ABSTRACT In this study, Equal-Channel Angular Sheet Drawing- ECASD with a die set at 135° was used to produce plastic deformation onto an aluminum alloy AA-1100-O and a magnesium alloy AZ31-O samples, expecting a decreasing the grain size in order to increase the plasticity of these alloys under certain specific working conditions. In this study, the microstructural and mechanical properties changed due to this process were analyzed by optical microscopy and mechanical testing like micro-hardness and tension test. ECASD produces work hardening with no significant dimensional changes into the flat specimens with small changes in the microstructural characteristics. The ECASD process also produces important microstructural changes close to the surface of the investigated samples therefore its hardness is strongly modified in this region. This is due to the high contact stresses and friction developed with the die during the ECASD process.

RESUMEN En este estudio, se usó la técnica de extrusión de láminas de una aleación de aluminio AA-1100-O y una aleación de magnesio AZ31-O por medio de un dado de cizalladura con un ángulo de 135 ° (ECASD, por sus siglas en inglés) para producir la deformación plástica en las aleaciones, que permita obtener microestructuras con tamaños de grano pequeños para aumentar su plasticidad en situaciones específicas de trabajo. En este estudio, se evaluó el cambio en las propiedades microestructurales y mecánicas por medio de microscopía óptica y ensayos mecánicos como microdureza y ensayos de tensión. La técnica de deformación plástica severa ECASD produce cambios en las propiedades mecánicas, sin cambios significativos en la masa de las muestras con pequeños cambios en las características micro-estructurales en el núcleo del material. Sin embargo, el proceso ECASD produce importantes cambios microestructurales cerca de la superficie de los materiales investigados, por tanto, la dureza está fuertemente modificada en esta región. Esto es debido a las altas tensiones de contacto y fricción desarrolladas con la matriz durante el proceso de ECASD.

Los recubrimientos de aluminio depositados sobre el acero inoxidable austenítico AISI 317 por Deposición Química de Vapor en Lecho Fluidizado (CVD-FBR) presentan a altas temperaturas una reducción de la velocidad de corrosión de más de 80 veces. Se realizó la caracterización mecánica de los recubrimientos por medio de microdureza, nanoindentación, para conocer cómo se vieron afectas las propiedades mecánicas (en especial la dureza y el módulo de Young) del recubrimiento y del sustrato luego de ser sometidos a la oxidación a alta temperatura. También se hicieron análisis por medio de Microscopia Electrónica de Barrido (MEB), para observar los cambios microestructurales, y de Microscopia de Fuerza Atómica (MFA), para observar cómo varía la topografía y el gradiente de rugosidad en función de la distancia recorrida por la punta del cantiléver durante los barridos.

The aluminum coatings deposited by Chemical Vapour Deposition Fluidisation (FBR-CVD) on the austenitic stainless steel AISI 317, show a more than 80 times corrosion rate reduction at high temperatures. The coatings mechanical characterization was conducted by means of microhardness, nano indentation, in order to konow how were affected the coating and the substrate’s mechanical properties (particularly the hardness and the Young’s modulus) after being subjected to oxidation at high temperature. Some analyses were also made by means of SEM, to observe the micro structural changes and to see how is the AFM topography and rugosity gradient variation, related to the distance traveled by the tip of the cantilever during the sweeps.

Os recobrimentos de alumínio depositados sobre o aço inoxidável austenítico AISI 317 por Deposição Química de Vapor em Leito Fluidizado (CVD-FBR) apresentam a altas temperaturas uma redução da velocidade de corrosão de mais de 80 vezes. Realizou-se a caracterização mecânica dos recobrimentos por meio de microdureza, nanoindentação, para conhecer como foram afetadas as propriedades mecânicas (em especial a dureza e o módulo de Young) do recobrimento e do substrato após serem submetidos à oxidação a alta temperatura. Também foi feita a análise por meio de Microscopia Eletrônica de Varredura (MEB), para observar as mudanças microestruturais, e de Microscopia de Força Atômica (MFA), para observar como varia a topografia e o gradiente de rugosidade em função da distância recorrida pela ponta do cantiléver durante a varredura.

ABSTRACTIn recent years, due to their high specific mechanical properties, the polymer matrix composites have been widely used. In particular, carbon nanotubes (CNTs) have been used as reinforcement due to its exceptional mechanical and electrical properties. In this work the mechanical behavior of polyvinyl alcohol (PVA) reinforced with different percentages of mechanically oriented CNTs was studied. The composite material was made starting with a solution of PVA+ distilled water, and then the CNTs were added to the solution and dispersed by magnetic stirring and ultrasonic agitation. During this step, a surfactant was added to help with the CNTs dispersion. This mixture was poured into a container and dried using a heat source to accelerate its polymerization and curing. The layers obtained were subjected to mechanical stretching at controlled temperature to align the CNTs in the loading direction. The mechanical properties were measured by tensile testing and nanoindentation. The results show a large increase in modulus and hardness compared with non-reinforced polymeric material, it was also found a significant increase in the tensile strength. The composite with the best properties was subjected to thermal stabilization by ethanol, obtaining an increase in the degradation temperature of about 100°C approximately, although in this case the mechanical stiffness and hardness were decreased compared to unstabilized material, the usefulness of this material is enhanced.

Depth sensing indentation study was conducted in a Fischerscope H100V machine, equipped with a Vickers indenter with a tip roundness of approximately 1330 nm. Tests were carried out on soda-lime glass, fused silica, sapphire, aluminum (1100 alloy), high alloyed steel, titanium and copper. The widely used iterative method of Oliver and Pharr was unsuccessful in the attempts to analyze machine compliance and indenter area function. Therefore, an alternative procedure was adopted. The alternative procedure is based on the ratio between maximum load and unload stiffness squared, Pm/Su². It was found that this procedure, which is not iterative, gives good results. A careful study of the Pm/Su² ratio, lead us to conclude that the Fischercope machine has a low compliance which depends on the sample mounting. This low compliance in conjunction with the recent discovery of the dependence of beta factor on the tip roundness/maximum depth ratio, which appears in the relation between contact stiffness and contact area, explains why the iterative method does not converge. However, variations in beta and machine compliance produces deviation on the hardness and elastic modulus lower that 6% with respect to expected values for the materials and the machine studied in this work.

: Las técnicas de indentación poseen una gran versatilidad que permite evaluar propiedades mecánicas en volúmenes inferiores a 0.001 µm3, hasta volúmenes del orden de los mm3, útil tanto en materiales compuestos como en volumen. Este artículo hace una revisión general de los fundamentos de éstas técnicas. También se muestran algunas de las dificultades que surgen cuando éstas son aplicadas a la medición de propiedades mecánicas de materiales cerámicos, tales como su dureza tenacidad a la fractura, módulo de elasticidad y adherencia de capas cerámicas en sustratos metálicos. Para esto se utilizan algunos materiales cerámicos en volumen como alúmina Al2O3, Titanato de Bario BaTiO3 y capas TiN depositadas sobre acero M2.

Indentation techniques offer a width spread possibilities to measure mechanical properties in small volumes ranged from 0.001 µm3, to volumes of several mm3, useful in both bulk and in composite materials. This paper discus some of the fundamentals of the indentation theory and shows some important draw falls when indentation techniques are utilized to evaluate mechanical properties of ceramic materials. Among the properties are hardness, fracture toughness, elastic modulus and film adherence to substrate. To achieve it, bulk ceramic materials as Al2O3, Barium Titanate BaTiO3 and TiN films deposited onto M2 tool steel were used as a case study.