Papers by Keyword: Microstructure

Abstract: The structural-phase compositions of the alloy obtained through reduction melting with oxide waste use from the production of high-alloy steels and alloys with different charge compositions have been studied. It is crucial to determine the technological parameters that ensure the reduction of alloying element losses during the production and use of the alloying material. In the phase composition of the resulting alloy, a solid solution of alloying elements and carbon in the lattice of γ -Fe, Fe3C, as well as FeNi in the case of adding alloyed metal chips to the charge has been found.At the same time, a relative increase in the content of alloying elements in the studied areas of the alloy has been ensured (wt.%): Cr – from 1.84–32.90 to 0.59–43.98; Ni – from 1.41–20.74 to 4.24–45.02; Mo – from 0.35–1.30 to 0.00–11.89; W – from 0.00–0.08 to 0.00–21.37, respectively. This led to the formation of new phase structures containing refractory elements, presumably of carbide and intermetallic nature, which been observed in microstructural images. The proportion of residual carbon in the form of carbide component and residual unreacted reductant is aimed at providing the required reducing capacity during the alloy usage. The studies have identified new technological aspects of processing high-alloy industrial waste, resulting in a resource-efficient alloying material with the potential to partially replace standard ferroalloys in steel production.

Abstract: The primary objectives include investigating the mechanical properties of used construction steel, and evaluating the feasibility of reusing the old materials in green construction projects. The methodology involves gathering samples from demolition sites which are over 40 to 50 years old(1980-1985 construction sites), conducting mechanical testing (such as tensile test and bending test), and performing microstructural analysis.By promoting the utilization of used construction steel, the project seeks to reduce waste, lower material costs, and minimize the environmental impact for sustainable activities. The results we found were that the average maximum load the material can bear was 1.35KN and was bended till 6mm. The average grain size of the material was found to be 20µm. the average elongation percentage came out to be 15.27% and the elements of the material identifies that it is of grade A-36 Steel.Ultimately, this project aspires to facilitate a shift towards more eco-friendly construction practices and supporting the construction industry's transition to sustainable development.

Abstract: Aluminium alloys are widely used in the automotive and aerospace industries, where permanent fastening methods are commonly employed to join aluminium sheets and components. Many aluminium alloys are known for their high strength-to-weight ratio, while others are favoured for their availability and cost-effectiveness. In modern applications, dissimilar aluminium alloys are often joined to achieve enhanced performance. This study explored the effects of artificial aging on the microstructural and mechanical properties of weld joints at varying temperatures. Significant microstructural differences were observed between the heat-affected zone (HAZ) and the weld zone (WZ). Coarse grains in the HAZ enhanced ductility, while the fine-grained structure and increased precipitate formation in the WZ improved strength but reduced ductility. Aging at 165°C induced notable changes, with precipitate formation causing a 30% reduction in elongation and a 3.6% increase in ultimate tensile strength (UTS), attributed to precipitation hardening and improved bonding. At 175°C, mechanical properties further improved, with a 16% increase in yield strength (YS) and up to a 7.7% rise in UTS. The higher temperature facilitated greater precipitate formation, as confirmed by microstructural analysis, enhancing joint strength. However, this improvement came at the cost of ductility, with a 39.3% reduction in elongation due to restricted dislocation movement caused by the precipitates. Thermal conductivity variations in the welded plates influenced heat distribution and precipitate formation during aging. The process also reduced residual stresses from welding, enhancing diffusion and metallic bonding. Overall, artificial aging improved strength and stiffness but significantly decreased ductility, with aging at 175°C yielding optimal mechanical performance despite the trade-off in ductility.

Abstract: In this study, the bonding of WC-Co cermet to AISI 304L stainless steel was achieved through the flash spark plasma sintering (FSPS) process under a steady pressure of 5 MPa and ultra-short holding durations. The investigation focused on the impact of holding time on interfacial characteristics, diffusion behavior, and mechanical performance. The results demonstrated that prolonged holding times, particularly up to 12 seconds, led to pronounced interfacial deformation and significant diffusion of Co, Ni, and Fe elements across the joint interface. Toughness assessment of the WC-Co cermet near the bonded region was carried out using the Vickers indentation fracture (VIF) technique. The analysis revealed a decline in mechanical integrity with extended holding times, increasing the brittleness of the joint despite the enhanced elemental diffusion between the cermet and the stainless steel.

Abstract: The study investigates the kinetics of plastic deformation propagation in a welded joint of 10G2FB steel after submerged arc welding. A metallographic analysis of the microstructure of the weld seam, fusion zone, and heat-affected zone was performed. Tensile testing and electron microscopy studies were conducted to determine the mechanisms of plastic deformation and crack initiation. It was found that the fusion zone is the most vulnerable to the formation of deformation defects, which can affect the durability of the structure. Recommendations for optimizing welding parameters to improve the mechanical properties of welded joints are proposed.

Abstract: The article considers the features of heat treatment of steels, includes quenching, phase transformations and their influence on the structure and properties of the material. The key parameters of heat treatment are described: heating temperature, holding time and cooling rate, as well as their role in forming the required mechanical characteristics of steel. Phase diagrams are considered, in particular for the "iron-carbon" system, and their significance for choosing processing modes. Additional friction-strain hardening (AFSH) of various steel grades (20, 45, U7, U12) after preliminary quenching and low-temperature tempering is studied. An analysis of microstructural changes and microhardness of surface layers after AFSH is carried out, which confirmed the effectiveness of additional hardening. It was found that steels with a higher carbon content, limited to 0.8 %, demonstrate a greater depth of the hardened layer and higher microhardness values, which determines their feasibility for use in conditions of increased wear. The results of the study emphasize the importance of choosing the optimal AFSH mode depending on the carbon content in the steel, which has a significant impact on the formation of the strength characteristics of the material.

Abstract: High-entropy alloys (HEAs) have garnered significant attention due to their exceptional properties, such as high strength, hardness, corrosion resistance, and excellent formability, which present promising opportunities for energy-related applications. This study successfully synthesized a Ti-doped AlCrFeNiCu high-entropy alloy (HEA) using the laser additive manufacturing (LAM) technique, with potential applications in energy materials. The effects of Ti doping (1 at% and 3 at%) on the mechanical properties and microstructural development of the AlCrFeNiCu HEA were systematically examined. Microstructural analysis using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) identified a dual-phase structure comprising BCC and FCC solid solutions. An Instron universal testing machine and Vickers microhardness (HVN) testing were utilized to evaluate mechanical properties. The findings indicated that although compressive strength diminished with elevated Ti content, Ti enhanced the microhardness of the alloy. The findings indicate the potential applications of Ti-doped AlCrFeNi Cu HEAs in energy sectors, such as components for concentrated solar power systems, nuclear reactors, and advanced gas turbines, which require materials capable of withstanding elevated temperatures, mechanical stress, and corrosive environments. The tailored mechanical and microstructural properties of this HEA position it as a viable candidate for enhancing the longevity and efficiency of energy systems operating under challenging conditions.

Abstract: Mechanical tests and electron microscopic structural studies of low-carbon copper-steels quenched after austenitization and tempered at different temperatures are carried out to clarify the decomposition mechanism of α-Fe based substitution solid solutions. With the onset of decomposition, limited nanosize (4–7 nm) precipitates of so-called ε-phase (solid solution of iron in copper with fcc structure) appear on dislocations. The substructure formed from the austenitic region during quenching determines the nature of such decomposition. In alloys with martensitic structure, the decomposition is heterogeneous. Both the formation of precipitates of the copper-rich ε-phase and their growth primarily occur on dislocations and grain boundaries. In supersaturated alloys with polyhedral ferrite structure, on the contrary, the decomposition is homogeneous, and the growth of the copper-rich phase occurs mainly in the defect-free part of the bcc matrix. Supersaturated iron begins to decompose, forming copper-rich zones isomorphic α-Fe. When a sufficiently high copper concentration is reached, these zones create mechanical stresses that cause local tetragonal distortions of the crystal lattice leading to its reconstruction. When a dislocation loop is formed around this zone, compensating for the elastic deformation, the coherence of the structure is destroyed and fcc precipitates are formed in the matrix. Satisfactory agreement between the theoretical estimate of 8 nm of the critical displacement required for the formation of a dislocation of inconsistency and the initial incoherent precipitates size determined experimentally – by electron microscopy, confirms the proposed mechanism based on the nucleation of nanoinclusions of the ε-phase copper in the bcc iron matrix.

Abstract: Investigating how two different ceramic additives affect the microstructure and nanomechanical characteristics of the Ti6Al4V matrix forms the goal of this work. Under 50 MPa pressure, 10 min dwell time, and 100 °C/min sintering rate at 950 °C, a pulsed electric current sintering process, or PECS, was used. An XRD spectrometer was used to examine the phases, and SEM-EDS was used to examine the bulk morphology of the starting powders and sintered composites. The fabricated Cs1, Cs2, and Cs3 composites attained theoretical densities of 99.74, 98.90, and 96.7%, respectively, above 96.22% of unreinforced Ti-alloy. The SEM analysis showed an even dispersion of the ceramic reinforcements in the matrix of Ti6Al4V, with the characteristics of porous craters in all the samples. Of the three composite samples, Cs1 showed the highest elastic modulus, micro, and nanohardness absolute values of 173 GPa, 796 MPa, and 8942 MPa, respectively, as compared to the unreinforced titanium alloy of 114 GPa, 589 MPa, and 6466 MPa. It was thought that the improved mechanical properties of the sintered composites were due to the production of intermediate phases of Ti₂N and SiO₂ during the sintering process. The materials improvement stands at approximately 30% of the unreinforced Ti-alloy.

Abstract: Hybrid magnets integrate permanent and soft magnetic materials, resulting in enhanced magnetic performance suitable for a variety of applications. Neodymium-iron-boron (NdFeB) magnets, known for their high energy output, exhibit limitations at elevated frequencies due to eddy current effects. To address this problem, it is beneficial to combine NdFeB with high-resistivity nickel zinc ferrites (NZF) to optimize their magnetic properties. This study focuses on the synthesis of NZF and the fabrication of NdFeB/NZF hybrid composites with varying ratios of NdFeB-to-NZF (40:60, 50:50, and 60:40) and different configurations. Their structural, microstructural, and magnetic characteristics were analyzed to identify the optimum fraction for the hybrid composite formulations. In this work, a commercially available NdFeB and NZF were synthesized via high-energy ball milling while NdFeB was used for the composite’s fabrication. Among the synthesized samples, the mixture-composites of a 60:40 ratio exhibited the highest saturation magnetization of 43.01 emu/g with a notable Curie temperature of 390 °C. The results indicate that increasing the hard phase of NdFeB enhances both saturation magnetization and Curie temperature in all composite samples. Conversely, the stacked-composites with a 40:60 ratio displayed the highest resistivity at 7.96x10⁶ Ωm, suggesting that a higher proportion of NZF significantly contributes to increased resistivity. The observed enhancements in magnetic properties can be attributed to the exchange spring mechanism between the soft and hard magnetic phases, as well as the larger grain size in the samples, which promotes a greater number of magnetic domains and reduction of the grain boundaries. Thus, it facilitates more efficient domain wall movement in response to the external magnetic field.