Navegando por Palavras-chave "Severe Plastic Deformation"

Agora exibindo 1 - 2 de 2
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Influência do processamento por deformação plástica severa na oxidação do magnésio
    (Universidade Federal de São Paulo (UNIFESP), 2020-08-31) Melo, Samantha Sousa De [UNIFESP]; Andreani, Gisele Ferreira De Lima [UNIFESP]; Universidade Federal de São Paulo
    Magnesium is one of the lightest structural metals and its alloys have important applications in the automotive and aerospace industry, where the use of lightweight materials results in low fuel consumption (reducing pollutant emissions and global warming), and they have the potential for hydrogen storage application (in form of hydrides). The disadvantages of magnesium are the low melting point (650 ° C) and the high rate of corrosion and of oxidation, which degrade its mechanical and hydrogenation properties. The severe plastic deformation (SPD) processes, such as angular channel extrusion (ECAP) and cold rolling (CR), can produce ultrafine grains or nanostructures, but in bulk forms, where lower surface/volume ratio and specific textures contribute for air (oxidation) resistance. The objective of this work was to submit the commercial pure magnesium to processing routes of ECAP and ECAP+CR, and to study the relationship between the structures and oxidation resistances. The processed samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the oxidation resistance was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The ECAP process promoted grain refinement in all tested conditions (varing: temperature 25 and 300°C; dies; numbers of passes 1, 4 and 8; and thicknesses). Between all conditions of ECAP and route (ECAP or ECAP+CR), the best result was obtained for the sample submitted to ECAP at 300°C and 4 passes (with grain size of ~32 nm and higher orientation along (101) plan) that presented the highest ignition temperature (778°C), being this 188°C higher than the values reported in the literature for powders, and 120°C higher than as received ingot. The results suggest that the microstructure and the preferred orientation along (101) plan are related with ignition temperatures and with MgO stabilization, which reflects in the oxidation rate. After the ECAP, samples with different thicknesses exhibited oxidation results that were in close proximity to each other.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Processamento do compósito de matriz de liga de alumínio AA6061 reforçada por nanotubos de carbono de paredes múltiplas por Equal Channel Angular Pressing (ECAP)
    (Universidade Federal de São Paulo (UNIFESP), 2019-06-21) Jimenez, Laila Ribeiro De Andrade Acevedo [UNIFESP]; Travessa, Dilermando Nagle [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    There has been increase in the need for materials that combine high mechanical resistance and low weight, foremost in aeronautical industry. Aluminum AA6061 alloys based metal matrix composites (MMC) reinforced by Multiple Walled Carbon Nanotube (MWCNT) are very interesting because they combine these properties. To optimize the distribution of the reinforcement along the matrix is indispensable to achieve the desirable properties in a composite. However, the MWCNT is formed of nanometric particles that tend to form clusters, and dissolve them to obtain a well-distributed reinforcement in the matrix can be a challenging step on the processing of the composite. ECAP (Equal Channel Angular Pressing) can be an efficient technique for producing microstructural refinement by promoting reinforcement distribution on the metal matrix when applied to composites. In this project, extruded bars of AA6061 composite reinforced with 2% MWCNT produced by powder metallurgy were successfully processed by 4 ECAP passes, using rout Bc and temperature of 200°C. ECAP produced microstructural modifications that reflected in hardness increase of 6,5%, mantainig ductility, when compared to its starting condition, as extruded (AE) bars, and yield stress of the processed composite values that were up to 388 MPa, under compression test.