Materials Science Forum Vol. 1161

Abstract: The development of structural changes at the nanoscale in the austenitic chromium-nickel steels used in the nuclear power industry is studied after Low-Cycle Fatigue (LCF) deformation. The reasons and mechanism of the nanocracks formation due to the structural relaxation in the regions of localized residual internal stresses in slip bands and grain boundaries are discussed. It showed that the locations and distribution of LCF slip bands in the process of microplastic deformation depend on the material’s microstructure.

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: Conventional techniques for obtaining ligatures, ferroalloys, or modifiers are often associated with prolonged processing times, material losses, low energy efficiency, and environmental challenges. The self-propagating high-temperature synthesis (SHS) metallurgy method partially eliminates these drawbacks, allowing ligatures to be formed from hard- and soft-melting elements. The present work focuses on selecting a metallurgical technique for producing SHS complex ligatures in the Fe–Mn–B system, studying the structure and chemical composition of obtained ligatures, and evaluating their corrosion properties.

Abstract: Submerged friction stir processing is a variant of processing metallic materials that is based on the principle of FSW welding and which considers the local modification of the mechanical properties and the microstructure of the material to be processed. By carrying out the underwater SFSP processing, the thermal overload of the material to be processed and that of the processing tool is reduced, thus contributing to the reduction of the dimensions of the heat affected zone and of the deformations of the processed material, as well as to a greater durability of the tool. The paper presents results obtained by ISIM Timisoara regarding the submerged friction stir processing (SFSP) of the EN AW 1200 aluminum alloy with a thickness of 5 mm. The SFSP processing was done in multiple passes using a steel processing tool, with a conical pin with four flat chamfers and different processing parameters. The positive preliminary results are useful for complex experimental research on SFSP processing of aluminum alloys, which will be carried out within the ongoing Nucleu project PN 23 37 01 02.

Abstract: Friction stir processing is a research domain in a continuous dynamic that has led to the development of some variants of its application. One of the variants is submerged friction stir processing to avoid excessive heating of the processing tool and the materials to be processed. The paper presents the results of the experimental research carried out at ISIM Timisoara regarding the submerged friction stir processing (SFSP) of the EN AW 5754 aluminum alloy with a thickness of 3 mm. SFSP processing was performed in one pass and in multiple passes using a processing tool having conical pin with four flat chamfers and different processing parameters. To evaluate the processed material, structural analyses, hardness measurements, as well as mechanical tensile and static bending tests were performed.The preliminary experimental research carried out within the ongoing Nucleu PN 23 37 01 02 project shows favorable results in the SFSP processing of the EN AW 5754 aluminum alloy.

Abstract: This paper provides an analysis of the fracture surface of aluminum alloy EN AW 6082 Submerged Friction Stir Processed. Processing was performed in multiple passes. The specimens taken from the material processed for the tensile failure test were also analyzed from the point of view of the failure surfaces. The investigation of these surfaces involved microscopic analyzes carried out with the help of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques, to study the microstructure, fracture surfaces and constituent elements of the analyzed area. Based on the conclusions obtained from the analysis of the fracture surface of the aluminum alloy EN AW 6082 Submerged Friction Stir Processed, recommendations can be made to improve the quality and reliability of the alloy. The results of this research contribute to the development of knowledge on Submerged Friction Stir Processed of aluminum alloy EN AW 6082.

Abstract: The study examines the effects of the Friction Stir Processing (FSP) process on the EN AW 5754 aluminium alloy, conducted under underwater conditions. FSP is an innovative technology used to improve the mechanical properties of materials through plastic deformation. Fracture surface analysis is essential for understanding how the process influences the internal structure of the alloy and its behaviour during fracture. The results obtained from the fracture analysis provide insights into the deformation mechanisms and how processing conditions affect the material's structural integrity. This study contributes to the development of aluminium alloys with enhanced properties, with applications in fields such as the automotive and aerospace industries.

Abstract: This article describes the development and characterization of a curcumin-loaded alginate-xanthan gum hydrogel, designed to provide both antibacterial activity and controlled drug release.The hydrogel formulation consisted of 4% (w/v) alginate, 4% (w/v) xanthan gum, and 500 μg/mL of curcumin. Sterilization was achieved through ethanol immersion, UV irradiation, and autoclaving, with the latter two methods proving to be the most effective in maintaining long-term sterility. Antibacterial efficacy was tested against Staphylococcus aureus, demonstrating a significant inhibition zone around the hydrogel. The curcumin release profile indicated a sustained release over 72 hours, suggesting its suitability for prolonged antibacterial applications.

Abstract: This study aimed to develop microcapsules of rose oil (RO)-β-cyclodextrin and rose extract (RE)-β-cyclodextrin using an optimized co-precipitation method. RO and RE were obtained via solvent-free microwave extraction (SFME), yielding 0.25% and 6.36%, respectively. The antioxidant activities and total phenolic contents of RO and RE were analyzed before microencapsulation. Results showed that RO and RE had IC₅₀ antioxidant values of 6.22 µg/mL and 5.13 µg/mL, compared to Trolox at 4.67 µg/mL. Additionally, the total phenolic contents of RO and RE were found to be 215.46 ± 0.4 and 441.23 ± 1.2 mg GAE/g extract, respectively. The influence of varying ethanol concentrations (20%, 30%, 40%, and 50% v/v) on encapsulation efficiency was thoroughly investigated. Using β-cyclodextrin as the encapsulating agent, a 40% ethanol concentration provided high encapsulation efficiencies, with microcapsule recovery rates of 84.23% and 81.55%, and encapsulation efficiencies of 72.36% and 71.26% for RO and RE, respectively. Characterization of β-cyclodextrin inclusion complexes of RO and RE through scanning electron microscopy (SEM), fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermal analysis (DSC, TGA) revealed significant changes in FTIR spectra, XRD, SEM and thermal analysis, indicating complexations of β-cyclodextrin with RO and RE. Antioxidant activities and total phenolic contents of the optimized microcapsules, prepared using 40% ethanol concentration, were assessed after storage of microcapsules for 1 month, showing that the microcapsules effectively stabilized RO and RE over time. These findings suggest that RO and RE inclusion complexes with β-cyclodextrin could be promising bioactive materials for developing functional foods, beverages, and cosmetics.