Estudo do efeito da adição de zircônia na microestrutura e propriedades do aço EUROFER sinterizado
The EUROFER is an alloy steel developed for application in nuclear reactor, with mechanical properties compatible with such a use, since the operating temperature does not exceed 550°C due to its low creep resistance. In order to improve the mechanical properties of EUROFER, studies have been develo...
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| Formato: | Dissertação |
| Idioma: | por |
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/22251 |
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| Resumo: | The EUROFER is an alloy steel developed for application in nuclear reactor, with mechanical properties compatible with such a use, since the operating temperature does not exceed 550°C due to its low creep resistance. In order to improve the mechanical properties of EUROFER, studies have been developed by adding yttria, producing a composite with higher working temperature of approximately 650°C. In this work, we studied the effect of adding zirconia and sintering atmosphere on microstructure and mechanical properties of EUROFER steel processed through the steps of powder metallurgy. Initially, wt % zirconia was added to steel and high energy ball milling was performed in a planetary milling for 5 hours at 400rpm. Then the particles were annealed in a resistance vacuum furnace at 950°C for 30 minutes for better compression. The pure EUROFER powder and EUROFER with 5 wt% zirconia cold compacted under a uniaxial double-acting pressure of 700 MPa in a cylindrical metal matrix with a cavity of 5 mm in diameter. The green samples were sintered in resistance vacuum furnace and resistance furnace with argon flow at 1300 °C for 60 minutes with a heating rate of 10 °C / min. Primary and milled powders were characterized by particle size distribution analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD) with refinement, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). And the sintered samples were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS); and also analyzed by density measurement, dilatometry behavior and microhardness. It was observed that the initial microstructure of EUROFER did not maintain during processing of the material, and, therefore, its mechanical properties presented variations. Thus, the results of microhardness obtained for samples with zirconia (argon flow 253,4 HV and vacuum 119,35 HV) were higher than those of sintered pure steel (argon flow and vacuum 119,25HV 84,65HV) . Thus, the results of microhardness obtained for samples with added zirconia (argon flow and vacuum 253,4HV 119,35HV) were higher than those of sintered pure steel (argon flow 119,25 HV and vacuum 84,65 HV). Besides, the samples sintered in the resistance furnace under argon flow had higher hardness than samples sintered in vacuum resistance furnace. |
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