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CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Magnesium is the lightest structural metal with a high strength-to-mass ratio, offering considerable potential for automotive and aerospace applications. However, its use remains restricted due to its poor formability at room temperature and low strength. To improve the properties of Mg, some of the viable alternatives are alloying with rare-earth elements and subjecting the material to severe plastic deformation. The present work investigated the microstructural and mechanical evolution of a Mg-1wt% Mn-1wt%Nd processed by high-pressure torsion, and its microstructure was characterized by X-ray diffraction, scanning, and transmission electron microscopy. The segregation of alloying elements was observed with high-angular annular dark-field images, and it is typically related to higher hardness and thermal stability, enhancing the interest in understanding their formation. The results show that Nd readily segregates to grain boundaries in early stages of deformation, while Mn, which was dispersed as small particles in the starting material, undergoes slow fragmentation forming nanoparticles distributed throughout the microstructure, and segregates to boundaries in a distinctly more sluggish manner than Nd atoms. The evolution of microhardness shows a rapid increase in strength at low imposed strains until reaching saturation. It is suggested that Mn plays only a minor role in the contribution to the strength of this alloy because the slow development of nanoclusters and segregations of this element does not relevantly affect the hardness. O magnésio é o metal estrutural mais leve, apresentando uma alta resistência específica e oferecendo um considerável potencial para aplicações automotivas e aeroespaciais. No entanto, o seu uso permanece restrito devido a sua baixa formabilidade à temperatura ambiente e a sua baixa resistência mecânica. Para melhorar as propriedades do Mg, algumas das alternativas viáveis são adicionar elementos terras-raras às suas ligas e submeter o material à deformação plástica severa. O presente trabalho investiga a evolução microestrutural e mecânica da liga Mg-1%Mn-1%Nd em peso processada por torção sob alta pressão, e a microestrutura foi caracterizada por difração de raios X, microscopia eletrônica de varredura e de transmissão. A segregação dos elementos de liga foi avaliada com imagens de campo escuro de alto ângulo, e é tipicamente relacionada a uma maior dureza e estabilidade térmica, o que aumenta o interesse em entender sua formação. Os resultados mostram que o Nd segrega rapidamente para os contornos de grão nos estágios iniciais de deformação, enquanto o Mn, que estava disperso em pequenas partículas no material inicial, sofre uma fragmentação lenta, formando nanopartículas distribuídas por toda a microestrutura e segregando para os contornos de uma maneira distintamente mais lenta do que os átomos de Nd. A evolução da microdureza mostra um rápido aumento da resistência mecânica para níveis baixos de deformação, até a sua saturação. Sugere-se que o Mn desempenhe um papel com pouca relevância na contribuição para o aumento de resistência dessa liga, pois o lento desenvolvimento de nano-aglomerados e segregações desse elemento não afeta de forma relevante a dureza.

The nondestructive nature of X-ray microtomography (µCT) associated with its suitable temporal resolution, obtained with the use of high energy polychromatic radiation from electron acceleration rings, allows in situ investigations of the damage evolution process during tensile loading in composite materials. In this context, the development of adequate scientific instrumentation as well as the understanding of the corresponding technology by research groups is paramount to guarantee reliability of the obtained results. In the present work, a miniaturized universal testing machine (tensile, compression and fatigue) was developed to be applied in in situ µCT experiments using synchrotron radiation with innovative technology. The equipment has a uniaxial load capacity of up to 300 N with 1 N resolution and can impose 0.01 mm resolution displacements following controlled deformation rates. In order to validate the developed equipment, tensile test results performed on sub-sized and standard annealed copper specimens were compared and in situ µCT tensile tests were performed in glass-fiber-reinforced polypropylene matrix composites at the Laboratorio Nacional de Luz Sincrotron (LNLS) in Campinas (SP, Brazil). Data analysis was performed by applying image processing techniques to successive tomograms in order to monitor crack propagation in the initial stages of damage evolution. The results obtained allowed the clarification of crack propagation mechanisms in the investigated composite materials and demonstrated the viability of the equipment’s intended application.

The present work evaluates the segregation of alloying elements during severe plastic deformation of a magnesium alloy. A Mg-1wt% Mn-1wt% Nd alloy was processed by high-pressure torsion and the microstructure was characterized by X-ray diffraction, scanning and transmission electron microscopy. High angular annular dark-field images were used to distinguish areas with segregated alloying elements. The results show that Nd readily segregates along boundaries in the early stage of deformation while Mn, which was dispersed as small particles in the starting material, undergoes slow fragmentation forming nanoparticles distributed throughout the microstructure and segregates along boundaries. The evolution of microhardness shows a rapid increase in strength at low imposed strains and saturates. It is suggested that Mn plays only a minor role in the contribution to the strength of this alloy because the slow development of nano-clusters and segregations of this element is not accompanied by changes in hardness.

Carbonate and sandstone reservoirs play an important role in oil industry as they host over 50% of the world’s hydrocarbon reserves. For an accurately assessment of porosity and pore size distribution of such complex pore-network, which affect directly the macroscopic characteristics of multiphase fluid flow, X-ray computed microtomography (micro-CT) emerges as a powerful tool. In contrast to lab-based X-ray micro-CT (XCT), synchrotron X-ray micro-CT (SXCT) images are commonly free of artefacts (i.e. beam hardening) and the unique properties of synchrotron sources enable the X-ray imaging of complex and heterogeneous materials in greater detail, with higher quality, and short acquisition time. This work reports results of cone beam computed microtomography (XCT) in comparison with synchrotron computed microtomography (SXCT) applied to very heterogeneous carbonate and sandstone reservoir rocks. We analyze the quality of the image generated in terms of detection of details and artefacts, the advantages and limitation of each technique, as well as features like contrast, sharpness, and signal-to-noise ratio (SNR). Although SXCT offers significant advantages over XCT, the latter gains in cost of operation, accessibility and user-friendliness.

Innovative solutions have been designed to meet the global demand for energy and environmental sustainability, such as enhanced hydrocarbon recovery and geo-sequestration of CO2. These processes involve the movement of immiscible fluids through permeable rocks, which is affected by the interfacial properties of rocks at the pore scale. Overcoming major challenges in these processes relies on a deeper understanding about the fundamental factors that control the rock wettability. In particular, the efficiency of oil recovery strategies depends largely on the 3D wetting pattern of reservoir rocks, which is in turn affected by the adsorption and deposition of ‘contaminant’ molecules on the pores’ surface. Here, we combined high-resolution neutron tomography (NT) and synchrotron X-ray tomography (XRT) to probe the previously unobserved 3D distribution of molecular and mineralogical heterogeneity of oil reservoir rocks at the pore scale. Retrieving the distribution of neutron attenuation coefficients by Monte Carlo simulations, 3D molecular chemical mappings with micrometer dimensions could be provided. This approach allows us to identify co-localization of mineral phases with chemically distinct hydrogen-containing molecules, providing a solid foundation for the understanding of the interfacial phenomena involved in multiphase fluid flow in permeable media.