Materials Science Forum Vol. 1140

Abstract: The effect of heat treatment on the microstructure and mechanical properties of FeCoNiAl_0.25Mn_0.75 high-entropy alloy was investigated. In the as-cast sample, the dendritic microstructure was observed with the FCC lattice, according to XRD analysis. After annealing at 700 °C within 24 hours, the needle-shaped precipitated phase (BCC phase) in the form of clusters along the grain boundaries and in the FCC matrix phase occurs, the fraction of this phase increases significantly and the distribution becomes more uniform when the temperature is increased to 800 °C, the average size of this phase is only about 1-2 µm. However, as the temperature reaches 1000 °C, the BCC phase disappeared and the grain boundary is remelted and looks like cracks. At an annealing temperature below 800 °C, the HV3 hardness of the alloy increases and reaches its highest value of approximately 194 HV3. The yield and tensile strength can reach 373 and 762 MPa, respectively. However, these values decrease significantly when the annealing temperature reaches 1000 °C because of the plastic flow at near-boundary zones. The best relative elongation is 51.2 % at the as-cast state.

Abstract: The study aims to determine the load contributes to changes in the tensile strength of steel P22 at high temperatures. The steel sample was loaded under 95 and 125 N at a temperature of 700 °C for 72 hours. The results showed that the strength of P22 decreased with increasing load. At the temperature of 700 °C, the yield strength (YS) value decreased from 200 to 182 MPa and the ultimate tensile strength (UTS) reduced from 353 to 321 MPa as the load increased from 95 to 125 N. The precipitation of carbide in the matrix of P22 was observed in the steel sample loaded under 125 N at 700 °C for 72 hours. Furthermore, the cavity formation located on the boundary and near the carbide was confirmed when the temperature was 700 °C and the load increased from 95 to 125 N. The cavity was proof of a stress increase near the grain boundary, causing a decrease in the steel’s strength after a certain period of working time at high temperatures.

Abstract: Ferritic 439 stainless steels, known as iron–chromium alloys with chromium content between 11% and 30%, have been extensively used worldwide due to their good corrosion resistance, good formability, high-temperature oxidation resistance, and lower cost compared to austenitic stainless steels. Conventional production processes for these steels, such as melting, casting, and rolling, are predominantly employed due to the material's difficult formability and machinability, especially when producing complex shapes. However, additive manufacturing (AM) offers new processing opportunities. AM technology, specifically Selective Laser Melting (SLM), fuses metallic powders using a precisely focused and controlled laser beam, enabling the production of highly complex parts with high precision. In this work, we present a comparison of ferritic 439 stainless steel manufactured using SLM technology with conventionally manufactured one, focusing on their microstructure, phase, and mechanical properties. The results reveal that SLM significantly increases material strength and hardness due to notable differences in microstructure fineness and phase composition. The rapid solidification during the SLM process results in a microstructure for the as-printed ferritic 439 stainless steel that significantly differs from that of conventionally manufactured ferritic 439 stainless steel. This distinctive microstructure in the additively manufactured product is likely responsible for various other differences in material behavior.

Abstract: The paper outlines a method for comparative analysis of the load-bearing capacity and crack formation of reinforced concrete and fiber-reinforced concrete cylindrical shells based on experimental studies. To implement this task, the authors have developed a special stand. The results of tests of reinforced concrete and fiber-reinforced concrete cylindrical shells, which had the same geometric parameters, are presented. The fiber-reinforced concrete shell had additional dispersed reinforcement with steel fiber with curved ends, which was added at the stage of mixing the concrete mixture in an amount of 1% by volume of concrete. The shells were hinged at four points and loaded with a vertical distributed load applied along four strips, each 13 cm wide, and only along the body of the shell. The load-bearing capacity of the reinforced concrete shell was 101.6 kN, and the first crack appeared at a load of 64.5 kN, which is 63.48% of the load-bearing capacity. Before the loss of bearing capacity, 10 cracks with the same initial opening width of 0.05 mm had formed in the shell. The load-bearing capacity of the fiber-reinforced concrete shell was 149.9 kN, and the first crack appeared at a load of 74.9 kN, which is 49.97% of the load-bearing capacity. Before the loss of bearing capacity, 12 cracks with the same initial opening width of 0.05 mm had formed in the shell. The load-bearing capacity of the fiber-reinforced concrete shell turned out to be 1.48 times greater than that of the reinforced concrete shell.

Abstract: The results of research on the mechanical properties of concrete with the addition of steel fibers of three different types - anchored, flattened and waved - are presented. To study the influence of steel fiber on the mechanical characteristics of fiber concrete, standardized samples were made and the following tests were carried out: cubes for chipping and compression; compression prism; figure eights for stretching; prism for tension in bending. Different types of steel fiber show unequal increases in strength. The most profitable from this point of view is the addition of anchor fiber to concrete, the least - wave fiber. But the presence of any of the considered steel fibers in the composition of the mixture significantly increases the strength of the sample. The obtained values of tensile strength when splitting the cubes, depending on the type of fiber, differ from the control concrete samples, respectively: for the anchor fiber by 22.82%, for the flattened fiber – 21.84%, for the wave fiber – 9.59%. The presence of fiber reinforcement has a positive effect on the strength during compression tests of cubes: by 13.01% for anchor fiber, 13.84% for flattened fiber, and 11.47% for wave fiber. It was found that the load-bearing capacity of steel-reinforced concrete under compression practically does not depend on the type of fiber, but the very presence of steel fiber in the concrete mixture from which the prisms were made increases the strength of the sample by an average of 11% compared to concrete prisms. In eight-figure tensile tests, the strength of concrete reinforced with wave fiber fiber gave an increase of 4.1% and 4.4% for reinforcement with anchor fiber. Tensile testing of prisms during bending using steel fiber on average increases the load at the beginning of cracking by 40%, and the load-bearing capacity by 64%. In addition, the type of failure of the sample changes from brittle to viscous.

Abstract: This article is devoted to the modeling of the stress-strain diagram of compressed concrete under the action of dynamic loads of various intensities. The main attention is paid to the influence of the strain rate of concrete on the determining parameters of this diagram. The degree of dependence of the dynamic increase factor (DIF) and the level of critical deformability of compressed concrete both on the rate of its deformation and on the level of elastic-plasticity (class) has been established. The analytical relationship between the main static and dynamic characteristics of the deformation diagrams of compressed concrete is established using the hypothesis of invariance and independence from the load mode of the specific potential energy of the ultimate deformation (destruction) of the material.

Abstract: The main principles of objects of living nature protection from the influence of electromagnetic radiation have been studied. An analysis of various types of protective screens, structures and materials used for their manufacture was carried out. It is proposed to use special concretes based on barium-containing cement with barium hexaferrite aggregate as structural materials to protect the environment from the effects of electromagnetic radiation.

Abstract: Pelletising, i.e. transformation of fine dusty materials into lump materials (pellets, briquettes, pellets), is an important technical task solved in many sectors of the national economy - ferrous and non-ferrous metallurgy, chemical industry and in a number of other industries. The process of pelletising ores and ore concentrates is of the greatest importance for the production of iron and steel, i.e. for ferrous metallurgy. The most common method of pelletising is pelletising - granulation of iron ore concentrates in special granulation plants, usually with the use of binders. As a result of pelletising, so-called pellets are produced, which are subjected to hardening firing (roasting pellets) or achieve the required level of properties without high-temperature treatment (non-roasting pellets) through the use of special binders. The current trend is the transition from firing methods of pellet hardening to non-firing (low-temperature) methods.

Abstract: Cassava shell starch and crab shell chitosan can be used as basic for bioplastics with glycerol and additives such as zinc oxide (ZnO) to improve their mechanical properties. This study used the variables of ZnO percentage and crab shell chitosan mass, which has never been done before. This research process was carried out in several stages, the first was bioplastic synthesis using cassava shell starch, glycerol, and crab shell chitosan with variations of 1 g and 1.5 g with zinc oxide (ZnO) of 3% and 5% of the total mass of starch. The limitations of the research are that the thickness of the tensile test samples is only 0.1-1 mm and the method for making bioplastics is the solution casting method. The second stage is characterization using FTIR to analyze the functional groups of cassava peel starch. Next, observe the morphology on the sample surface using an optical microscope, then a tensile test is carried out to calculate the tensile strength value using the ASTM D882 standard. The results of this research show that the highest tensile strength value for the 1.5 g chitosan and 5% ZnO variation was 10,353 MPa, while the lowest was for the 1 g chitosan and 3% ZnO variation at 4,526 MPa. The elongation value obtained was the highest in the variation of 1.5 g of chitosan and 3% zinc oxide at 10.508%. Meanwhile, the lowest ductility value was found in specimens with variations of 1 g of chitosan and 5% zinc oxide, amounting to 6.716%. The level of water resistance from the swelling test was found to be the highest with the 1.5 g chitosan and 5% zinc oxide variation with water absorption of 23.14%, however, the highest water absorption of 39.36% was obtained with the 1 gr chitosan and zinc oxide variation 3%. Optical microscope testing on the surface of samples of variations of 1.5 g chitosan and 5% zinc oxide showed the best physical properties. Therefore, the addition of reinforcement in the form of chitosan and zinc oxide affects the tensile strength value of the bioplastic film, where the higher the amount of reinforcement used, the higher the strength value produced.