Papers by Keyword: Phase Composition

Abstract: Phase components of experimental low cost titanium alloys, their substructure and parameters, dislocation structure, features of phase formation in the metal, which differ in alloying systems, were studied using complex research methods. The stoichiometric composition of dispersed phases in the internal volumes of alloy grains was determined by diffraction patterns using transmission electron microscopy. It is shown that in the structure of titanium alloy Ti-2,8Al-5,1Mo-4,9Fe there are dispersed nanoparticles of intermetallic phases of different morphology and stoichiometric composition. These are the phases: Ti₃Al and Fe₂Ti with a size of 10…40 nm; Mo₉Ti₄ - 20…120 nm. Studies of titanium alloy Ti-1,5Fe-O showed the presence in the structure of mainly nanoparticles of oxides: Ti₃O₅ size 10…30 nm and Ti₄Fe₂O, FeTiO₅ (10…90 nm), as well as intermetallics Fe₂Ti (10…40 nm). It is established that the formation of nanoparticles of intermetallic and oxide phases in the thin plate structure of the investigated experimental low cost titanium alloys promotes the formation of the substructure with uniform distribution of dislocation density. This provides a high level of mechanical properties of alloys.

Abstract: A FeCoNiCu high-entropy alloy was synthesized via mechanical alloying using elemental powders. The structural evolution during milling and the effects of subsequent sintering were investigated. X-ray diffraction confirmed the formation of a single-phase FCC solid solution with nanocrystalline structure. SEM and EDS analyses showed homogeneous element distribution without segregation. Microhardness testing revealed an average value of 105.47 HV1, indicating sufficient mechanical performance. The results demonstrate the potential of FeCoNiCu HEAs for structural applications.

Abstract: Increasing the operational reliability and durability of parts and mechanisms used to operate under conditions of intense wear, loads, high pressure and temperatures requires the protection of working surfaces with functional coatings. The E.O. Paton Institute of Electric Welding of the National Academy of Sciences of Ukraine has developed a technology and equipment for multichamber detonation spraying (MCDS) of these coatings. This paper summarizes the data of experimental studies of the structure of composite coatings of various systems (Ni–Cr–Fe–B–Si, Cr₃C₂–NiCr, WC–Co–Cr, ZrSiO₄, and Al₂O₃) for different materials. Research has established the influence of technological modes of spraying on structural and phase changes in the coating materials obtained by detonation spraying. Under different processing modes, the materials change volume fraction of phase components, microhardness, (sub)grain structure parameters, size of dispersed phases, and nature and distribution of dislocation density. The peculiarity of the structure of coatings obtained by the MCDS method is the formation of a dispersed structure, the presence of a nanoscale substructure and nanoparticles of hardening phases with a size of 10–100 nm. The formation of a nanostructural state contributes to an increase in the strength, fracture toughness, and crack resistance of coatings obtained by the MCDS method.

Abstract: The paper presents the results of an investigation into the reduction processes of iron ore titanomagnetite pellets using synthesis gas. The thermodynamic modelling was carried out using the TERRA software package. Synthesis gas is a mixture of carbon monoxide (CO) and hydrogen (H₂), as well as other gases such as CO₂ and N₂. It is primarily used in the production of liquid fuels and chemical products, and is produced through the initial conversion of natural gas and coal fuel. The TERRA software package was used to model and predict chemical and phase transformations in pellets during reduction. The model takes into account the influence of temperature, hydrogen concentration, and other parameters on the reduction kinetics. Calculations were carried out with different gas mixtures and conditions to evaluate the model's effectiveness. The thermodynamic model constructed corresponds to the literature and calculated data and can be used to optimize the reduction process under various production conditions.

Abstract: The structure and mechanical properties of a multicomponent high-entropy Al₄CoCrCuFeNi alloy in the as-cast and melt-quenched states were investigated. The alloy composition was analyzed based on the literature criteria for predicting the phase formation in high-entropy alloys, which considered the entropy and enthalpy of mixing, valence electron concentration as well as the atomic size difference of the components. The alloy films were synthesized by quenching from the melt using a splat-quenching technique. The cooling rate of the films was estimated to be ~ 10⁶ K/s based on the film thickness. The X-ray diffraction analysis revealed that both as-cast and melt-quenched Al₄CoCrCuFeNi alloy samples had an ordered B2 phase in their structure. The microhardness of the as-cast alloy was 6500 MPa, while the microhardness of the melt-quenched film was significantly higher and reached 9400 MPa.

Abstract: The initial and final softening (melting) temperatures of redesigned iron ore agglomerates with basicities from 1.2 to 3.0, obtained under laboratory conditions, were investigated. The chemical and phase compositions of the laboratory agglomerates, their microstructures and local chemical compositions, the temperatures at the beginning and end of softening (melting), and the temperature interval of softening were studied. Dependencies of the influence of the basicity of iron ore agglomerates on their softening temperature interval, depending on the proportion of phase components, were obtained. It is shown that as the basicity and proportion of silicoferrite SFCA phases increase, the temperatures at the beginning and end of the softening increase and reach a maximum of 1200 and 1312 °С, respectively (at the basicity of the agglomerate of 1.8), after which the temperatures decrease. Simultaneously, the softening interval increased from 73 to 112 °C.

Abstract: In the course of the study, several different methods of surface structural engineering are reviewed. The methods described in this paper are characterized by different process physics on the way to obtaining the result, but they are aimed at modifying the structure and properties of the surfaces to which they are applied. Among them, two different technological directions are considered. The first area involves technologies that include a friction component, namely thermofriction treatment (TFT) for thermofriction strengthening (TFS), additional thermofriction strengthening (ATFS) or thermofriction welding (TFW). The second direction is a technology that involves the use of an anode-cathode electrolysis mode in an alkaline-silicate electrolyte – micro-arc oxidation (MAO). The paper describes the features and results of the application of such technologies and the feasibility of using this or that method for materials of different classes, and presents schemes of the corresponding installations. The result of additional hardening of the surface of U8A steel from a microhardness level of 7.2 GPa to 14.7 GPa using the ATFS method after its thermal hardening to almost the maximum possible level is shown. The microstructure of the cross-section of a prehardened specimen of U8A steel after ATFS is presented, where the degree and nature of surface hardening are reliably visible. It is emphasized that in previous studies, consistently effective hardening of steels of various classes has been achieved, even up to the level of 22 GPa in 65G steel. Regarding the method of microarc oxidation, the structure and properties of coatings on low-alloy aluminum alloys AB and AD1 formed in an alkaline-silicate electrolyte in the anode-cathode MAO mode were investigated. It is shown that the method of MAO in alkaline-silicate electrolyte allows to obtain a coating thickness of up to 300 μm, a coating growth rate of ~ 2 μm/min, and a coating hardness of 10-20 GPa. The coatings have high adhesion to the substrate; they have a layered structure. The properties of the coatings are determined by the properties of the base layer. The coatings have a crystalline structure and consist of the following phases: γ-Al₂O₃, α-Al₂O₃, mullite (3Al₂O₃·2SіO₂), the ratio between the phases depends on the electrolysis conditions. It has been established that phase formation begins with the γ-Al₂O₃ phase, which in the process of further coating growth turns into the α-Al₂O₃ phase or interacts with silicon oxide to form the mullite phase.

Abstract: Strength characteristics of iron ore agglomerates of various basicity (mechanical strength and abrasion resistance, thermomechanical strength) have been investigated. The chemical and phase compositions of iron ore agglomerates, their microstructure and local chemical composition were analyzed. Dependences of the strength characteristics of iron ore agglomerates of various basicity on the morphology of silicate bond have been obtained. Dependences of influence of basicity of iron ore agglomerates on their strength characteristics depending on the proportion of phase components are obtained. It has been shown that an increase in the proportion of stabilized silicoferrite (SFCA) in the composition of agglomerates has a positive effect on their thermomechanical strength, which will increase the productivity of the blast furnace and significantly reduce the emission of dust.

Abstract: In order to reveal the carbonation mechanism of alkali-activated concrete, the accelerated carbonation tests based on alkali-activated slag pastes were carried out. The evolution of microstructure and chemical composition for alkali-activated slag pastes subjected to carbonation was analyzed combining thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP) and a recently developed extended X-ray attenuation method (XRAM). The results showed that, the microstructure of alkali-activated slag pastes deteriorated gradually. Based on MIP and XRAM, the porosity of S4 (sample with a water-binder ratio of 0.4) increased by 8.24% and 11% after carbonation, and that of S6 (sample with a water-binder ratio of 0.6) increased by 7.45% and 10%, respectively. Besides, thermal analysis showed that, after carbonation, 11.45 mol / L and 19.57 mol /L CaCO₃ were produced separately by S4 and S6. The main carbonation product for S6 was calcite, but for S4 vaterite and disorderly stacked calcite were also presented.

Abstract: Four various methods of powder feedstock preparation for laser powder bed fusion are compared. Application of commercial spherical powder leads to the formation of single-phased state. Powder mechanically alloyed during 14 minutes in air atmosphere provides conditions for the formation of double-phased state with nonuniform distribution of components in the samples. Mechanical alloying in Ar-atmosphere during 30 minutes leads to the formation of double-phased state with more uniform distribution of components and precipitations of Cr₂O₃. Preliminary mechanical sieving of the powder allows to produce double-phased samples with nonuniform distribution of components comparable with that in samples produced from powder mechanically alloyed during 14 minutes in air atmosphere. Microhardness of all the studied samples produced from all the studied powders was comparable. All the proposed methods of powder feedstock preparation are applicable in laser powder bed fusion depending on the required properties, elemental and phase composition of the final product.