Avaliação da dureza do aço ASTM A182-P22 após simulação física do processo de soldagem por atrito de pino não consumível quando submetido a diferentes ciclos térmicos

O processo de soldagem por atrito de pino não consumível (SAPNC), devido as suas vantagens perante a soldagem convencional, tem sido desenvolvido em diversas partes pelo mundo. Quando se trata de aços, o processo devenvolve um comportamento semelhante ao da têmpera, ocasionando em uma microestrura com morfologia de martensíta bruta, assim o material apresenta elevada dureza e baixa tenacidade à fratura, condições que podem fazer com que o material não se torne interessante para diversas aplicações industriais. O presente trabalho, tem como objetivo estudar o comportamento da dureza do aço ASTM A182 P 22 submetido à diferentes ciclos térmicos. Para tanto, estuda-se a possibilidade de reduzir a dureza do material de trabalho através do emprego de uma bobina indutora para proporcionar modificações no comportamento térmico do processo. Com o estudo realizado, percebe-se que alterar as taxas de resfriamento não causa mudança significativa na dureza do material, contudo, quando a bobina indutora é utilizada realizando revenimento à 720 °C, há modificações significativas nesta propriedade do material mesmo que os tempos de revenimento sejam pequenos.The Friction Stir Welding (FSW), due to its advantages over conventional welding process, has been developed in several parts of the world. When it comes to steel, the process develops a behavior similar to that of quenching, resulting in a microstructure with morphology of brute martensite. Therefore, the material presents high hardness and low fracture toughness, conditions that may cause the material not to become interesting for various industrial applications. The present work aims to study the hardness behavior of ASTM A182 P 22 steel subjected to different thermal cycles. For this, it is studied the possibility of reducing the hardness of the working material through the usage of an inductive coil to provide modifications in the thermal behavior. With the study carried out, it is noticed that changing the cooling rates does not cause a significant change in the hardness of the material, however, when the induction coil is used by tempering the material at 720°C, there are significant modifications in the property of the material, even though the process\u27s time is small

Synthesis, characterization and photocatalytic activity of nanostructured oxides of (Ti-Fe-O) obtained by high energy ball milling

Orientadores: Rodnei Bertazzoli, Nathália Carolina VeríssimoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A proposta geral desta dissertação de mestrado consiste em investigar o comportamento fotocatalítico de fotoanodos para aplicação de fotoeletrólise da água (`water-splitting¿). Tais eletrodos foram obtidos através de heterojunções de óxidos semicondutores obtidos partir da sinterização de nanopartículas metálicas produzidas pelo processo de moagem por alta energia. Para esse fim, duas ligas metálicas (Ti - 40wt.%Fe e Fe22 - wt.%Ti) foram elaboradas primeiramente por fusão a arco e depois submetidas ao processo de moagem pelo período de nove horas, no qual a solução de 10 mL de H2O D.I, 1 mL de ácido oleico, 1 mL de solução de PEG 25% foi adicionada exercendo o papel de surfactante. A morfologia, o refinamento e as estruturas cristalinas do material obtido do processo de moagem foram caracterizados por Microscopia Eletrônica de Varredura, Microscopia Eletrônica de Transmissão e Difração de Raios-X. Os resultados experimentais demonstraram que o processo resultou em dois conjuntos de partículas, sendo uma delas nanopartículas esféricas unitárias com tamanho médio de 2- 6 nm e a outra se caracteriza por aglomerados com morfologia arredondada com tamanho médio de 0,6 ?m os quais são decorados por nanopartículas. Foi observado que na composição com maior porcentual de ferro, o processo de moagem resultou em menores tamanhos de partícula. O material obtido foi depositado sobre substrato condutor (TCO) e tratado termicamente a de 600 °C e 850 °C. As técnicas de difração de raio-x e espectroscopia Raman demonstraram que as duas composições com tratamento térmico a 600 ºC, resultou nas fases cristalinas rutilo e a hematita. Entretanto, para a temperatura de 850 ºC as duas ligas se comportaram de maneira diferenciada. Enquanto a liga Ti ¿ 40wt.%Fe resultou na formação dos óxidos pseudobrooquita e rutilo, a liga Fe - 22wt.%Ti houve conversão das partículas metálicas em hematita, rutilo e pseudobrookita. O desempenho fotoeletroquímico foi avaliado em eletrólito de 1M de NaOH e 1M de NaOH + 0,5 M H2O2 como hole scavenger. As fotocorrentes foram obtidas sob iluminação utilizando-se de um simulador solar de lâmpada de Xe de 150 W e filtro de 1,5 AM. Observou-se que para as duas composições, a temperatura de 600 °C resultou nos melhores resultados de densidade de corrente (0,45 e 0,40 mA.cm -2 V vs.RHE para Ti - 40wt.% Fe e Fe - 22wt.% Ti, respectivamente), enquanto que na temperatura de 850 °C tiveram o desempenho de 0,051 e 0,025mA.cm -2 V vs. RHE para Ti - 40wt.% Fe e Fe - 22wt.% TiAbstract: The general proposal of this master's degree dissertation consists in investigating the photocatalytic behavior of photoanodes for the application in water splitting process. These electrodes were obtained through semiconductor oxide heterojunctions, obtained from the sintering of metallic nanoparticles produced by high energy ball milling process. For this purpose, two metallic alloys (Ti - 40wt.%Fe and Fe ¿ 22wt.%Ti) were elaborated first by arc melting and then subjected to the grinding process for a period of nine hours, in which a solution (10 mL of H2O DI, 1 mL of oleic acid and 1 mL of 25% PEG) was added as a surfactant role. The morphology, refinement and crystalline structures of the processing material of the grinding process were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy and X-Ray Diffraction. The experimental results showed that the process resulted in two sets of particles, one of which is spherical unitary nanoparticles with an average size of 2-6 nm and the other stands out for clusters with rounded morphology with and average size of 0.6 ?m which are decorated by nanoparticles. It was observed that in the composition with the highest percentage of iron, the grinding process resulted in smaller particles sizes. The material was deposited on ad conductive substrate (TCO) and heat treated at 600 °C and 850 °C. The X-Ray diffraction and Raman spectroscopy techniques demonstrated that the two compositions with heat treatment at 600 °C resulted in the crystalline phases of rutile and hematite. However, for the temperature of 850 °C, the two alloys behaved differently. While the Ti - 40wt.%Fe alloy resulted in the formation of pseudobrookite and rutile oxides, the metallic particles from the Fe ¿ 22wt.% Ti alloy were converted into hematite, rutile and pseudobrookite. The photoelectrochemical performance was evaluated in the electrolyte of 1M NaOH and 1M NaOH + 0.5 M H2O2 as a hole scavenger. The photocurrents were obtained under illumination by a 150 W Xe lamp simulator and 1.5 AM filter. It was observed that for both compositions, that the temperature of 600 °C resulted in the best results of current density (0.45 and 0.40 mA.cm-2 vs.RHE for Ti - 40wt.% Ti and Fe - 22wt.%Ti, respectively), while at 850 °C it had the performance of 0,051 and 0,025 mA.cm-2 vs.RHE for Ti - 40wt.% Ti and Fe - 22wt%.TiMestradoMateriais e Processos de FabricaçãoMestra em Engenharia Mecânic

Arc Synthesis, Crystal Structure, and Photoelectrochemistry of Copper(I) Tungstate

A little-studied p-type ternary oxide semiconductor, copper(I) tungstate (Cu2WO4), was assessed by a combined theoretical/experimental approach. A detailed computational study was performed to solve the long-standing debate on the space group of Cu2WO4, which was determined to be triclinic P1. Cu2WO4 was synthesized by a time-efficient, arc-melting method, and the crystalline reddish particulate product showed broad-band absorption in the UV–visible spectral region, thermal stability up to ∼260 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu(I) to Cu(II) oxidation state showed that the crystal lattice could accommodate Cu2+ cations up to ∼260 °C, beyond which the compound was converted to CuO and CuWO4. This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The electronic band structure of Cu2WO4 was contrasted with that of the Cu(II) counterpart, CuWO4 using spin-polarized density functional theory (DFT). Finally, the compound Cu2WO4 was determined to have a high-lying (negative potential) conduction band edge underlining its promise for driving energetic photoredox reactions

Arc Synthesis, Crystal Structure, and Photoelectrochemistry of Copper(I) Tungstate

A little-studied p-type ternary oxide semiconductor, copper(I) tungstate (Cu2WO4), was assessed by a combined theoretical/experimental approach. A detailed computational study was performed to solve the long-standing debate on the space group of Cu2WO4, which was determined to be triclinic P1. Cu2WO4 was synthesized by a time-efficient, arc-melting method, and the crystalline reddish particulate product showed broad-band absorption in the UV–visible spectral region, thermal stability up to ∼260 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu(I) to Cu(II) oxidation state showed that the crystal lattice could accommodate Cu2+ cations up to ∼260 °C, beyond which the compound was converted to CuO and CuWO4. This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The electronic band structure of Cu2WO4 was contrasted with that of the Cu(II) counterpart, CuWO4 using spin-polarized density functional theory (DFT). Finally, the compound Cu2WO4 was determined to have a high-lying (negative potential) conduction band edge underlining its promise for driving energetic photoredox reactions