Increase In Strength Characteristics Research Articles

EFFECT OF SEVERE PLASTIC DEFORMATION AT HIGH TEMPERATURE ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FERRITIC-MARTENSITIC STEEL T91

The microstructure and mechanical properties of ferritic-martensitic steel T91 after severe plastic deformation (SPD) and subsequent annealing (tempering) have been studied. The SPD of steel T91 was carried out by the method of multiple “upsetting-extrusion” at a temperature of 875 °C, subsequent annealing was carried out in the temperature range of 550...650 °C for 1…100 h. It has been found that the multiple “upsetting-extrusion” process allows the formation of an ultra-fine grained structure with an average grain size of 110 nm, which remains stable at the annealing temperatures of 550 and 600 °C for up to 100 h of exposure. After annealing at these temperatures, the microhardness remains at the level 3100 and 2780 MPa, respectively, which is noticeably higher than with standard N&T treatment of this steel (2480 MPa). The refining of grain and MX-type carbide precipitates, due to severe plastic deformation, also leads to an increase in strength characteristics during tensile tests at temperatures of 20 and 600 °C which are significantly higher than after standard N&T treatment.

Gradient microstructure formation in carbon steel bars

In recent years, severe plastic deformation has been one of the most popular methods of increasing the mechanical properties of bars. Obtaining an ultra or nanostructure in such bars provides high strength properties, but also reduces plasticity. This paper shows that gradient structure formation in carbon steel bars gives a simultaneous increase in strength properties and some decrease in plastic properties. A new combined technology is proposed for obtaining gradient microstructure. This technology consists of drawing medium carbon steel bars on a radial-shear broaching mill and subsequent drawing. Bars with 30 mm diameter were strained at room temperature to a diameter of 16 mm in 3 passes. As a result, during three straining cycles, the average value of microhardness in the central zone was 2085 MPa, in the neutral zone was 2505 MPa, and in the surface zone was 2915 MPa. This variation of microhardness confirms gradient microstructure availability. Also there was an increase in strength characteristics almost 2 times, plastic characteristics undergo reduction due to gradient microstructure obtained during straining, but remain at a fairly good level for steel AISI 1045. The validity of the results is confirmed by a large number of experiments using a set of standard and modern research methods, such as optical, scanning and transmission microscopy, EBSD analysis, microhardness changes, fractographic method and tensile tests of mechanical properties, as well as by the results reproduction in the joint use of methods.

FUNCTIONAL AND MECHANICAL CHARACTERISTICS OF ULTRAFINE-GRAINED FE-MN-SI ALLOYS FOR BIOMEDICAL APPLICATIONS

This work examines the possibility of regulating the corrosion rate of Fe-Mn-Si alloys by modifying their structure via equal channel angular pressing. It is found that the formed ultrafine-grained austenitic structure of Fe-Mn-Si alloys leads to a significant increase in strength characteristics at satisfactory ductility. The presence of special twin boundaries in the structure of Fe-Mn-Si alloys improves their corrosion resistance, while a predominantly grain-subgrain structure in the absence of twin boundaries increases the corrosion rate up to 0.4 mm/year. The shape memory effect in the studied alloys manifests itself at temperatures unacceptable for medical use. Structure refinement by equal channel angular pressing in modes that ensure a completely austenitic state leads to a decrease in shape memory properties.

Механические характеристики реставрационных растворов при использовании в их составах метакаолинов

Purpose: To analyze the possibility of using highly active metacaolines in the compositions of gypsum-lime binders for restoration work. To consider the compatibility of the components of restoration solutions based on the reproducibility of their main characteristics, such as mineralogical and chemical composition, physical and mechanical properties and durability. Methods: The work uses physico-chemical research methods, as well as methods of comparative analysis, in accordance with the guidelines of GOST 125-2018 “Gypsum binders. Technical conditions”. Results: It is shown that the introduction of metacaolin into the binder compositions provides an increase in the strength of the binder stone. The optimal amount of metacaolin is 20% in a gypsumlime mixture. It has been experimentally established that an increase in the content of Al2O3 in metacaolin from 39 to 44% leads to an increase in the early compressive strength of a stone made of modified gypsumlime binder. An increase in the content of Al2O3 leads to an increase in strength characteristics. Practical significance: The conducted studies demonstrate that such indicators as the average particle size, specific surface area, have an impact on the hydraulic activity of the pozzolan additive. The quality of highly active metakaolins is directly dependent on the degree of purity of kaolin. However, additives may differ in the mass content of oxides, in particular the content of the main oxides SiO2 and Al2O3. The use of highly active metacaolines in the compositions of gypsum-lime binders makes it possible to restore architectural monuments.

Study of Gas Swelling Processes under Irradiation with Protons and He2+ Ions in Li4SiO4–Li2TiO3 Ceramics

One of the important areas of research in the energy sector is the study of the prospects for using new types of nuclear fuel, including tritium, which is one of the most promising types of fuel for thermonuclear energy. At the same time, for the production of tritium in the required quantities, the one that is the most optimal is the use of blanket materials based on lithium-containing ceramics. This is where tritium is released from lithium under the influence of neutron irradiation. The paper presents the results of an investigation of the influence of two-phase ceramics based on Li4SiO4–Li2TiO3 compounds on the resistance to external influences (mechanical loads) during the accumulation of hydrogen and helium (He2+) in the near-surface layer. The interest in such studies is primarily related to the search for solutions in the field of creating high-strength materials for tritium generation for its further use as nuclear fuel for thermonuclear fusion, as well as to the study of the mechanisms of the influence of different phases on the changes in the strength properties of ceramics, which provides an opportunity to expand fundamental knowledge in this area. The proposed method of obtaining two-phase ceramics by mechanical-chemical mixing and subsequent sintering into spherical particles enables the production of well-structured, high-strength ceramics of specified geometric dimensions (limited only by the dimensions of the mold) with a controlled phase ratio. During the experiments, it was found that increasing the content of Li4SiO4 phase in ceramics leads to an increase in strength characteristics (hardness, resistance to cracking) by 15–20% compared to single-phase ceramics. The most optimal composition of two-phase ceramics with high resistance to destructive embrittlement is the ratio of phases 0.75Li4SiO4–0.25Li2TiO3. One of the factors explaining the increase in resistance to destructive embrittlement under high-dose irradiation for two-phase ceramics is the increased dislocation density and the presence of interphase or intergranular boundaries, the high concentration of which leads to the creation of additional obstacles to the agglomeration of hydrogen and helium in the near-surface layer.

Оптимизация схемы армирования трубы при деформации растяжения с учетом критериев оптимальности

The article discusses the optimization of a pipe reinforcement scheme under tensile deformation. In the Siemens NX environment, a model is created and an analysis of the stress-strain state is carried out, trajectories of reinforcement laying are identified, and a reinforcement scheme is created. The resulting scheme is brought to the optimal by applying the optimality criteria. The main criteria for fixed structures include the given mass criterion and the maximum displacement and stress criteria. Various options for transforming the reinforcement scheme are considered. By maintaining a balance between an increase in strength characteristics and a decrease in the mass of the structure, an optimal reinforcement scheme has been achieved. Ultimately, a reinforcement scheme has been developed that satisfies the specified optimization criteria.

Selective Laser Melting of Inconel 718/TiC Composite: Effect of TiC Particle Size

In this article, we present the results of a study of the effect of TiC particle size on the microstructure and properties of a composite material based on the heat-resistant nickel alloy Inconel 718. Composite materials with the addition of 1% mass of micron- or nano-sized TiC particles were successfully manufactured by selective laser melting. Hot isostatic pressing and heat treatment were applied to manufactured samples. Increasing hardness with the addition of TiC particles by about 20% without dependence on TiC size was determined. The addition of nano-sized TiC leads to a greater increase in strength characteristics at room temperature and elevated temperature of 700 °C in comparison with pure Inconel 718 and the addition of micron-sized TiC particles, but also leads to decreasing elongation.

Influence of the Chemical Activation of Aggregates on the Properties of Lightweight Vibro-Centrifuged Fiber-Reinforced Concrete

One of the most essential building materials for sustainable development is concrete. However, there is a problem with a lack of inexpensive, efficient ways to make it high-strength and ultra-dense. A promising direction is the additional processing or activation of the cheapest component of the concrete mixture—inert aggregate. The article is devoted to a promising method for the simultaneous activation of both large and small aggregates using vibro-centrifuge technology. It has been established that the activation of concrete aggregates with aqueous solutions of natural bischofite at a concentration of 6 g of dry matter per 1 L of water is the most rational and contributes the maximum increase in strength characteristics and the best values of strain characteristics. Strength characteristics increased up to 16% and ultimate strains increased to 31%, respectively, and the modulus of elasticity increased to 9%. A new improved lightweight fiber-reinforced concrete was created and an innovative technology is proposed that makes it possible to achieve savings in manufacturing due to a significant improvement in structural properties and reducing the working sections of reinforced concrete elements. Regularities between the fundamental chemical processes of the surface activation of aggregates and the physical processes of structure formation of compacted and hardened concrete were revealed. An improvement in the structure of concrete at the micro- and macro-levels was recorded due to a point decrease in crack formation at the interfaces of the “cement matrix-aggregate” and “cement matrix-fiber” phases, and a decrease in the number of micropore defects was also found. Economic efficiency reached 25–27%.

Cement and claydite dust binding compositions

Introduction. The article presents the production results for binder compositions of the optimal proportion based on Portland cement and claydite waste – claydite dust. The granulometric composition studies have been conducted, test results for binder compositions of different proportions are presented: cement – claydite dust, jointly mechanically activated in a vibrating mill. The binder compositions with a wide range of use have been developed and determined. Using the electron microscopy method, microphotographs of cement stones chips made from Portland cement and different contents of claydite dust, which have been mechanically activated in a vibrating mill, were taken. There is active overgrowth of open pores in cement stones obtained from binder compositions by neoplasms of various sizes.After the use of claydite dust as a raw mix, the structure of the composite is compacted.Materials and methods. ЦЕМ0 52.5N Portland cement (GOST 31108-2020) produced by ZAO Belgorodskii Cement and claydite dust, the waste of claydite dust production, were used in the work. The mechanical activation was performed by grinding in a vibrating mill. The normal density was determined using the Vic’s device according to GOST. The granulometric composition was studied using the AnalyssetteNanoTecplus device. The microstructure was studied using a high-resolution scanning electronic TESCAN MIRA 3 LMU microscope. In order to construct diffractograms, the ARL X’TRA Thermo Fisher Scientific device was used.Results. The binding composition of the optimal proportion of claydite dust demonstrates an increase in strength characteristics, there is a compaction of the cement stone structure compared to ordinary Portland cement.Discussion and conclusions. The use of waste from the production of claydite – claydite dust as a mineral filler of the binder composition makes it possible to save expensive Portland cement, while increasing the strength characteristics of the binder composition.

Enhanced Eco-Friendly Concrete Nano-Change with Eggshell Powder

One of the unifying factors for all countries is the large consumption of chicken, and other, eggs in food and other types of economic activity. After using various types of eggs for their intended purpose, a large amount of waste accumulates in the form of eggshells. Currently, this problem exists and needs a non-trivial, original solution. The aim of the work was to fill the scientific gap in the direction of studying the microstructure formation of improved nano-modified environmentally-friendly concrete based on eggshell powder and obtaining a concrete composition for the manufacture of an industrial sample of such a material. An environmentally-friendly concrete was obtained, the characteristics of which were improved relative to standard concrete by modifying it with eggshell powder, for which the optimal dosage was determined. The most effective was the replacement of part of the cement with eggshell powder in the amount of 10%. The maximum increase in strength characteristics ranged from 8% to 11%. The modulus of elasticity increased by 4% compared to the control samples without eggshell powder. The maximum reduction in deformations under axial compression and tension in comparison with the control values ranged from 5% to 10%. The study of the composite’s microstructure nano-modified with eggshell powder, and an analysis of the changes occurring in this microstructure due to nano-modification, confirmed the improvement in characteristics and the optimal dosage of eggshell powder.

Non-destructive testing of physical and mechanical properties of local zones in welded joints

The influence of the “saw-tooth” type electron beam sweep on the penetration shape during electron-beam welding of 30KhGSA high-strength steel with different welding modes was investigated. Using the instrumented indentation method, the distribution of Young’s modulus, as well as the characteristics of strength and plasticity in the welded joints cross-sections, was obtained. It has been found that in the weld metal there is a sharp increase in strength characteristics, while the plasticity ones are significantly reduced. The values of the Young’s modulus also varied over the cross-sections. The considerable decrease in this characteristic (up to 20%) was registered in the weld metal in comparison with the parent metal results.

High-Performance Concrete Nanomodified with Recycled Rice Straw Biochar

The development of new and improvement of existing technologies based on the use of waste products from various industries or recyclable materials is a current trend in the construction industry. Including in the composition of binders and concrete by-products of industry, reducing the proportion of Portland cement, it is crucial to maintain and improve the resulting products’ mechanical characteristics and life cycle. The main aim of the study was to investigate the influence of biochar additive on the microstructure and properties of the concrete and obtain the composition with improved characteristics due to nanomodification of rice straw recycled biochar. An environmentally friendly technology for concrete manufacture was obtained, using agricultural waste, rice straw, as its components, developing a composition of concrete nanomodified with processed rice straw biochar, identifying the dependences of concrete properties on their nanomodification with processed rice straw coal. It has been established that the most effective dosage is the addition of rice straw biochar in the amount of 6% by weight of cement. The improvement in the properties of concrete was expressed in the increase in its physical and mechanical characteristics and changes in deformability according to the results of the analysis of the stress-strain diagrams. The increase in strength characteristics ranged from 17% to 25%. The modulus of elasticity increased to 14%. The deformation characteristics decreased from 12% to 24%. Introducing a finely dispersed additive of rice straw biochar modified by the electromagnetic method leads to a decrease in cement consumption by up to 10%.

Improving safety during operation of gas turbine units

This article considers the possibility of improving the safety during operation of gas turbine plants due to improving the strength characteristics of rotor blades, by using ultra-finegrained ferrite-martensitic steel of the EI-961 class for their manufacture. It is known that one of the main elements of stationary gas turbine plants is rotor blades made of EI-961 steel, which is a typical representative of ferrite-martensitic steels. Due to the fact that the blade complex determines the safety and service life of gas turbine plants, improving the strength characteristics of ferrite-martensitic stainless steels, it is important and relevant to increase the reliable and safe operation of such plants. As a result, studies have been carried out using EI-961 - stainless heat-resistant high-alloy martensitic-grade chromium-nickel steel as the starting material. To form an ultrafine structure, the samples were subjected to intense plastic deformation followed by heat treatment. It was revealed that the use of intense plastic deformation by torsion and equivocal angular pressing led to a significant increase in the microhardness of steel EI-961, which in turn leads to an increase in strength characteristics. To evaluate the mechanical properties, tensile tests of standard samples were carried out, which showed that additional re-hardening of samples after standard thermal treatment of martensitic steel EI-961 led to an increase in strength, it is clear that in an ultrafine state, the strength gain is greater than in coarse-grained (in an ultrafine state - 30%, coarse-grained - 11%), while maintaining ductility 5%.

PRODUCTION OF POROUS GLASS-CRYSTALLINE MATERIALS BASED ON GLASS CULLET AND CONVERTER SLAG

The study conducted the research aimed to obtaining a porous glass-crystalline materials based on glass cullet and converter slag, which was used as a gas-forming additive. In this work, the chemical and phase compositions of the studied slag were analyzed, and a differential thermal analysis of its sample was carried out. Converter slag was added to the composition of the masses in an amount of 2.5 to 30 wt%, the rest was glass cullet. Вurning of the samples was carried out in the temperature range of 850-925 ° C. For the samples under study, using a sand volumetric meter, the volume was determined and the swelling coefficient was calculated, the compressive strength was determined, and the type of structure, which depends on the average diameter of the prevailing pores, was analyzed. The dependence of the swelling coefficient of the investigated materials on the burdening composition and burning temperature has been established. To obtain porous materials with a swelling coefficient of 2.16-2.67 and uniform fine-porous structure (predominant pore size less than 0.5 mm), it is optimal to introduce converter slag into the composition of the masses in an amount of 10-15 wt%, and the recommended temperature range their burning 850-900 ° C. Analysis of the phase composition of the materials obtained indicates the presence of wollastonite as the main crystalline phase, which, due to the acicular structure of the crystals, has a reinforcing effect and contributes to an increase in strength characteristics. The developed porous glass-crystalline materials can be used as thermal insulation and aggregates in lightweight concrete.

Influence of thermoactivation on properties of mineral additives in dry mixtures

Information on the effect of thermal activation of silicate and aluminosilicate rocks used as a filler in dry building mixtures on their reactivity of interaction with lime binder is presented. The change in the distribution of acidic Bronsted and Lewis centers on the filler surface as a result of thermal activation is shown. It was found that the number of Bronsted and Lewis acid centers on the surface of fired clays exceeds the number of the same centers on the surface of unbaked clays. The number of adsorption centers at pKa from 0 to 7 and pKa> 13 on the surface of fired diatomite is 2.435 * 10-5 mol/g, and on the surface of unbaked diatomite -1.678 * 10−5 mol/g. The heat treatment of diatomite at low temperatures (2000C and 3000C) does not significantly affect the values of the compressive strength of the mortar. An increase in the firing temperature to 7000C leads to an increase in strength characteristics up to R = 4.38 MPa. However, the greatest effect is achieved when diatomite is fired at a temperature of t = 9000C. The value of the ultimate strength in compression was R = 5.1 MPa.

Impact of nanomaterial on lake soil strength parameters and its application as subgrade an experimental analysis

The main motive of this research paper is to study the stabilization of sediment soil by utilizing a cementitious nanomaterial called Alccofine. Sediment soil is known to weaker in nature and has low shear strength due to presence of clayey sediments in large amount by volume. Clay soil is known to be problematic in nature. It is highly cohesive, has low shear strength and undergoes change in its volume with the change in its moisture content i.e., swelling and shrinkage with increase or decrease in water content, respectively. This type of soil, when used as a subgrade in construction of flexible pavements, can result in excessive cracking, loss of strength and hence can cause severe damage to the flexible pavement over time. In light of such behaviour of the sediment soil, an attempt has been made to enhance the engineering characteristics of the soil using Alccofine [1108]. Being a nano particle, Alccofine thoroughly blends with the sediment soil ensuring homogeneity throughout. Alccofine is added to the soil in various proportions i.e., 3%, 6%, 9%, 12% and 15% by weight to stabilize the soil. Unconfined Compression Strength test and California Bearing Ratio test were, then, conducted on the soil which revealed the increase in strength characteristics of the sediment soil.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF OXIDE DISPERSION STRENGTHENED HIGH-ENTROPY ALLOYS CoCrFeMnNi AND CrFe2MnNi

High-entropy alloys (HEAs) CoCrFeMnNi and CrFe2MnNi, dispersion-strengthened by pre-synthesized nanooxides composition of 80%Y2O3+20%ZrO2 (mol.%) were obtained by mechanical alloying followed by compaction and sintering. Average grain size of the oxide dispersion-strengthened (ODS) alloys was about 2 μm. Oxide precipitates in alloys are characterized by the presence of small particles with an average size of about 10 nm and a density of ≈ 1021 m-3, as well as small amount of larger particles sizes of 50…150 nm. The qualitative composition of particles of different sizes has been established. Mechanical properties of HEAs were studied at different temperatures. It is shown that strengthening of the studied alloys by nanooxide particles leads to a significant increase in strength characteristics.

Analytical optimization of the dispersion-reinforced fine-grained concrete composition

The article presents the results of studying the problem of the concrete scrap accumulation and disposal. It is noted that after the implementation of comprehensive programs, including the renovation and modernization of the housing stock, a significant amount of concrete scrap has already been accumulated, and its amount will only increase. The results of scientific research on the compositions development of composite binder and fine-grained dispersed reinforced concrete based on this binder are presented. The purpose of the research described in the article was to develop the elements of a methodology for selecting the dispersed reinforced composite material composition based on finely ground waste of concrete scrap, mineral binder, thin basalt fiber and superplasticizers. The goal was solved using the methodology of technological processes system analysis and, in particular, mathematical planning, processing the experimental results and applying the analytical optimization method. It is noted that fine grinding of mineral components and the use of fibers with a diameter of 0.1 … 6 microns allows not only to modify the concrete structure with an increase in strength characteristics, but also changes the chemical and physicochemical processes‘ nature on the contact surfaces of the mineral matrix and fiber, as well as the same binder and finely ground reactive mineral particles with the formation of microsystems qualified as nanostructures.

ЦИФРОВОЕ РЕГУЛИРОВАНИЕ ПАРАМЕТРОВ В СИСТЕМЕ АВТОМАТИЗИРОВАННОГО УПРАВЛЕНИЯ ПРОИЗВОДСТВОМ АСФАЛЬТОБЕТОННОЙ СМЕСИ

Relevance The development of the region is reflected in its socio-economic policy and depends on the projected gross domestic product growth data, which affects the increase in freight traffic by road. In the Republic of Bashkortostan, by 2030, the volume of such traffic may grow by 30–40 %, while the number of freight transport will double. The number of personal vehicles of the population of the region will reach the level of 300–350 vehicles per 1000 inhabitants. All these data will certainly lead to an increase in the intensity and density of traffic on transport arteries, both regional and inter-municipal significance by 30–40 %. Already today, about 80 % of the length of transport arteries of regional municipal significance need to increase the strength indicators due to the accelerated wear of the roadway and a decrease in the service life between scheduled repairs. In the course of the implementation of the national project of the Russian Federation «Safe High-Quality Roads», the capacity of highways in the republic is insufficient, and the quality of highways requires an increase in strength characteristics. Therefore, the development of new approaches to the functioning of information systems is becoming in demand and makes it possible to simulate the interaction of subsystems of an automated control system (ACS): ACS for supplying mineral materials and ACS with sand and crushed stone bins will allow us to assess the complexity of organizing the interaction of ACS subsystems. The foregoing sets the task of improving the quality of the asphalt concrete mixture at the output of the asphalt concrete plant, which is ensured by the automation of the enterprise. Therefore, the task of developing a distributed hierarchical control system for information systems of the asphalt concrete plant is urgent. Aim of the research Creation of a methodological basis for the development of structures for modern management systems for the production of asphalt concrete mix. Research methods The research is based on a set of methods of the theory of probability and mathematical statistics, optimal systems and mathematical modeling, as well as the theory of automatic control. Modeling of the technological process and system analysis was carried out using the MatLab package. Results The solution of problems of digital control of asphalt concrete production in the form of a generalized approach is presented. All data on raw materials and technological process are collected in a single database, which allows them to be processed at a new level. The result of the research carried out makes it possible to apply the proposed concept and methodology to further research, which will lead to the development of the optimal structure of the ACS in the construction industry. The introduction of new research results will improve the assessment of the effectiveness of solutions for the technical re-equipment of asphalt concrete plants ACS.

The use of nanosized additives in the modification of brick loam

The effect of nanosized additives on the strength properties of ceramics based on fusible brick loam of the Klyuchischenskoye deposit has been studied. In general, all nanosized additives selected for the study had a positive effect on the strength properties of ceramics. The greatest increase in strength, when using nanosized silica ash Laksil 30, was 70 %, in relation to the control sample. When using silica ash, an increase in the content of the amorphous phase in the shard after firing is noted against the background of a decrease in its porosity, which causes an increase in strength characteristics. The nature of the destruction of the samples also differed. The destruction of the control sample was accompanied by the formation and gradual opening of cracks. The destruction of the modified samples was more fragile in comparison with the control. Thus, the effectiveness of nanosized additives on the strength properties of ceramics is shown.