Α-solid Solution Research Articles

МЕТОДОЛОГИЧЕСКИЕ ОСНОВЫ МАТЕРИАЛОВЕДЧЕСКОЙ ОЦЕНКИ КАЧЕСТВА СМАЗОЧНЫХ СРЕД ДЛЯ НАГРУЖЕННЫХ СОПРЯЖЕНИЙ МАШИН И МЕХАНИЗМОВ. Сообщение 2. Влияние состава смазочных сред на структурно-фазовое состояние зоны деформации металлических трибосопряжений и их антифрикционные свойства

The results of experimental studies of deformation and diffusion in the surface layers of metallic frictional couples, which form the experimental and theoretical basis of the materials science approach to the quality evaluation of lubricants, are presented. The concepts of the component’s role for the lubricating medium in the implementation of the plasticizing and strengthening triboeffect are formulated. Structural condition characteristics for the surface layers of copper alloys during friction on steel in the mode of boundary lubrication in surface-active lubricants, are described. The conditions for achieving minimum power losses of such tribosystems for friction and wear have been found. The greatest service life of tribounit in a lubricating medium containing surfactants is resulted from wear resistance increase of a copper alloy with a relative decrease in hardness and increased plasticity of its surface layer. At the same time, a decrease in hardness due to the plasticizing effect of surfactants occurs only in the near-surface deformed layer of tribomaterial, while in its deeper layers with no plasticization resulted from a lubricating medium effect, the mechanical characteristics of the antifriction alloy remain at the required high level. It is demonstrated that alloys with a single-phase structure of an α-solid solution and a wide concentration range of solubility of the alloying element in the solid state meet these requirements. It is found that such boundary conditions are provided by the presence of stationary macroscopic diffusion flows of alloying elements in the zone of contact deformation of a polycomponent tribomaterial. The role of local diffusion phenomena in quasispinodal phase transitions is indicated. Examples of the selective transfer phenomenon during friction in industrial lubricants, are given.

Magnetization and phase transformation in Fe-Ga and Fe-Ge alloys

The magnetic properties and structural states of Fe-Ga and Fe-Ge alloys, known for their large magnetostriction, have been investigated. Experimental characterizations are supported by ab initio calculations and Monte Carlo simulations to reveal the complex interplay between magnetic properties and structural changes. Our findings are in agreement with previous investigations and show that the Curie temperature (TC) of these alloys changes gradually with increasing alloying element concentration while the A2 solid solution is being realized. Further alloying of Fe-Ga leads to the transition from a single-phase to a two-phase A2 + D03 state and results in two distinct TC values. At the same time Fe-Ge shows a more complex behavior with several phase transitions influencing the magnetic ordering temperatures. Theoretical calculations suggest a significant correlation between the magnetic moments, exchange interactions, and observed TC trends. It is shown that the D03 phase is characterized by the lowest TC among other phases. Using Monte Carlo simulations, we found that in ferromagnetic state of Fe-Ge alloy the D03 ordering develops homogeneously, while in Fe-Ga it follows a nucleation and growth scenario.

The effect of Laves phases and nano-precipitates on the electrochemical corrosion resistance of Mg-Al-Ca alloys under alkaline conditions

The electrochemical corrosion mechanisms of Mg alloys were extensively studied in previous investigations of different chemical compositions, modified surface states and various electrolyte conditions. However, recent research focused on the active state of Mg dissolution, leading to unresolved effects of secondary phases adjacent to a stable α-solid solution passive layer. The present study investigates the fundamental electrochemical corrosion mechanisms of three different Laves phases with varying phase morphologies and phase fractions in the passive state of Mg-Al-Ca alloys. The microstructure was characterized by (transmission-) electron microscopy and synchrotron-based transmission X-ray microscopy. The electrochemical corrosion resistance was determined with a standard three-electrode setup and advanced in-situ flow cell measurements. A new electrochemical activity sequence (C15>C36>α-Mg>C14) was obtained, as a result of a stable passive layer formation on the α-solid solution. Furthermore, nm-scale Mg-rich precipitates were identified within the Laves phases, which tend to inhibit the corrosion kinetics.

Структура та властивості нових підшипникових композитів на основі сталевих відходів для важких умов експлуатації друкарських машин

The article presents the research results on the structure and properties of new self-lubricating bearing composites based on grinding wastes of high-alloyed steel 8X4V2MFS2 with additives of CaF2 solid lubricant. The new composites are designed to operate in friction units of printing machines at rotational speeds of 600˗800 rpm and increased loads of up to 3.0 MPa. It is shown that the application of the developed technology ensures the formation of a fine-grained heterophase structure of the new composite. The formed structure is a metal matrix base made of regenerated grinding waste from 8X4V2MFS2 steel, consisting of a high-alloy α-solid solution and solid grains of alloying elements’ carbides, as well as a uniformly distributed solid lubricant CaF2. This structure ensured the formation of the new composite’s physical, mechanical and tribological properties high level. In the process of friction, antifriction films were formed on the contact surfaces, which provided a self-lubricating mode. Comparative friction and wear tests have shown significant advantages of the new waste composite compared to cast brass L63, which is traditionally used in friction units of printing equipment. The determined level of physical, mechanical, and tribological characteristics makes it possible to recommend the studied material for use in friction units of printing equipment operating at elevated rotational speeds of 600˗800 rpm and loads up to 3.0 MPa in air. The studies have shown the prospects of using a wide range of valuable metal grinding waste in the repeated production cycle for the manufacture of high-quality composites. The reuse of such waste will make a significant contribution to the protection of the environment from pollution associated with human industrial activity and will help reduce its negative effect on the ecosystem. Keywords: grinding waste, high-alloyed steel, technology, composite bearing, microstructure, solid lubricant, properties, antifriction films, printing machines.

Effects of quenching temperature on the structure, segregation, and properties of the AM4.5Kd + 0.2 wt.% La alloy after artificial aging

The identification of structural components in the AM4.5Kd + 0.2 wt.% La alloy, subjected to quenching at different temperatures (535–605 °C) and artificial aging at 155 °C for 4 h, was conducted through electron microscopy and XRD. An increase in the quenching temperature from 535 to 605 °C promotes the enlargement of structural components, including the α-solid solution, various aluminides, and eutectics. We observed that the base metal is not homogeneous in its chemical composition, consisting of two types of solid solutions: α1 and α2. The Cu and Mn solubility in the α2-solid solution is higher than in the α1-solid solution. As the quenching temperature increases to tq = 605 °C, the copper content in the α1-solid solution decreases. In contrast, the copper content in the α2-solid solution follows a curve with two maxima at 545 °С (4.5 at.%) and 585 °С (8.7 at.%). The Mn content in the α1-solid solution decreases sharply to the 545 °С quenching temperature and remains relatively constant up to tq = 605 °С (0.2 at.%). The Mn content in the α2-solid solution follows a curve with its maximum at tq = 545 °С (4.3 at.% Mn). Subsequent temperature rise results in a sharp drop in Mn content from 1.0 at.% at t = 565 °С to 0.3 at.% at 605 °С. Hence, the max solubility of Cu and Mn in the α2-solid solution occurs at 545 °C. At 585 °С, only an elevated Cu content (~8.7 at.%) was observed. Aluminides of alloying elements with different stoichiometries crystallize at different quenching temperatures, with complex AlxTiyLazCuvCdw and AlxCuyMnzCdv alloyed aluminides being most commonly found. ncreasing the quenching temperature to 535–545 °С results in higher hardness of the AM4.5Kd + 0.2 wt.% of La alloy, reaching 98–104 HB, with subsequent decrease to 60 HB as the quenching temperature reaches 605 °С. The hardness of the unhardened alloy is 60 HB. The optimal quenching temperature for the AM4.5Kd + 0.2 wt.% of La alloy is in the range of 535–545 °С. This temperature corresponds to the highest hardness of the alloy and the microhardness of the aluminide.

On the Microstructure and Properties of Complex Concentrated bcc Solid Solution and Tetragonal D8m M5Si3 Silicide Phases in a Refractory Complex Concentrated Alloy

In this work, the refractory complex concentrated alloy (RCCA) 3.5Al–4Cr–6Ge–1Hf–5Mo–36Nb–22Si–1.5Sn–20Ti–1W (at.%) was studied in the as cast and heat treated conditions (100 h or 200 h at 1500 °C). There was strong macrosegregation of Si in the 0.6 kg button/ingot of the cast alloy, in which A2 solid solution, D8m βNb5Si3, C14-NbCr2 Laves phase and Tiss and a ternary eutectic of the A2, D8m and C14 phases were formed. The partitioning of Ti in the as cast and heat treated microstructure and its relationships with other solutes was shown to be important for the properties of the A2 solid solution and the D8m βNb5Si3, which were the stable phases at 1500 °C. The near surface microstructure of the alloy was contaminated with oxygen after heat treatment under flowing Ar. For the aforementioned phases, it was shown, for the first time, that there are relationships between solutes, between solutes and the parameters VEC, Δχ and δ, between the said parameters, and between parameters and phase properties. For the contaminated with oxygen solid solution and silicide, trends in relationships between solutes, between solutes and oxygen content and between the aforementioned parameters and oxygen content also were shown for the first time. The nano-hardness and Young’s modulus of the A2 solid solution and the D8m βNb5Si3 of the as cast and heat-treated alloy were measured using nanoindentation. Changes of nano-hardness and Young’s modulus of the A2 solid solution and D8m βNb5Si3 per solute addition for this multiphase RCCA were discussed. The nano-hardness and Young’s modulus of the solid solution and the βNb5Si3, respectively, were 9.5 ± 0.2 GPa and 177.4 ± 5.5 GPa, and 17.55 ± 0.5 GPa and 250.27 ± 6.3 GPa after 200 h at 1500 °C. The aforementioned relationships and properties of the two phases demonstrated the importance of synergy and entanglement of solutes, parameters and phases in the microstructure and properties of the RCCA. Implications of synergy and entanglement for the design of metallic ultra-high temperature materials were emphasised.

Effect of Pressure and Gravitational Field on the Distribution of Cu during the Directed Growth of a Single Crystal of the Alloy Al–0.005 wt % Cu

Abstract—Using quantitative X-ray spectral analysis and metallography, the distribution of copper concentration in the α-solid solution of Al and the dislocation density in single crystals of the Al alloy–0.005 wt % Cu, grown from the melt at different values of argon pressure (Ar) and the gravitational field component (gmg) directed along the surface of the crystallization front. A strong inhomogeneity in the copper concentration measured in adjacent areas of the cross-sectional surface of the crystal and its correlation with the inhomogeneity of the distribution of dislocations in single crystals of the alloy, which depends on pressure and the gravitational field component, were discovered. The mechanism of relaxation of the excess free volume of the phase transformation released in the region of the interphase boundary during crystal growth is considered.

INVESTIGATION OF PHASE EQUILIBRIA AND PHYSICO-CHEMICAL PROPERTIES OF OBTAINED PHASES IN THE Sb2S3-Cr2Se3 SYSTEM

Using complex of physicochemical methods of analysis (DTA, XRD, MSA, as well as measurements of density and microhardness), the phase equilibria in the Sb2S3-Cr2Se3 system was studied and a phase diagram was constructed. It is established that the system is quasi-binary and has eutectic type T-x diagram. In the process of chemical interaction, a compound with composition Cr2Sb2S3Se3 is formed in the system. The Cr2Sb2S3Se3 compound melts incongruently at 6500C., A limited area of the solid solution based on the initial components of the system is formed. The coordinates of the eutectic formed between the α-solid solution and the Cr2Sb2S3Se3 compound is 17 mol % Cr2Se3 at 4500C. At room temperature, solid solutions based on Sb2S3 reach up to 5 mol % Cr2Se3, and based on Cr2Se3 up to – 3 mol % Sb2S3. According to the results of X-ray diffraction analysis, Cr2Sb2S3Se3 crystallizes in a tetragonal system with lattice parameters: a=16.37; c=11.69 Å, ρpuc.=5.40 q/sm3, ρX-ray=5.42 q/sm3. The temperature dependence of the electrical conductivity and thermo-EMF of the (Sb2S3)1-x(Cr2Se3)x (x=0.01; 0.02; 0.03;) solid solution has been studied

Liquid matrix SHS manufacturing and heat treatment of Al–Mg composites reinforced with fine titanium carbide

Aluminum matrix composites reinforced with ultra-fine refractory titanium carbide feature a unique combination of properties. They are promising structural materials. Self-propagating high-temperature synthesis (SHS) is an affordable and energy-saving composite making process. It involves the exothermic reaction between titanium and carbon (or their compounds) directly in the melt. We studied the properties of SHS composites based on the AMg2 and AMg6 commercially available alloys reinforced with 10 wt.%TiC. We investigated the macroand microstructure of the samples with XRD and EDS analysis. It was found that the β-phase is separated from α-solid solution of aluminum as early as the air cooling stage. We conducted experiments aimed at studying the effects of additional heating on the sample structure and properties and found the optimal temperature and time values. We also proposed a phenomenological model of the structural transformation sequence. We compared the physical, mechanical, and manufacturing properties and corrosion resistance of the original cold-hardened AMg2N and AMg6N alloys and the composites before and after heat treatment. It was found that additional heating reduces porosity and maintains electrical conductivity. It was also found that the compressive strength and relative strain of the composite based on the AMg2 alloy change insignificantly, while for the AMg6-based composite the reduction is more significant. Heat treatment increases the composite hardness while maintaining sufficient plastic deformation. It is confirmed by the measured values of the relative strain and the reduction ratio close to that of the original matrix alloys. It was also found that the composites retain high resistance to carbon dioxide and hydrogen sulfide corrosion.

Структура и свойства низкоуглеродистой стали после плазменной наплавки борсодержащей обмазки

Introduction. One of the effective thermochemical methods for increasing the hardness of steel is boronizing by diffusion of boron atoms into the steel surface at high temperatures. As a result of boronizing, coatings are formed on the steel surface, consisting of columnar crystals of FeB and Fe2B. The volume fraction of phases and the thickness of the coatings depend on the heating temperature and the chemical composition of the base material and the saturating medium. The main disadvantage of these boronized layers is its high brittleness. Boronizing by plasma heating is one of the alternatives to the diffusion boronizing process to minimize the brittleness of the boronized layer. The purpose of the work: to form boride coatings on low-carbon steel using plasma-jet hard-facing. The research methods are: determination of the content of chemical elements using an electron probe micro-analyzer, metallographic studies, analysis of the phase composition of the boronized layer, as well as measurement of the microhardness of the coating after plasma-jet hard-facing. In this work boronized layers obtained on low-carbon steel 20 by plasma-jet hard-facing of a boron-containing coating are studied. Powdered amorphous boron was used as an alloying element. The parameter varied during plasma-jet hard-facing process is the current strength (120 A, 140 A and 160 A). Results and discussions. Based on the studies performed, it is found that it is possible to form boronized layers on the steel surface using plasma-jet hard-facing method. It is noted that the surface layer of the coating of the 1st and 2nd specimens after plasma-jet hard-facing has a heterogeneous structure, consisting of rows of different zones. The first zone has a hypereutectic structure, which consists of primary borides FeB and Fe2B, located in the eutectic, consisting of Fe2B and α-Fe. The second zone above the boundary with the base metal is represented by eutectic colonies composed of Fe2B and α-Fe. The third specimen is characterized by a hypoeutectic structure consisting of boride eutectic and primary dendrites of the α-solid solution of boron in iron. The maximum hardness is fixed on the surface of the first specimen and is 1,575 HV. The depth of the hardened layer increases with increasing current, but the hardness value and boron content decrease after treatment. The slight hardness gradient observed over the depth of the coating, as well as the gradual decrease in hardness due to the presence of the transition zone, are considered favorable for good adhesion of the boronized layer to the surface of the base material.

Ga-SrSe SİSTEMİNDӘ KİMYӘVİ QARŞILIQLI TӘSİRİN TӘDQİQİ

Using methods of physicochemical analysis: differential thermal analysis (DTA), X-ray phase analysis (XPA), microstructural analysis (MSA), as well as determination of microhardness and density, the chemical interaction in the Ga-SrSe system was studied and a T-x phase diagram was constructed. It has been established that the Ga-SrSe system is quasi-binary and degenerate of the eutectic type. It has been established that at room temperature in the system Ga-SrSe a solid solution based on SrSe up to 5 mol % Ga. One of the methods for physicochemical analysis of semiconductor compounds is to determine their microhardness depending on the composition. In the Ga-SrSe system, two different microhardness values are defined. One of them is the microhardness of SrSe (1240-1250) MPa, the value of which corresponds to the microhardness of an α-solid solution based on the SrSe compound, and the microhardness value (700- 730) MPa corresponds to the microhardness of gallium.. The densities obtained in the system increase monotonically depending on the composition.

STABILITY OF THIN QUASI-CRYSTALLINE Ti-Zr-Ni FILMS AND RELATED CRYSTALLINE PHASES UNDER LOW-ENERGY TRANSIENT PLASMA IRRADIATION

The properties of Ti41Zr38.3Ni20.7 thin films under radiation-thermal action of hydrogen plasma with a surface heat load of 0.2 MJ/m2 was studied at the QSPA Kh-50 quasi-stationary plasma accelerator (NSC KIPT).The phase composition, structural state, and surface morphology were studied using X-ray diffraction and scanning electron microscopy. It was found that the quasicrystalline phase and related crystalline phases, the Laves phase, the α-solid solution, and the 2/1 phase of the Ti-Zr-Ni approximant crystal were stable under irradiation with up to 20 hydrogen plasma pulses. The phase composition did not change. It is shown that the changes in the coatings mainly manifest themselves as changes in the substructure of the observed phases. With an increase in the plasma exposure dose, the structure of the quasicrystalline icosahedral phase improves, and the size of the coherence regions increases. In the films consisting of crystalline phases, a partial phase transformation is observed with a redistribution of components between the 2/1 phase of the approximant crystal and the α-solid solution phase. It was found that thin films of the TiZr-Ni system containing a quasicrystalline icosahedral phase, irradiated with radiation-thermal plasma pulses, are less prone to cracking than coatings with crystalline phases of the same system.

Phase transitions and mechanical behavior of Ti-3wt.%Nb alloy after high pressure torsion and low-temperature annealing

The influence of microstructure and phase transitions on tensile strength, plasticity and microhardness of a Ti-3wt.%Nb alloy subjected to high pressure torsion (HPT) followed by annealing is studied in this work. The initial state of the alloy was the α-solid solution with a small amount of the β-precipitates. The characterization of microstructure and phase transitions has been performed using scanning and transmission electron microscopy as well as X-ray diffraction. During HPT, the grain refinement took place and the α-phase partially transformed into ω-phase. The tensile test of the HPT-deformed sample showed an almost two-fold increase of ultimate strength in comparison with the initial state, as well as lower plasticity. During the short-term annealing of the deformed state up to 250 °C, the grain size slightly increased, the density of the crystal structure defects decreased and ω-phase transformed back to the α-phase. Such microstructural changes led to an important growth of plasticity and a slight decrease in ultimate strength of the HPT-deformed alloy.

Enhanced viscous glide creep in disordered β (Cu17Sn13) intermetallic phase with coarse grains

High-temperature deformation mechanisms and processing maps of the coarse-grained A2 (disordered BCC) β (Cu17Sn13) intermetallic phase alloy (with the chemical composition of Cu-24.6 wt %Sn) were examined in compression in the temperature range of 843–993 K and strain rate range of 10−3-10 s−1. The β phase exhibited a stress exponent (n1) of nearly 3 over almost the entire strain-rate range at these temperatures. Limited subgrain formation occurred during hot compression. This microstructural feature and the observation of n1 = 3 strongly suggest that solute drag creep is the main high-temperature deformation mechanism. A comparison of the high-temperature deformation mechanisms and behaviors of the BCC β phase and FCC α-solid solution phase (with the composition of Cu–10Sn alloy studied in previous work) shows that both β and α phases exhibit solute drag creep, but β is considerably weaker in strength, and the upper limit of strain rate for solute drag creep is much higher (over 100 times). Solute drag creep at high strain rates in the β phase can be attributed to the high breakaway stresses for dislocations from the solute atmosphere in the presence of a high concentration of Sn solutes in the matrix. The β phase exhibits superior hot workability compared with the α phase according to the processing maps, especially at high strain rates. This is because there is no flow instability regime for the β phase under the investigated testing conditions and the power dissipation efficiency at high strain rates is higher in the β phase compared with the α phase.

Influence of parameters used for melt processing by nanosecond electromagnetic pulses on the structure formation of cast aluminum matrix composites

The paper focuses on establishing the effect of nanosecond electromagnetic pulses (NEPs) with different amplitudes on the formation of the structure of cast aluminum matrix composites of the Al–Mg2Si pseudobinary system with hypoeutectic (5 wt. % Mg2Si) and hypereutectic (15 wt. % Mg2Si) compositions. As the NEP generator amplitude in composites containing 5 and 15 wt. % Mg2Si increases, the matrix alloy structural components (α-solid solution and eutectic) are refined, while no significant differences in the sizes and morphology of Mg2Si primary crystals were observed in the hypereutectic range of compositions. Presumably, the observed nature of the NEP effect on the structure of composites in the hypereutectic region of compositions is associated with the features of their crystallization behavior. The temperature range of the L + Mg2Si two-phase region presence is much lower than NEP irradiation temperatures. Apparently, this is the reason why NEPs have no effect on the thermodynamic state of Mg2Si primary crystal/melt interfaces. It was shown that a promising option for the simultaneous modifying effect on all structural components of Al–Mg2Si aluminum matrix composites (solid solution, eutectic, Mg2Si primary particles) is a combination of thermal-rate treatment and irradiation of melts by NEPs, as well as additional melt processing by NEPs during crystallization.

Вплив МГД - плазмової обробки розплаву на структуру і властивості литого алюмінієвого сплаву А390

Growth of production of cast products and the desire of enterprises to reduce the cost of manufacturing metal products led to a significant increase in requirements for the structure and properties of aluminum alloys. Increasing of physical and mechanical properties of alloys is most effectively at the stages of their preparation in liquid state. At that, it is possible to affect effectively on the quality of cast metal by external actions on alloys, deep refining from gases and harmful impurities, active modifying of alloy, reducing or eliminating the negative impact of heredity of charge materials. The main disadvantage of the processes of structure refinement of alloys by using modifiers is instability of their results, which depends on various reasons. One of the most important reasons is providing conditions for the formation and preservation of active modifier particles in the melt volume. They are assimilating by liquid alloy and acting on crystal nucleus at crystallization. It is known that only ~10% particles are active of the total number of particles added with the ligature into the melt. Other particles dissolve in the melt, take away by the crystallization front, or push back on to intergranular boundaries. The considered methods of electromagnetic, MHD and plasma actions on liquid metal allow to refine and modify alloys without use of special reagents. The paper presents studying of the structure and properties of supereutectic silumin A390 after treatment in casting magnetodynamic installation (MDI) by submerged into melt the plasma argon jet and alternating electromagnetic field & magnetohydrodynamic (MHD) effects, including simultaneous combination. There are developed the scientific and technological bases of MHD-plasma processing of liquid hypereutectic silumin A390 and original equipment for their realization. It provides dispersed structure of solidified alloy. Thus, there is a significant decreasing of sizes both particles of primary silicon and dendrites of α-solid solution of aluminium. Also, strength characteristics of alloys increased to 10%, and elongation rises up in 1.5-2 times. Keywords: plasma jet, magnetodynamic installation (MDI), aluminum alloy, mechanical properties.

Structural-and-Phase Transformations in Fe-4.10 and 7.25 at.% Mn Alloys under Intensity External Actions

The effect of high-pressure torsion (HPT) (P = 8 GPa, e = 5.9) and irradiation with continuous beams of Ar+ ions with energy E = 15 keV on the atomic structure and phase composition of initially quenched iron alloys with 4.10 and 7.25 at.% Mn was studied by the method of Mössbauer spectroscopy. The supersaturated α-solid solution of Fe-7.25 at.% Mn, in contrast to the stable Fe-4.10 at.% Mn, which passes into a highly nonequilibrium metastable state as a result of HPT deformation, is transformed under the influence of ion irradiation at an abnormally low temperature of 280 °C into a two-phase α + γ-state with a highly enriched γ-phase (austenite) (38.4 at.% Mn) and a depleted α-solid solution with 5.76 at.% Mn. The rapid processes with the formation of the γ-phase with a concentration of Mn close to the extrapolation estimate using the equilibrium phase diagram are explained by the cascade radiation shaking of the material by post-cascade powerful elastic and shock waves. Cascade radiation shaking plays the role of temperature and opens up the possibility of achieving states close to equilibrium in the absence of thermally activated processes at record low temperatures.

Відпускна крихкість литої штампової сталі 4Х4Н5М4Ф2

The results of research of structural steel brand 4Kh4N5М4F2 after heat treatment are given. Manifestations of tempering brittleness at a temperature of 450-500 °C, associated with the maximum value of the parameter «a» of the crystal structure during the formation of a solid substitution solution in the system "Fe-C". The connection between the peculiarities of the crystal structure of the studied steel and the complex of physical and mechanical properties is established. The maximum value of the parameter «а» (a = 0.28848 nm) of the elementary cell of martensite crystal lattice reflects the maximum saturation of the α-solid solution, which increases the resistance of the crystal lattice to deformation, increase the hardness of tempering martensite (up to 56 HRC), change the physical structure sensitive value (increase in specific conductivity to 0,200 Om•mm2/m), increase the tensile strength, reduce the impact strength (up to 15 J/cm2) and increase the brittleness at temperatures of 450-500 °C. The possibility of using matrices (steel 4Kh4N5М4F2, without forging technology) for hot deformation of aluminum alloy AK7ch, which during operation does not reach the temperature of brittleness (above 460 ºC), is demonstrated. Keywords: die steel, crystal structure, heat treatment, physical and mechanical properties.

The Phase Transformations Induced by High-Pressure Torsion in Ti–Nb-Based Alloys

The study of the fundamentals of the α → ω and β → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Prior to HPT, three alloys with 5, 10, and 20 wt% of Nb were annealed in the temperature range of 700–540°C in order to obtain the (α + β)-phase state with a different amount of the β-phase. The samples were annealed for a long time in order to reach equilibrium Nb content in the α-solid solution. Scanning electron microscope (SEM), transmission electron microscopy, and X-ray diffraction techniques were used for the characterization of the microstructure evolution and phase transformations. HPT results in a strong grain refinement of the microstructure, a partial transformation of the α-phase into the ω-phase, and a complete β → ω phase transformation. Two kinds of the ω-phase with different chemical compositions were observed after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the almost Nb-pure α-phase. It was found that the α → ω phase transformation depends on the Nb content in the initial α-Ti phase. The less the amount of Nb in the α-phase, the more the amount of the α-phase is transformed into the ω-phase.

Structure evolution of as-cast metastable Fe-38Ga alloy towards equilibrium

The evolution of the structural phases of the Fe-38.4 at%Ga alloy was studied in neutron diffraction experiments performed with high-intensity continuous scanning in a wide temperature range. The as-cast alloy consists of ~70% Fe13Ga9 intermetallic and ~30% bcc-based disordered A2 solid solution (or its partially ordered/short-range ordered B2 variant). The research proves that during the first heating of the cast alloy, the Fe13Ga9 phase is stable up to T ≈ 550 °C, then it transforms into α-Fe6Ga5, fcc-based L12 and B2 phases. At the same temperature, the disorder-order transition A2 → B2 begins, ending at T ≈ 720 °C. The Fe13Ga9 phase does not restore during subsequent cooling and next heating and cooling cycles. The structural parameters of the identified phases are refined. The research also shows that the transition temperatures depend on the alloy prehistory.