Key Engineering Materials Vol. 973

Abstract: Biological pollution creates significant obstacles in the operation of power plants' technical water supply cooling systems (SCS). To minimize biological pollution, methods of corrective treatment with biocides are implemented. While these biocides effectively prevent fouling of the cooling system, they can also adversely affect the environment and structural materials. By evaluating structural materials' corrosion resistance and biocides' environmental safety for the cooling water during biocide treatment, any potential issues can be identified and addressed before they become a safety or operational concern. The paper presents the results of bench tests of the corrosion resistance of structural materials SCS, corrosion aggressiveness of the biocides: sodium hypochlorite NaClO and 2, 2-dibromo-3-nitriloropionamide (DBNPA), and the results of measurements of the concentration of biocides and their decomposition products to assess compliance with environmental standards when discharging return water when applying from biocides treatment. The cooling water SCS of the Rivne NPP (Nuclear Power Plant) was chosen as the research object. Bench corrosion tests were carried out using samples of corrosion indicators from materials: steels Ст20, 08Х18Н10Т; copper alloy МНЖ-5-1 and aluminum, which are defined as analogs of structural materials of the technical water supply system of the Rivne NPP. The conditions of operation of the technical water SCS of the Rivne NPP were simulated on the test bench, and corrosion rate measurement was carried out by the gravimetric method.

Abstract: A straightforward technology for the thermal cyclic processing of the Fe-C melt has been developed to induce significant super-cooling before crystallization. Eutectic crystallization of pro-eutectic alloys under substantial super-cooling is demonstrated to be a complex process, comprising several partial crystallization processes and the synchronous dissolution of crystalline phases: austenite and two metastable carbides, Fe₃C and Fe₇C₃. The kinetics of the eutectic transformation L→L+Fe₇C₃ in its microscopic and thermal (DSC) imaging has been studied. In general, crystallization proceeds according to the scheme L→L+Fe₇C₃+γ→L+Fe₇C₃+γ+Fe₃C→ Fe₇C₃+γ+Fe₃C. Consequently, plate-like eutectic (Fe₇C₃+γ) with an austenite matrix and ledeburite (Fe₃C+γ) with a cementite matrix are formed. A schematic diagram of the metastable phase equilibria in the Fe-C system is provided. In the conducted experiments, phase transformations occur in two subsystems: Fe-Fe₃C (at low supercooling) and Fe-Fe₇C₃ (a subsystem of metastable equilibria of the second, higher degree of metastability at large supercooling). This is confirmed by the replacement of the carbide phase and different equilibrate concentrations of austenite in metastable equilibrium with each of the carbides.

Abstract: The study presents mechanical performance metrics, especially, energy absorption, of aluminium foams fabricated by melt processing with CaCO₃ blowing agent without Ca additive. Relatively ductile Al1Mg0.6Si alloy and high strength Al6Zn2.3Mg alloy comprising brittle eutectic domains were employed for the foams manufacture and then examined in conditions of uniaxial quasi-static compression. It was recognized that mechanical response of the foams and energy absorption is radically defined by the mechanism of cell collapse which, in turn, depends on the nature of structural constituents of the cell wall material. In particular, the presence of brittle eutectic domains in the cell wall material of foam based on Al6Zn2.3Mg alloy results in reducing the compressive strength and energy absorption compared to those of foam processed with Al1Mg0.6Si alloy, both deviate markedly from the theoretical predictions. In spite of this experimental verification of foams cell collapse is considered to be strongly required before their engineering application.

Abstract: Sintered Ti6Al4V titanium alloys prepared from TiH₂/60Al40V powder blends under various technological conditions were studied. The microstructural evolution was investigated by X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray analysis. The corrosion resistance of sintered titanium alloy was evaluated by the static immersion test in 40 wt.% H₂SO₄ acid, according to ASTM standard G31-72(2004). Depending on powder metallurgy processing parameters (compaction pressure or sintering temperature), the Ti6Al4V alloy was obtained with various structural features (porosity and structural heterogeneity). It was shown that those structural features of sintered Ti6Al4V titanium alloy are a key microstructural factor that determines their corrosion resistance. For instance, an increase in porosity leads to enhanced corrosion resistance. Based on the current research, the optimal manufacturing regimes of powder metallurgy of Ti6Al4V titanium alloy ensure the achievement of characteristics sufficient for practical use in aggressive conditions of the chemical industry were obtained.

Abstract: This study investigates the impact of lubrication on friction factors during the hot ring compression test of BS 080M46 medium carbon steel. Hot forging processes are crucial in industries due to the strength and durability of forged products, but friction-related issues can arise. Four lubrication conditions are focused: dry, oil to black graphite, water to black graphite, and water to colorless graphite. The ring compression test procedure, including sample dimensions and lubrication application, is explained. By employing predictive calibration curves generated through FEM which monitored height and internal diameter changes during compression. The study successfully aligns FEM simulation results with experimental data, thereby enhancing the accuracy of friction factor estimations and visualizing material behavior under various lubrication conditions. Results indicate that lubrication significantly affects friction factors, with oil to black graphite performing the best, yielding a friction factor of 0.15. A comparison between theoretical and experimental friction factors shows varying agreement levels, with water-to-black graphite, and water-to-colorless graphite respectively demonstrating excellent alignment with 0.990% and 0.971%. This study has practical implications for selecting lubricants in industrial applications, potentially enhancing manufacturing processes and product quality.

Abstract: The microstructure of AZ91 (Mg-Al) alloy is comprised of α-Mg and β-Mg₁₇Al₁₂ massive phase. The lower melting point associated with the β-Mg₁₇Al₁₂ phase results in poor creep resistance of the alloy. In the present study, the AZ91 alloy with the addition of calcium (Ca, 1wt%) and cerium (Ce, 1wt%) is cast, and their effect on the microstructure and creep behavior of AZ91 alloy have been investigated. Thermally stable phases such as Al₂Ca and Al₁₁Ce₃ are introduced in the AZ91 alloy through the addition of Ca and Ce elements. Energy dispersive spectroscopy (EDS) and x-ray diffraction analysis confirmed the presence of these intermetallic phases in the microstructure. Tensile creep tests on the as-cast samples were performed at 175^°C temperature under 50 MPa stress. The study shows that the creep resistance of AZ91 alloy is greatly improved with the presence of Al₂Ca and Al₁₁Ce₃ intermetallic phases because of their better thermal stability than β-Mg₁₇Al_12.

Abstract: The main theoretical aspects of porous and powder materials technological processing is worked out. The proposed material model is based on: - the four-parameter plasticity theory, which reflect the influence of porosity, resistance and the presence of dilatancy of solid phase deformation regime; - the dissipative potential and the load surface expression, that allow to take account such materials elastic - viscous - plastic properties; - the solid phase energy deformation speed with its subsequent over the representative element volume averaging. The peculiarity of this model is that the equilibrium flow concept elastic-viscous-plastic material is an alternative to its elastic-plastic deformation. The proposed equations are suitable for their effective practical using for digital models creation that based on existent software for the of equilibrium processes of compact materials deformation finite–element analysis. The practical use of the proposed methodologies made it possible to determine: - the regularities of the different modules material layers interaction during stamping of bimetallic blanks with an conical working surface; - the porosity distribution over the product volume at the final stage of radial extrusion of the bushings with an internal flange; - the effect of powder material decompression during reverse extrusion of cylindrical products.

Abstract: The main objective of this work is to optimize welding parameters of AISI 430 FSS welds, focused to minimization of ferrite grains size using Taguchi’s design. Two input parameters of speed and welding current; were chosen to select the minimum grain size and to ascertain their effects on ferrite grain size. ANOVA method was used to evaluate the influence of varying factors on the overall quality of welds. Optimal combination of the parameters were be predicted by S/N analyses, it was accessed on employing an 80 A with 6mm/s. Experimental characterizations of optimum weld joint were performed by using tensile test assisted by image correlations, optical and electronic microscopy. As a result, welding speed had the main influence on grain size by 84.30%. Optimum welding parameter offered finest microstructure with low rate of martensite precipitates in both fusion zone and heat affected zone, and best combination of strength and ductility, it presented a homogeneous distribution of tensile stresses that caused a ductile fracture in base material. ,it is found that that optimized welding parameters permit to give greater resistance to corrosion, which exhibit a lower corrosion current, indicating that coarse ferrite grains are more susceptible to corrosion compared to fine grains.

Abstract: Controlling the movement of liquid metal by selecting the parameters of an external electromagnetic effect makes it possible to change the conditions of dynamic equilibrium of the weld pool and, as a result, the formation of a weld. Magnetic process control has advantages over mechanical control methods, since it is carried out without contact with the welding zone. The study of processes leading to a decrease in the concentration of defects in metals, recombination of dislocations, polygonization, recrystallization, defect healing, etc., is an urgent task for technologists. The purpose of the work is to study the laws of formation of phase composition, microhardness, grain, lath, subgrain, dislocation structures of low-alloy steel welds in underwater welding and the relationship of structural parameters with the properties of strength and crack resistance of these joints. Microstructure studies were carried out by light, scanning, and transmission electron microscopy. Mathematical modelling was carried out to optimize the research efficiency. The developed computer application implements the idea of sequential calculation of quantities, where the value of the welding current and the current in the inductor is selected by the researcher. The influence of structural factors at the dislocation level on local internal stresses, which determine the deformation localization zones in the structures of the upper and lower bainites in the deposited metal, is analyzed. The conditions for obtaining high-quality welded joints in the welding of low-alloy steels, which ensure their strength and crack resistance, are established.