Papers by Keyword: Structure

Abstract: Deterioration of metals and alloys due to corrosion has been observed to be a serious challenge in coastal or marine environments. Exposure of mild steel to marine environments often results into dilapidation of physical structure over time. This study addresses the quick response of mild steel failure using NiZnP modified Al₂O₃ functional composite by electrolytic process. The deposition was done with stable pH of 4.5, heated bath temperature of 95°C, stirring rate of 200 rpm and deposition time of 20 min. The materials chemistry of the developed alloy was examined using open circuit potential and linear polarization technique. The structural mechanism and crystal phase formation was characterized using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and X-ray diffraction analyzer. The corrosion results under 3.65% saline environment reveals improved corrosion rate of NiZnP modified Al₂O₃. The surface site of the crystal formation evolves perfectly with hexagonal structure seen along the grain boundaries.

Abstract: The effects of rare earth element Y addition on the structure, elastic modulus and hardness of Ti₈₀Nb_20-xY_x (x =0, 1, 2) alloys were investigated experimentally. The results showed that the structure of Ti-Nb-Y ternary alloys consist of the Ti-Nb matrix and Y-rich precipitates. Increasing the Y content can significantly improve the hardness and elastic modulus decreases with of Ti-Nb-Y alloys.

Abstract: Austempered Ductile Irons is a promising material with a favorable combination of low price and good mechanical properties. It is produced by isothermal hardening of cast iron with nodular graphite. The heat treatment parameters directly influence the structure of the matrix. The structure consists of an ausferrite matrix - a mixture of epitaxial ferrite + residual austenite and graphite. The resulting mechanical properties depend on the proportion and morphology of the individual phases. Therefore, a thorough structural characterisation is needed to describe the influence of the heat treatment parameters. However, conventional methods such as optical microscopy do not provide sufficient accuracy. Therefore, this work used a very accurate EBSD method to evaluate the structure in the as-received state and after heat treatment.

Abstract: This study was carried out to investigate the effects of hydrolysis ratio on the structure and adsorption properties of porous starch. The starches with different hydrolysis ratios were prepared by enzymolysis (combination of α-amylase and glucoamylase), and its adsorption capacity was evaluated by using methylene blue (MB) and soybean oil as adsorption objects. The results suggest that crystallinity, specific surface area and adsorption capacity of porous starch were gradually improved with the increase of hydrolysis degree. The crystallinity of native starch was increased by enzymolysis from 28.43±0.23% to 34.70±0.69%, and the specific surface area was increased from 0.58±0.002 m²/g to 1.82±0.014 m²/g. Moreover, the adsorption capacity toward (MB) was increased from 2.88 mg/g to 3.87 mg/g at 25°C, which was accurately described by the pseudo-first-order kinetic model, and the oil absorption ratio was also greatly improved from 23.2±0.16% to 76.1±0.11%. Thus, the properties of porous starch can be adjusted by controlling the hydrolysis ratio to meet different needs in the market.

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: We investigate the structural evolution of the single-walled carbon nanotubes (SWNTs) by molecular dynamics (MD) simulation using the Gao-Weber potential. The structural evolution of SWNTs is analyzed through the total energy per atom, the radial distribution function, coordination number, bond angle and the distribution of ring statistics. The results show that the melting temperature of SWNTs occurs at around T_m=5620 K. This value is in good agreement with the result of Zhang and co-workers. The visualization indicates that the initially perfect SWNTs is broken resulting in the ring of various.

Abstract: The effect of the quantitative and qualitative composition of mixed binders on the physical and mechanical properties of cement compositions has been experimentally established. A cement stone with a different amount and dispersion of mineral fillers was considered. The research results showed that the plastic strength of the hardening system depends on its initial composition. The defects embedded in the material during its technological processing into the product determine the local stress-strain state of the structure, the nature of cracking and the fracture surface. The effect of technological damage on the mechanical characteristics and the nature of cracking of cement compositions are shown. The possibility of reducing the material consumption of construction materials by 15-21 wt.% due to the use of fillers that are optimal in appearance and quality composition has been proved.

Abstract: The disadvantage of high-strength multicomponent concretes is the high absolute and specific consumption of the binder per unit of strength. The object of research is multicomponent cement systems. The subject is the composition of multicomponent cement systems in order to significantly increase the concentration of the solid phase per unit volume, as well as strength and durability. The creation of a dense, highly filled solid phase in the form of heterogeneous mineral modifiers of a homogeneous dispersed structure ensures the production of high strength concretes with a low binder content. Theoretical and practical studies have shown that there are only three levels of dispersion of mineral modifiers, functionally related to the spatial and geometric parameters of the clinker component and its own pozzolanic activity, providing strength and other construction and technical properties of multicomponent cement systems at the maximum level. The properties and structure of concrete were studied using two fractions of fine aggregate, granite-gabro crushed stone fr. 5-10 mm, Portland cement class CEM I 42.5N, finely dispersed blast-furnace granular slag, microsilica, highly dispersed fraction of cement, superplasticizer Glenium 430 and high-valence hardening accelerator. Research methods: the shape and size of dispersed particles of the components were determined by a laser analyzer, the mobility of the concrete mixture in accordance with GOST 10181–2014, the strength of concrete in accordance with GOST 10180–2012. The structure of the cement stone was studied using scanning microscopy, thermographic and X-ray phase analysis methods. The strength of concrete with an optimized disperse composition, a superplasticizer and a high-valence hardening accelerator at the age of 28 days after hardening under normal conditions was 128; 137; 163 MPa, with the consumption of multicomponent cement, respectively 650, 700, 750 kg / m³.

Abstract: This study is aimed at strengthening the working surfaces of the jewelry tool - scraper. This tool is used for fine cutting work. The object of research is a method of additional thermofrictional hardening of samples of jewelry tool - scrapers made of carbon steel tool grade U8A. In the course of work the complex of metallographic, mechanical and analytical researches of samples in an initial condition after hardening and low-temperature release which includes is carried out which includes:1) preparation of samples in the form of plates and their preliminary heat treatment;2) surface thermofrictional strengthening (STS);3) conducting metallographic analysis of samples; measuring the microhardness and depth of the layer with a changed cross-sectional structure of the samples after STS;4) analysis of the influence of STS on changes in the structure and properties of steel on the basis of the obtained results, as well as identification of the degree of its strengthening and the role of deformation.The methodology of experimental researches is presented. Photographs of samples and some equipment at different stages of the study are given. Data on the distribution of microhardness, photographs of microstructures in cross section of samples after additional strengthening are presented. The efficiency of strengthening of samples after use of additional processing is shown.

Abstract: The paper presents studies aimed at producing a three-component alloy from the powders of cobalt, chromium and molybdenum (66 wt % Co, 28 wt % Cr, 6 wt % Mo), with a stable phase structure by selective laser melting. At the beginning of the work, the initial powders were graded on sieves with mesh sizes of 20-70 µm. The powder mixtures were obtained by mechanical mixing of various fraction powders and mechanical alloying in a planetary ball mill. The samples were produced using the VARISCAF-100MVS selective laser melting unit. The melting process of powder materials was completed in a chamber filled with inert gas argon after preliminary vacuum degassing. The microhardness analysis of the samples before and after the thermal treatment was completed. The results of phase composition studies, X-ray diffraction analysis, scanning electron microscopy are presented. Examination of the X-ray profiles of the samples proves that the obtained alloy mainly contains the epsilon-phase which improves the hardness and the wear resistance of the product.