of Al2O3 particles. The ANN model was utilized to predict the wear rates of the composites. Experimental results indicated that the increase of both load and sliding distance increases the wear rate. However, the increase of weight fractions of alumina (Al2O3) decreases the wear rate. Both ANN and ANOVA revealed that the sliding distance has the major influence on the wear rate in comparison with the factor of alumina weight fraction. However, the applied load has a relatively low influence on the wear rate of Al–Si/Al2O3 composite. A multiple regression approach suggested in this study reveals the correlation between the weight fractions of Al2O3, load, and sliding distance and the wear rate.
981-988
Effect of The Processes of Self-Tempering and Tempering on The Mechanical Characteristics and the Character of Fracture of Low-Carbon Martenstic Steel Quenched in Air
Abstract
Abstract—The influence of the processes of self-tempering and tempering on the mechanical characteristics and structure of low-carbon martensitic steel after air-quenching has been considered in this work. The processes of martensite decomposition (self-tempering) that started upon cooling continue in the steel in the course of subsequent tempering at 200, 300, 400, and 500°C with the formation of a ferrite–carbide mixture of different degrees of dispersion. Upon tempering at temperatures of 200–400°C, a monotonic increase is noted in the yield stress by 11%; the tempering at 500°C leads to a 3% reduction in the yield stress. The character of the fracture of the samples was studied using scanning electron microscopy; this study has confirmed the phenomenon of temper brittleness in the steel at temperatures of 300 and 500°C, which is in good agreement with the results of mechanical tests.
989-994
Atomistic Modeling of Stacking Faults in Cementite. Planes Containing Vector [001]
Abstract
The γ-surfaces in planes (110), (120), (210), (130), and (310) containing Burgers vector [001] of a perfect dislocation in cementite were studied using the molecular dynamics method. Slip vectors corresponding to stable stacking faults (SFs) were identified, and the energy of these SFs was determined. The energy of unstable stacking faults characterizing the tendency towards plastic relaxation was estimated. It was found that local minima with low energies of both stable and unstable stacking faults are present in plane (210) of cementite. This implies the possibility of the formation of extended SFs. The possibility of splitting of a perfect dislocation with Burgers vector [001] into two partial dislocations was demonstrated.
995-1000
Mechanical and Thermomechanical Properties of the Ti50Pd40Ni10 Alloy with a High-Temperature Shape-Memory Effect Studied on a Workpiece in the Form of a Bar in the Annealed State
Abstract
Abstract—Complex studies of the properties of the Ti50Pd40Ni10 alloy (at %) with a high-temperature shape memory effect have been performed using specimens prepared from a 5.86-mm bar in the initial annealed state. Information on the temperatures of phase transformations and mechanical and thermomechanical characteristics of the alloy have been obtained. The maximum values of the shape-memory effect and of the degree of shape recovery were 1.5 and 21%, respectively. This is insufficient to create workable safety devices at this stage. The thermomechanical characteristics determined in this study are comparable with the data we obtained earlier on samples cut out from a 2.04-mm-thick strip. In spite of the rather low values of the thermomechanical characteristics obtained at the first stage of research, this alloy is a promising material, and if obtaining optimum values of working characteristics by varying manufacturing conditions and regimes of heat treatment and deformation, it can be used to create working elements of various safety devices for objects of nuclear power engineering.
1001-1005
The Microstructure and High-Strain-Rate Superplasticity of the Al–Mg–Ni–Fe–Mn–Cr–Zr Alloy
Abstract
The microstructure, superplasticity characteristics at a subsolidus temperature (540°C), and the room-temperature mechanical properties of an alloy of the Al–Mg–Ni–Fe–Mn–Cr–Zr system have been investigated using the methods of scanning and transmission electron microscopy and uniaxial tensile tests. The alloy has a bimodal particle-size distribution; it contains eutectic particles of Al9FeNi with an average size of 0.6 μm; and dispersoids with an average size of 75 nm. The particles of the secondary phases ensure grain size of approximately 4 μm after the recrystallization subsolidus annealing of the cold-rolled sheet. Due to the microsize grain structure, the alloy demonstrates a relative elongation to 500% at a subsolidus temperature in the range of the constant strain rates of 5 × 10–3 to 3 × 10–2 s–1, yield stress 215 MPa, and ultimate strength 330 MPa.
1006-1013
Mechanisms of Superplastic High-Rate Deformation in the Al–Mg–Zn–Fe–Ni–Zr–Sc Alloy
Abstract
The microstructure and acting superplastic deformation mechanisms in the high-strength Al–7.0% Zn–2.7% Mg–1.0% Ni–0.9% Fe alloy low-doped with Sc and Zr upon deformation at a temperature of 480°С and a strain rate of 1 × 10–2 s–1 at a stable flow stage in a true strain range of 1.1 to 1.6 have been investigated. To evaluate the contributions of superplastic deformation mechanisms to the total elongation, marker grids have been applied on the surface by ion etching, and microstructural changes of the surface have been analyzed. Grain boundary sliding and intragranular deformation play dominant roles. The contribution of each mechanism is 35–40%. The remaining 25% belongs to the diffusional creep mechanism, which is determined from the size of striated zones formed at the transverse grain boundaries on the surface of a deformed sample.
1014-1020
Heat Criterion of the Change of Strain-Hardening Stages in Austenitic Stainless Steel
Abstract
The infrared thermography method was used to study changes in the temperature of austenitic stainless steel in the process of tensile deformation. It was revealed that the temperature of the sample stops growing in the transition region between the linear stages of strain hardening. This phenomenon can be connected with a change in the entropy of the deformed medium as a result of a reconstruction of the ordered autowave structures. In the region of true deformation exceeding 0.4, a phenomenon of discontinuous flow (Portevin–Le Chậtelier effect) is observed, which is accompanied by the motion of the single fronts of localized deformation. The observed fronts are heat sources, and the value of the temperature at the arbitrary point of the sample is determined by its position relative to the front of deformation.
1021-1025