https://repositorio.unifei.edu.br/jspui/handle/123456789/88 2026-04-08T02:41:46Z 2026-04-08T02:41:46Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4355 2026-02-24T14:22:34Z 2025-12-12T00:00:00Z

Desenvolvimento e caracterização de ligas multicomponentes refratárias à base de AlCrNiNbMoW obtidas por metalurgia do pó High-entropy alloys have emerged as a promising alternative for producing materials with exceptional properties. Among these alloys, refractory alloys, comprising refractory elements, stand out for their significant innovation in the development of materials for high-temperature applications. These applications require thermal stability, wear resistance, and oxidation resistance in extreme environments. Composed of five or more principal elements in equiatomic or near-equiatomic proportions, these alloys exhibit high configurational entropy, facilitating the formation of stable solid solutions, in contrast to conventional alloys. Traditionally, these alloys are produced via fusion, a method plagued by economic, environmental, and production drawbacks, as well as heterogeneous structures and elemental segregation. To overcome these challenges, this study proposes the use of powder metallurgy, which fosters the formation of homogeneous alloys with enhanced solubility in the solid state. This approach offers advantages such as minimal waste, rapid production, sustainability, and innovation compared to conventional methods. This investigation examines the influence of varying atomic proportions of Al and Cr on phase formation and oxidation resistance in the refractory alloy AlCrNiNbMoW produced via powder metallurgy. The variation was implemented at 25% increments from the equiatomic proportion to the total replacement of Al by Cr. The results revealed that all alloys achieved densification of up to 95% relative to the theoretical value and exhibited similar microstructures, comprising solid solutions with body-centered cubic (BCC) crystalline structure and Laves phases. Oxidation tests revealed the formation of aluminum, niobium, chromium, and tungsten oxides. The alloy Al4,2Cr29,2Ni16,7Nb16,7Mo16,7W16,7 demonstrated the smallest mass gain (0.037 g/cm²). It was observed that reducing the Al content favors an increase in the fractions of Ni, Mo, and W, and stabilizes Nb in the matrix. The increase in the Cr content had little influence on the oxidation resistance. This study highlights the potential of high-entropy effects in developing novel refractory alloys via powder metallurgy, featuring homogeneous microstructures and optimized properties for high-temperature applications. Tese

2025-12-12T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4354 2026-02-24T13:47:19Z 2024-12-05T00:00:00Z

Avaliação de métodos de união de materiais compósitos termoplásticos This study presents the results of the fabrication of laminated plates of carbon fiber and Elium®150 resin and glass fiber using the Vacuum Assisted Resin Transfer Molding (VARTM) method. It describes the use of material joining techniques, such as bonding and infrared light welding, using this resin for joining composite materials. Elium® resin was thermally characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA). The DSC analysis of the pure resin resulted in a peak curing temperature of 82.92ºC, glass transition temperature (Tg) of 94.16ºC, and curing enthalpy of 216.63 J/g. The DMA results showed a Tg of 50.82ºC for the pure resin, 71.9ºC for the carbon fiber, and 98.47ºC for the glass fiber. TMA results showed a Tg of 91ºC for the carbon fiber and 93ºC for the glass fiber. TGA indicated the onset degradation temperature of 300ºC for both the pure resin and the composites. Ultrasound tests did not detect defects or voids in the glass or carbon laminates. Processing parameters were established using 150, 175, and 200ºC with pressures of 0.4 to 0.5 MPa after the heating phase in the welding process. Shear tests demonstrated higher shear stress values of 14.6 MPa for glass fiber composite samples processed at 150ºC and 0.4 MPa pressure. The glass fiber samples showed better anchorage between the fiber and the matrix due to more effective chemical compatibility. The carbon fiber samples exhibited significant adhesive failures, with the resin detaching from the fiber, indicating insufficient adhesion. This behavior is consistent with the loss of matrix rigidity observed through DMA, particularly at higher welding temperatures. All bonded laminate samples exhibited higher shear strength, with values of 14.68 MPa (carbon fiber) and 16.73 MPa (glass fiber) compared to infrared light-welded samples, which showed maximum values of 14.16 MPa (glass fiber) and 9.91 MPa (carbon fiber). These results support the fact that the bonded samples were processed below the glass transition temperature determined by the DMA technique, thus maintaining their rigidity. Tese

2024-12-05T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4353 2026-02-23T17:46:12Z 2025-08-30T00:00:00Z

Efeito do tempo de moagem de alta energia e da carga de compactação na microestrutura e nas propriedades mecânicas de ligas TI-SI-B produzidas por metalurgia do pó Titanium alloys are widely used in advanced technological applications due to their high specific mechanical strength, low density, and excellent corrosion resistance, making them particularly attractive for the aerospace, biomedical, chemical, and energy sectors. The controlled addition of alloying elements allows tailoring of their properties and significantly expands their range of applications. In this context, silicon (Si) and boron (B) stand out for their pronounced influence on the microstructure and mechanical behavior of titanium, promoting increased hardness, wear resistance, thermal stability, and grain refinement. The combined addition of these elements results in Ti–Si–B alloys with more homogeneous microstructures and superior performance under severe service conditions. The objective of this doctoral research was to investigate the influence of high-energy milling time and compaction load on the microstructure, densification, porosity, and mechanical properties of Ti-2Si-1B and Ti-6Si-3B alloys produced by powder metallurgy. The alloys were synthesized from elemental titanium, silicon, and boron powders processed by high-energy milling in a planetary mill at a rotational speed of 200 rpm, using a ball-to-powder mass ratio of 1:20 and milling times of 4 and 8 hours to promote homogeneous mixing. After milling, the powders were compacted under different loads and sintered at 1250 °C for 4 hours, a condition established based on differential thermal and thermogravimetric analyses, which indicated the occurrence of the main microstructural transformations within this temperature range. Material characterization was performed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, particle size analysis, density and porosity measurements by the Archimedes method, Vickers microhardness testing, nanoindentation for elastic modulus determination, and wettability tests. The results showed that after 4 hours of high-energy milling, both alloys exhibited a predominantly unimodal particle size distribution, with a higher concentration around 50 μm, indicating that mechanical mixing was the dominant mechanism during this processing stage. For the Ti-6Si-3B alloy, the higher content of secondary elements led to a narrower particle size distribution, demonstrating increased milling efficiency. Increasing the milling time to 8 hours resulted in a tendency toward particle agglomeration and broader size distributions, attributed to the high fraction of ductile titanium combined with the high energy input, which favored cold welding. X-ray diffraction analyses revealed the predominance of the α-Ti phase after milling and the formation of intermetallic phases such as Ti₆Si₂B and TiB after sintering, with TiB being more pronounced in the Ti-6Si-3B alloy. The sintered densities ranged from approximately 3.37 to 3.94 g/cm³, with apparent porosity between 11% and 24%. Mechanical testing indicated microhardness values between 400 and 720 HV and elastic moduli consistent with values reported in the literature. Overall, the results demonstrate that low-alloy Ti–Si–B systems produced by high-energy milling and powder metallurgy exhibit homogeneous microstructures and mechanical properties suitable for applications in severe environments, highlighting the importance of careful control of processing parameters. Tese

2025-08-30T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4352 2026-02-23T17:49:00Z 2025-12-10T00:00:00Z

Caracterização de efeitos ambientais no desempenho de células solares bem como sua modelagem e ajustes The growing interest in solar photovoltaic (PV) energy demands a deep understanding of module performance under real operating conditions, which often diverge from standard test conditions. This work presents a robust methodology for characterizing and modeling the electrical behavior of four distinct PV module technologies: multicrystalline silicon (mSi), cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and heterojunction (HIT). The main objective was to investigate the dependence of thermal and irradiance coefficients on photovoltaic modules, so that the models can be employed in future performance estimates of photovoltaic arrays under different climatic conditions, examining the dependence of the five parameters of the single diode model (SDM) as a function of irradiance and temperature. To this end, experimental data from currentvoltage I-V curves and a meta-heuristic optimization algorithm—the Self-Adaptive Differential Evolution (SADE)—were used to extract the model parameters with high precision. The results of the analysis of the temperature coefficients of the electrical parameters reveal significant differences in the thermal behavior of the distinct photovoltaic technologies, reflecting their physical properties and carrier transport and recombination mechanisms. The photogenerated current (𝐼𝑝ℎ) exhibits positive or slightly negative coefficients, indicating a moderate increase in current with temperature, more pronounced in CdTe and mSi and less significant in CIGS. The saturation current (𝐼0) shows strong thermal dependence in all technologies, contributing to the reduction in open-circuit voltage, with greater sensitivity observed in CIGS and mSi. The ideality factor (𝑛) decreases with increasing temperature, with HIT technology being the most affected, indicating more intense changes in recombination mechanisms. Among the resistive parameters, the series resistance (𝑅𝑠) tends to decrease in CdTe and mSi, while it increases in CIGS and HIT, suggesting a greater impact of ohmic losses in these technologies. The shunt resistance (𝑅𝑠ℎ) decreases with temperature in all cases, indicating the intensification of parallel losses, especially in HIT. These results highlight the importance of considering the specific thermal dependence of each technology for more realistic modeling and performance prediction under operating conditions. The irradiance coefficients reveal clear differences in electrical behavior among the photovoltaic technologies. The photogenerated current (𝐼𝑝ℎ) shows the highest sensitivity to irradiance in the HIT module, reflecting its high quantum efficiency and low recombination, while CdTe exhibits the lowest response. The saturation current (𝐼0) shows reduced variations, being more stable in HIT and more sensitive in CdTe and CIGS, associated with higher defect density. The ideality factor (𝑛) decreases with irradiance in CdTe and CIGS, indicating a reduction in non-ideal mechanisms, while it remains practically constant in HIT. The series (𝑅𝑠) and shunt (𝑅𝑠ℎ) resistances tend to decrease with increasing irradiance, with more pronounced variations in mSi and CIGS, whereas HIT shows greater stability, consistent with its heterojunction structure and lower influence of leakage paths. Thus, the proposed methodology, based on precise parameter extraction through the SADE algorithm, proves suitable for capturing such dependencies and provides a consistent basis for more realistic modeling and prediction of the performance of PV modules and arrays under real climatic conditions. The results obtained in this study contribute significantly to the literature by providing specific quantitative data that enhance the accuracy of simulation models. Furthermore, the evidence presented reinforces the potential of the method for improving the design and optimization of photovoltaic systems operating under real climatic conditions. Tese

2025-12-10T00:00:00Z