The precipitation kinetics in a Cu-4 mass% Ti alloy was studied using SEM, TEM, XRD and Vickers hardness. A Cu-4 mass% Ti alloy was prepared, homogenized, solution treated and then aged at 673, 773 and 873 K for times between 0.6 to 720 ks. The XRD and TEM results indicated that the phase decomposition occurred by spinodal decomposition during the early stages of aging. The growth kinetics of composition modulation wavelength is very slow at the early stages of aging. The precipitation of metaestable 0 (Cu 4 Ti) preceded to that of the equilibrium phase phase (Cu 3 Ti), which formed through cellular precipitation. The coarsening process of 0 phase followed the LSW theory for diffusioncontrolled growth. The activation energy for this coarsening process was determined to be about 190 AE 10 kJÁmol À1 . The discontinuous precipitation of phase has an activation energy of about 207 kJÁmol À1 and an exponent time of about one. The highest hardness and fastest transformation kinetics occurred at aging temperatures of 673 and 873 K, respectively.
A novel medium-Mn steel microstructure with 0.1 wt.% Nb was designed using Thermo-Calc and JMatPro thermodynamic simulation software. The pseudo-binary equilibrium phase diagram and time–temperature transformation (TTT) and continuous cooling transformation (CCT) diagrams were simulated in order to analyze the evolution of equilibrium phases during solidification and homogenization heat treatment. Subsequently, the steel was cast in a vacuum induction furnace with the composition selected from simulations. The specimens were heat-treated at 1200 °C and water-quenched. The results of the simulations were compared to the experimental results. The microstructure was characterized using optical microscopy (OM) and scanning electron microscopy (SEM). We found that the as-cast microstructure consisted mainly of a mixture of martensite, ferrite, and a low amount of austenite, while the microstructure in the homogenization condition corresponded to martensite and retained austenite, which was verified by X-ray diffraction tests. In order to design further production stages of the steel, the homogenized samples were subjected to hot compression testing to determine their plastic flow behavior, employing deformation rates of 0.083 and 0.83 s−1, and temperatures of 800 and 950 °C.
Computational simulation has become more important in the design of thermomechanical processing since it allows the optimization of associated parameters such as temperature, stresses, strains and phase transformations. This work presents the results of the three-dimensional Finite Element Method (FEM) simulation of the hot rolling process of a medium Mn steel using DEFORM-3D software. Temperature and effective strain distribution in the surface and center of the sheet were analyzed for different rolling passes; also the change in damage factor was evaluated. According to the hot rolling simulation results, experimental hot rolling parameters were established in order to obtain the desired microstructure avoiding the presence of ferrite precipitation during the process. The microstructural characterization of the hot rolled steel was carried out using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the phases present in the steel after hot rolling are austenite and α′-martensite. Additionally, to understand the mechanical behavior, tensile tests were performed and concluded that this new steel can be catalogued in the third automotive generation.
In this work, we propose an easy and a low cost method for the synthesis of Nitrogen-Doped Graphene NDG and its silver nanowires NW functionalization NWGN. The synthesis was performed using the improved graphene oxide method, chemical reduction of graphene oxide in the presence of caffeine as green nitrogen source and the subsequently the silver nanowires growth in the surface, by the chemical reductions salts in the presence of NG. Achieving a homogeneous growing (coating) of graphene sheets. The samples were analyzed using conventional characterization techniques: SEM-EDX, XRD, FT-IR, RAMAN, TEM, HRTEM, STEM and XPS.
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