Interstitial Cr Impurities in Iron: Multiferroic Properties

Using the density functional theory, we perform a full atomic relaxation of the bulk ferrite with 12.5%-concentration of monoatomic interstitial Cr, which is periodically located at the edges of the Feα b.c.c. cell. As shown, structural relaxation leads to significant atomic displacements and results in the formation of novel high-stable magnetoelastic configurations with parallel chains of octahedrically arranged Fe. The enhanced magnetic polarization in the low-symmetry metallic state of such alloys can be externally controlled by additional introduction of nonmagnetic impurities like nitrogen. The electronic properties of obtained interstitial alloys can have important consequences for the applications in spintronic and multifunctional devices.З використанням теорії функціоналу густини виконано повну атомову релаксацію об’ємного фериту з 12,5%-концентрацією моноатомового міжвузловинного Cr, який періодично розташовується на гранях ОЦК-комірки Feα. Показано, що структурна релаксація призводить до значних зміщень атомів і формування нових високостабільних конфіґурацій з паралельними ланцюжками октаедрично впорядкованого Fe. Збільшена магнетна поляризація в низькосиметрійному металевому стані цього типу стопів може контролюватися ззовні додатковим введенням немагнетних домішок, таких як азот. Електронні властивості одержаних стопів втілення можуть виявитися важливими для їх застосування в спінтроніці та багатофункціональних приладах.С использованием теории функционала плотности произведена полная атомная релаксация объёмного феррита с 12,5%-концентрацией моноатомного междоузельного Cr, который периодически располагается на гранях ОЦК-ячейки Feα. Показано, что структурная релаксация приводит к значительным смещениям атомов и формированию новых высокостабильных конфигураций с параллельными цепочками октаэдрически упорядоченного Fe. Увеличенная магнитная поляризация в низкосимметрийном металлическом состоянии этого типа сплавов может контролироваться извне дополнительным внедрением немагнитных примесей, таких как азот. Электронные свойства полученных сплавов внедрения могут оказаться важными для их применения в спинтронике и многофункциональных приборах

Interstitial Fe-Cr alloys: Tuning of magnetism by nanoscale structural control and by implantation of nonmagnetic atoms

Using the density functional theory, we perform a full atomic relaxation of the bulk ferrite with 12.5%-concentration of monoatomic interstitial Cr periodically located at the edges of the bcc Fe$_\alpha$ cell. We show that structural relaxation in such artificially engineered alloys leads to significant atomic displacements and results in the formation of novel highly stable configurations with parallel chains of octahedrically arranged Fe. The enhanced magnetic polarization in the low-symmetry metallic state of this type of alloys can be externally controlled by additional inclusion of nonmagnetic impurities like nitrogen. We discuss possible applications of generated interstitial alloys in spintronic devices and propose to consider them as a basis of novel durable types of stainless steels.Comment: 8 pages, 10 figure

Investigation of the microstructure and properties of TRIP 800 steel subjected to low-cycle fatigue

The present work describes in detail the heterogeneousmicrostructure evolution of a high-strength steel (TRIP 800 steel) at the low-cycle fatigue conditions. Based on the extended investigations (via the optical and electron microscopy, the electron backscattering diffraction), we propose suggestions on the influence of phase composition on the mechanical properties and the crack-initiation processes. The preferential places of the crack nucleation caused by fatigue are detected, and the completeness of phase transformation via the induced plasticity is evaluated.Дана робота детально описує гетерогенну еволюцію мікроструктури високоміцної криці (TRIP 800) за умов малоциклової втоми. На підставі розширених досліджень (оптичною й електронною мікроскопією, дифракцією зворотнього розсіяння електронів) запропоновано рекомендації щодо впливу фазового складу на механічні властивості та процеси зародження тріщин. Виявлено осередки переважного зародження тріщини, спричинені втомою, й оцінено повноту фазового перетворення за рахунок індукованої пластичності.Данная работа подробно описывает гетерогенную эволюцию микроструктуры высокопрочной стали (TRIP 800) в условиях малоцикловой усталости. На основании расширенных исследований (оптической и электронной микроскопией, дифракцией обратного рассеяния электронов) предложены рекомендации относительно влияния фазового состава на механические свойства и процессы зарождения трещин. Обнаружены очаги предпочтительного зарождения трещины, что вызвано усталостью, и оценена полнота фазового превращения за счёт индуцированной пластичности

Structure peculiarities and properties of magnesium oxide layers formed by a hybrid ion-plasma discharge system

The structure and properties of magnesium oxide layers formed by a hybrid ion-plasma discharge system were investigated. The layers consist of the MgO phase which possesses a high degree of polycrystallinity. Grains are formed by the island mechanism with their subsequent joining in clusters. The dielectric layers of magnesium oxide are uniformly distributed over the substrate surface. The average values of grains diameter and surface roughness that are 82.353 and 35.628 nm, respectively, were found

Determination of properties of non-spherical VT20 alloy powders for modelling packing density

The study of unfavorable titanium alloy powders of VT20 grades was carried out and the methods of computer analysis were applied to determine the parameters of their optimal packaging. Metallographic studies were performed on a scanning electron microscope EVO-40XVP, and elemental analysis was performed using an energy dispersion spectrometer OXFORD INCA Energy 350. Determination of particle size distribution of powders was performed using image analysis software ImageJ. The surface morphology of non-spherical particles of VT20 alloy powder was studied for three different fractions: 100 ... 160 μm, 160 ... 200 μm and 200 ... 250 μm. It is shown that the powder particles are characterized by a nonspherical shape and a small difference in size. There is a tendency according to which when the particle size of the powder of the investigated alloy decreases, their shape approaches spherical. According to the results of particle size analysis, it was found that the usual sieve analysis does not allow to fully assess the distribution of powder by fractions. It was found that for the fraction 200 ... 250 μm the dominant particles are with an average diameter of 226 μm, for the fraction 160 ... 200 μm - 177 μm and for the fraction 100 ... 160 μm - 114 μm, respectively. Thus, for the fraction of titanium powder of the BT20 brand 200 ... 250 the polydispersity is 6.4%, for the fraction 160 ... 200 - 8.3%, and for the fraction 100 ... 160 - 9.1%. It is established that the fluidity of titanium alloy powders of the BT20 brand is: for the fraction 200 ... 250 μm - 62.35 s, for the fraction 160 ... 200 μm - 65.44 s, and for the fraction 100 ... 160 - 68, 73 s. That is, the highest value of fluidity is characterized by the powder with the largest particle size. Simulation of the pre-defined volume filling was performed using the "Spheres test" program. The average radii of particles of VT20 titanium alloy powder particles and the probability of the sizes of each of fractions of powder which is necessary at filling of the set volume was calculatedthe possibility of their precipitation have been established. Based on the obtained results, the packing density of VT20 titanium alloy powders was calculated depending on their fractional composition. It is confirmed that as the particle size of the powder decreases, their packing density increases. The surface morphology of non-spherical particles of VT20 alloy powder of different fractional composition and their particle size characteristics were studied. It is shown that with decreasing fractional composition of powder fractions, their homogeneity and bulk density increase. It was found that finer fractions are characterized by poorer fluidity. The simulation results determine the optimal fractional composition of the powder to fill the pre-specified volume. It is shown that as the size of the test particles decreases, their packing density increases

The effect of water vapor containing hydrogenous atmospheres on the micro-structure and tendency to brittle fracture of anode materials of YSZ–NiO(Ni) system

Purpose: The purpose of this work is to estimate the tendency to brittle fracture of the YSZ–NiO(Ni) anode cermet in a hydrogenous environment with various concentrations of water vapor. Design/methodology/approach: YSZ–NiO ceramic plates were fabricated by sintering in an argon atmosphere. The treatment of material was performed in a hydrogenous environment with various concentrations of water vapor. The strength test was performed under three-point bending at 20°C in air. The microstructure and morphology of the fracture surface of the specimens were studied using a scanning electron microscope (SEM) Carl Zeiss EVO-40XVP. The chemical composition was determined using an INCA ENERGY 350 spectrometer. Microhardness measurements were performed on a NOVOTEST TC-MKB1 microhardness tester. The configuration of the imprints and cracks formed was studied on an optical microscope Neophot-21. The porosity of the materials was investigated by analysing the SEM micrographs using the image processing technique. Findings: Peculiarities of changes in the microstructure, the morphology of specimens fracture surface, physical and mechanical characteristics of YSZ–NiO(Ni) material for solid oxide fuel cell (SOFC) anodes of different preconditioning modes aged under various partial pressures of water vapor in a hydrogenous environment are found. Research limitations/implications: To study the actual behaviour of the YSZ–NiO(Ni) anode material in the operating environment, it is necessary to evaluate its strength, Young’s modulus, microhardness, and fracture toughness by changing with a certain step the partial pressure of water vapor in the whole range noted in this work.Practical implications: Based on the developed approach to assessing the propensity to brittle fracture of the formed cermet microstructure, it is possible to obtain an anode material that will provide the necessary functional properties of a SOFC. Originality/value: An approach to estimating the propensity to brittle fracture of a formed cermet structure is proposed based on the microhardness and fracture toughness characteristics obtained by the Vickers indentation method

Determination of conditions for loss of bearing capacity of underground ammonia pipelines based on the monitoring data and flexible search algorithms

Purpose: The study aims to diagnose the corrosion current density in the coating defect on the outer surface of the ammonia pipe depending on the distance to the pumping station, taking into account the interaction of media at the soil-steel interface and using modern graphical data visualization technologies and approaches to model such a system. Design/methodology/approach: The use of an automated system for monitoring defects in underground metallic components of structures, in particular in ammonia pipelines, is proposed. The use of the information processing approach opens additional opportunities in solving the problem of defect detection. Temperature and pressure indicators in the pipeline play an important role because these parameters must be taken into account in the ammonia pipeline for safe transportation. The analysis of diagnostic signs on the outer surface of the underground metallic ammonia pipeline is carried out taking into account temperature changes and corrosion currents. The parameters and relations of the mathematical model for the description of the influence of thermal processes and mechanical loading in the vicinity of pumping stations on the corresponding corrosion currents in the metal of the ammonia pipeline are offered. Findings: The paper evaluates the corrosion current density in the coating defect on the metal surface depending on the distance to the pumping station and the relationship between the corrosion current density and the characteristics of the temperature field at a distance L = 0…20 km from the pumping station. The relative density of corrosion current is also compared with the energy characteristics of the surface layers at a distance L = 0…20 km from the pumping station. An information system using cloud technologies for data processing and visualization has been developed, which simplifies the process of data analysis regarding corrosion currents on the metal surface of an ammonia pipeline. Research limitations/implications: The study was conducted for the section from the pumping station to the pipeline directly on a relatively small data set. Practical implications: The use of client-server architecture has become very popular, thanks to which monitoring can be carried out in any corner of the planet, using Internet data transmission protocols. At the same time, cloud technologies allow you to deploy such software on remote physical computers. The use of the Amazon Web Service cloud environment as a common tool for working with data and the ability to use ready-made extensions is proposed. Also, this cloud technology simplifies the procedure of public and secure access to the collected information for further analysis. Originality/value: Use of cloud environments and databases to monitor ammonia pipeline defects for correct resource assessment

Boosting-based model for solving Sm-Co alloy’s maximum energy product prediction task

Purpose: This paper aims to decide the Sm-Co alloy’s maximum energy product prediction task based on the boosting strategy of the ensemble of machine learning methods. Design/methodology/approach: This paper examines an ensemble-based approach to solving Sm-Co alloy’s maximum energy product prediction task. Because classical machine learning methods sometimes do not supply acceptable precision when solving the regression problem, the authors investigated the boosting ML model, namely Gradient Boosting. Building a boosting model based on several weak submodels, each of which considers the errors of the prior ones, provides substantial growth in the accuracy of the problem-solving. The obtained result is confirmed using an actual data set collected by the authors. Findings: This work demonstrates the high efficiency of applying the ensemble strategy of machine learning to the applied problem of materials science. The experiments determined the highest accuracy of solving the forecast task for the maximum energy product of Sm-Co alloy formed on the boosting model of machine learning in comparison with classical methods of machine learning. Research limitations/implications: The boosting strategy of machine learning, in comparison with single algorithms of machine learning, requires much more computational and time resources to implement the learning process of the model. Practical implications: This work demonstrated the possibility of effectively solving Sm-Co alloy’s maximum energy product prediction task using machine learning. The studied boosting model of machine learning for solving the problem provides high accuracy of prediction, which reveals several advantages of their use in solving issues applied to computational material science. Furthermore, using the Orange modelling environment provides a simple and intuitive interface for using the researched methods. The proposed approach to the forecast significantly reduces the time and resource costs associated with studying expensive rare earth metals (REM)-based ferromagnetic materials. value: The authors have collected and formed a set of data on predicting the maximum energy product of the Sm-Co alloy. We used machine learning tools to solve the task. As a result, the most increased forecasting precision based on the boosting model is demonstrated compared to classical machine learning methods

Effects of yttria content and sintering temperature on the microstructure and tendency to brittle fracture of yttria-stabilized zirconia

Purpose: The purpose of this work is to evaluate the propensity to brittle fracture of YSZ ceramics stabilized by the various amount of yttria, based on a study of changes in the microstructure, phase composition, and fracture micromechanisms. Design/methodology/approach: The series of 3YSZ, 4YSZ, and 5YSZ ceramic specimens were sintered in an argon atmosphere. Three sintering temperatures were used for each series: 1450°C, 1500°C, and 1550°C. Microhardness measurements were performed on a NOVOTEST TC-MKB1 microhardness tester. The configuration of the imprints and cracks formed was studied on an optical microscope Neophot-21. The fracture toughness of the material was estimated using both the Vickers indentation method and a single-edge notch beam (SENB) test performed under three-point bending at 20°C in air. The microstructure and morphology of the fracture surface of the specimens were studied using a scanning electron microscope Carl Zeiss EVO-40XVP. The chemical composition was determined using an INCA ENERGY 350 spectrometer. Findings: Peculiarities of changes in the microstructure, the morphology of specimens fracture surface, and mechanical characteristics of YSZ ceramic materials of different chemical and phase compositions sintered in a temperature range of 1450°C to 1550°C are found. Research limitations/implications: To study the actual behaviour of YSZ ceramic materials under operating conditions, it is necessary to evaluate their Young’s moduli, strength, microhardness, and fracture toughness in an operating environment of the corresponding parameters (temperature, pressure, etc.).Practical implications: Based on the developed approach to estimating the propensity to brittle fracture of the formed YSZ ceramic microstructure, it is possible to obtain YSZ ceramic material that will provide the necessary physical and mechanical properties of a wide variety of precision ceramic products. Originality/value: An approach to estimating the propensity to brittle fracture of YSZ ceramics stabilized by the various amount of yttria is proposed based on two methods of evaluating crack growth resistance of materials, namely, the Vickers indentation method and SENB method