In this study, cellular spacing, porosity and corrosion of 1050 aluminum alloy subjected to the different levels of Gamma radiation was examined using a Gammacell Co-60 type irradiator, with activity of 16.13 TBq and dose rate around 6.98 Gy/min. Samples were extracted from an aluminum ingot, which was obtained with directional solidification apparatus. This upward directional solidification technique allowed obtaining of aluminum samples under different conditions of cooling rates. Firstly, cooling rates were determined during solidification experiment and then correlated to the cellular spacings and porosity content. The experimental results pointed out that cooling rates exerts a strong effect on the microstructural patterns and porosity formation. Laws have been determined, indicating that increase in cooling rates favored a refinement effect on as-cast microstructure and a decrease in porosity content. Furthermore, measurable effects of different levels of the Gamma radiation on the microstructure, porosity and corrosion for samples of 1050 aluminum alloy, were determined. The experimental results show that Gamma radiation has favored changes in cellular spacings, porosity formation and corrosion behavior. From this results, one can conclude that coarser microstructures, porosity formation and corrosion are favored by prolonged thermal annealing caused by temperature field generated during Gamma radiation exposure. On the other hand, even after the exposure to different levels of Gamma radiation, the microstructure and porosity observed in as-cast samples are still strongly dependent of the cooling conditions. study spacing 105 Co60 Co 60 Co-6 irradiator 1613 16 13 16.1 698 6 98 6.9 Gymin Gy min Gy/min ingot apparatus Firstly content ascast as cast Furthermore behavior microstructures hand 10 Co6 Co- 161 1 16. 69 9 6.

Resumo A soldagem dissimilar (Dissimilar Metal Welds – DMWs), união de dois diferentes materiais metálicos, tem muitas aplicações industriais, com destaque para trocadores de calor nas usinas nucleares. Portanto, devem resistir à corrosão e a esforços mecânicos, entre outros requisitos. Neste trabalho foi abordada a susceptibilidade à corrosão da junta de união (feita por soldagem TIG – Tungsten Inert Gas), de forma autógena, de dois materiais distintos: Inconel 718 e o aço AISI 316L. Foram realizadas soldagens sob diferentes condições de aportes térmicos e correspondentes quantificações de fases utilizando microscopias e ferritoscopia e correlacionadas com o comportamento eletroquímico desta união em meios contendo cloretos. As análises microscópicas e ferromagnéticas mostraram que não houve formação da fase sigma durante a soldagem e a existência de altos teores de ferrita na região da zona fundida próxima a ZAC (zona afetada pelo calor) do aço 316L. Os ensaios eletroquímicos de corrosão mostram que as amostras nas diferentes regiões apresentaram a seguinte ordem decrescente de resistência à corrosão localizada: Amostra com maior aporte térmico (0,50 J/mm), na interface ZF/Inconel > Amostra com menor aporte térmico (0,33 J/mm) na interface ZF/Inconel > Amostra com menor aporte térmico, na interface ZF/316L > Amostra com maior aporte térmico, na interface ZF/316L> aço 316L. Finalmente, os diferentes aportes térmicos não provocaram diminuição da resistência à corrosão comparados ao aço 316L nas diferentes regiões de solda.

Abstract Dissimilar Metal Welds (DMWs) union of two different metallic materials has many industrial applications, with emphasis for heat exchangers in nuclear power plants. Therefore, they must have enhanced corrosion and mechanical stress resistances, among other properties. The focus of this work is the analysis of the susceptibility to corrosion of the joint (made by TIG welding – Tungsten Inert Gas) of two different materials: Inconel 718 and AISI 316L stainless steel, without filler metal. Micrographic and ferroscopy analyses were performed for different heat input conditions and correlated with the electrochemical behavior of this joint in an environment containing chlorides. The metallographic and ferroscopy analyses did not reveal sigma phase formation during welding and showed high ferrite content in the region of the fusion zone near the HAZ (heat affected zone) of the 316L. The electrochemical corrosion tests showed that the samples in the different regions presented the following decreasing order of localized corrosion resistance: Sample with higher heat input (0.50 J / mm), at the interface ZF / Inconel > Sample with lower heat input (0.33 J / mm) at the interface ZF / Inconel > Sample with lower heat input, at interface ZF / 316L > Sample with higher heat input at interface ZF / 316L > 316L . Finally, the different heat inputs did not cause a significant decrease in the corrosion resistance in the different regions of the weld in relation to 316L.

Measurements at high temperature using liquid solutions require special cells and materials which are able to support the temperature and pressure developed inside. The constructed cell was designed to support pressures up to 20 bar, temperatures relatively high up to around 200 ºC, depending on the pressure developed inside the system. It also supports aggressive solutions since its inner wall is made of Teflon. The electrolyte has no contact with the metallic body of the cell. Then, it is supposed that this work represents a great contribution to the electrochemical studies of materials in solutions at high pressure and temperature