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The objective underlined in this work is to apply Rotary Friction Welding (RFW) process to joint similar AA2024 and TiAl6V4 welds. The experiment is conducted by varying the input parameters (rotational speed, friction pressure and friction time) using Taguchi’s L9 orthogonal array method. MINITAB software was used to plot the response chart. The output parameter considered in this approach is the Ultimate Tensile Strength (UTS) of the weld joint, where the optimum RFW condition for maximizing the UTS were determined. Besides, the most influential process parameter has been determined using statistical analysis of variance (ANOVA). Finally, the general regression equations of the UTS for both materials are formulated and confirmed by means of the experimental tests values.

The aim of this work is to investigate the effect of normal pressure upon the mechanical properties and their related microstructures of the similar Ti-6Al-4V and AA2024 Rotary Friction Welding (RFW) joints. The main characteristic of this process is the use of friction to generate adequate energy and raise temperature locally in order to create favorable conditions for welding at the interface between two parts. Successful welds were produced showing, among many others, that the fracture occurres at the weld interface for the AA2024 alloy, hence its low tensile strength. However, the fracture occurres outside the weld interface for the Ti-6Al-4V alloy, which indicates that the weld joint is more resistant than the base metal. The microscopic observation of the fracture surfaces of the AA2024 samples exhibits a mixture of morphologies with a majority of rough cupular surfaces, indicating a dominant ductile fracture mode. For the Ti-6Al-4V RFW joints, cupules of different sizes are observed over the entire surface that also exhibits a ductile fracture mode.

This study evaluates Algerian kaolin (Djebel Debbagh (DD1) and Tamazart (KT2)) as potential substitutes for commercial kaolin (Lab) in the production of mullite‐based ceramics. Three compositions were prepared by incorporating the appropriate percentage of alumina to each calcined kaolin to achieve stoichiometric mullite precursors. The phase evolution of individual kaolin powders, as well as their mixtures with alumina, depends strongly on the calcination temperature and kaolin impurities. The differential scanning calorimetry combined with thermogravimetric analysis (TGA) showed lower secondary mullite formation temperature for the KT2‐based mixture. However, X‐ray diffraction revealed a complete mullitization in DD1 mixture. The K2O hindered cristobalite formation and reduced secondary mullite formation rate. Microstructure analysis showed lath‐shaped primary mullite and equi‐axed secondary mullite particles. After sintering at 1600°C, The KT2‐based sample (M3) exhibited higher density (3.013 g/cm3) and hardness (9.9 GPa), whereas the DD2‐based sample (M2) showed moderate densification (2.91 g/cm3) and higher flexural strength (159.42 MPa). Impurities (mainly Fe2O3, and K2O) promoted liquid phase sintering, resulting in greater densification in M3, whereas M2 showed more homogeneous microstructure, refined grains, and lower glassy phase content, contributing to enhanced strength. [ABSTRACT FROM AUTHOR]

The focus of this study is to investigate the impact of cyclic loading path and temperature on the mechanical behavior of AA2024 aluminum alloy, a material commonly used in the aerospace industry. Our study aims to understand the cyclic evolution of work hardening (isotropic and kinematic) in response to different loading paths: tension‐compression cycles followed by equivalent torsion cycles, and vice versa. We also perform microstructural investigations using a scanning electron microscope (SEM) to gain insights into the evolution of fatigue damage during cyclic loading. By examining these factors, we aim to provide insights into the material's mechanical behavior and anisotropy. This research contributes to improving our understanding of the performance of AA2024 alloy under cyclic loading conditions. Highlights: Cyclic hardening of AA2024 alloy is affected by loading path and temperature.Alloy exhibits hardening behavior under axial and shear loading, with cyclic stabilityInverted loading paths lead to discontinuity in behavior: axial loading followed by alternating torsion causes softening, vice versa to hardening.SEM microstructural analysis reveals fatigue damage evolution during cyclic loading, relevant for aerospace industry and aircraft structure fatigue life prediction. [ABSTRACT FROM AUTHOR]

The valves of an internal combustion engine play an essential role in the automobiles and their surroundings significantly affect their thermo-mechanical behavior. The work aims to assess numerically the effect of the real thermo-mechanical boundary conditions on the valves by considering the actual complex surrounding. For this purpose, we have subdivided the valve into seven adequate zones. We have evaluated the average values of the transient heat transfer coefficient, the adiabatic wall temperature and the mechanical load at each subdivision are during the opening and the closing periods. A transient Finite Element Model under ANSYS APDL software is developed and simulations are carried out until reaching the steady state. The temperature distribution and the thermal stresses at each valve position is obtained and then analyzed. The main findings show that the stress intensity distribution is developed in the zones labelled stem guide port and seat local of large temperature gradients, which causes high thermal stresses responsible of cracks or thermal fatigue damage. In addition, knowing the temperature map, the thermal gradient and stress under actual conditions will surely help manufacturers to better design exhaust valve, avoid early failure and enhance the durability of valves. [ABSTRACT FROM AUTHOR]

The multiferroic ceramics Bi 0. 8 Ba 0. 2 Fe 1 − x SbxO3 with x = 0 , 0.01, and 0.02 were synthesized using the solid-phase reaction technique. The samples were sintered at two different temperatures, 850∘C and 900∘C. Scanning electron microscopy revealed the effect of antimony concentration on grain size and formation. The effect of Sb-doping on the crystal structure and ferroelectric properties of these ceramics was investigated using X-ray diffraction, Raman spectroscopy, and dielectric measurements. The dielectric constant was enhanced upon Fe 3 + substitution by Sb 3 + without affecting the dielectric loss of the ceramics. The tetragonal distortion of the rhombohedral symmetry of BiFeO3 caused by Ba-doping at Bi 3 + site was lifted by Sb-doping at Fe 3 + site. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this Note is the study of the structure and fluxional behavior of the complex [{Ru(CO)2(η5C5H5)}3(η1:η1:η2:-CC)]+, using density functional methods. The molecular geometry of this complex will be optimized, the transition state (TS) of the fluxional process will be determined and the origin of the energy barrier will be analyzed. [Copyright &y& Elsevier]

The nature of the chemical metal-metal bond in M 2 (CO) 10 (M = Mn, Re, Tc) dinuclear decacarbonyls complexes was investigated for the first time using the natural orbital chemical valence (NOCV) approach combined with the extended transition state (ETS) for energy decomposition analysis (EDA). The optimized geometries carried out at different levels of theory BP86, BLYP, BLYPD and BP86D, showed that the latter method, i.e., BP86D, led to the best agreement with X-ray experimental measurements. The BP86D/TZP results revealed that the computed covalent contribution to the metal-metal bond are 60.5%, 54.1% and 52.0% for Mn-Mn, Re-Re and Tc-Tc, respectively. The computed total interaction energies resulting from attractive terms (ΔE orb and ΔE eles ), correspond well to experimental predictions, based on bond lengths and energy interaction analysis for the studied complexes.