ABSTRACT During production and heat treatments of aluminum alloys, numerous second phase particles form, which maximizes their mechanical properties. This work aimed to perform a correlation between Vickers hardness and X-ray diffraction results, when 7475-T7351 aluminum alloy processed by the cross rolling is subjected to annealing heat treatments (AHT) at 500 °C for different soaking times (15, 30 and 60 minutes) and for a soaking time of 15 minutes at different temperatures (200, 300 and 400 °C). The influence of the AHT (500 °C / 15 minutes) on the microstructure, via scanning and transmission electron microscopy, and tensile tests properties was also investigated. The results show evidence that the Vickers hardness decreased for AHT performed at 200 and 300 °C / 15 minutes and increase for greater temperatures and times. This behavior is probably due to modifications in the constituent/dispersoid particles and aluminum matrix observed from the X-ray analysis. Partial recrystallization and a coarsening of the precipitates was observed after the AHT at 500 °C / 60 minutes, whose brought harmful effects on the tensile mechanical properties.

ABSTRACT The pure copper wires were wiredrawn at cryogenic and room temperatures. After deformation they presented important and significant differences in their crystallographic textures and microstructures. Therefore, this study aimed to investigate the evolution of crystallographic texture of pure copper drawn at temperatures of 295 K and 77 K and correlated them to the deformation micromechanisms. For this, the X ray diffraction (XRD) and electron backscattered diffraction (EBSD) techniques were used. The results showed that, after the deformation, the samples drawn at both temperatures showed Copper {112}<111>, X {110}<111> and Brass {110}<112> components as the most intense. In samples drawn at cryogenic temperature there was also observed the appearance of a R{124}<211> component, typical of recrystallization and the presence of the γ fiber {111}<uvw>, typical of deformation twin.

The 304L austenitic stainless steel is susceptible to mechanically induced martensitic transformation from slightly above room temperature down to cryogenic temperatures. In this work, austenitic 304L steel produced by two different thermomechanical processes, hot rolling (HR) and cold rolling and annealing (CR/A), were subjected to martensitic transformation by rolling and by tensile tests at 298 K and 155 K and the volume fraction of martensite was determined by X-ray diffraction and ferritescope measurements. The results showed that the martensitic transformation was complete for CR/A samples rolled at 155 K and that the volume fraction of martensite was larger in CR/A samples than in HR samples in all cases.

ABSTRACT Samples of the Al 7075 naturally and artificially aged were processed by conventional and asymmetrical rolling with 5% of thickness reduction. The rolling processes were evaluated under room temperature and under warm condition (130°C). Mechanical properties were evaluated by uniaxial tensile and Vickers microhardness tests. Microstructure evolutions were followed by optical microscopy analysis. Naturally aged samples showed better yield strengthening under warm processing. Greater ultimate stress and ductility under room temperature processing was also noticed in naturally aged specimens. Artificially aged samples showed better mechanical properties under room temperature, softening under warm processing due to grain recovery process. Microhardness tests showed expected results for both rolling types, especially on asymmetrical rolling with the higher predictions were observed. Micrographs have shown no expressive grain changes or refinement although its flattening was observed. Precipitates were analyzed by EDS/SEM revealing the presence of MgZn2 and CuMgAl along the matrix that provides plastic strengthening.

Analysis of dislocation density in metallic materials has been pursued with great interest for many years because dislocations are closely associated with plastic deformation and thus exert a deep effect on the mechanical properties of any material. Crystallographic texture has also a decisive influence in some properties. In this work, the dislocation density was estimated from the line broadening of X-ray diffractograms using the Convolutional Multiple Whole Profile Program (CMWP) and crystallographic texture analyses were performed using inverse pole figures (IPF). The material used in this research was pure copper deformed by cold rolling and Equal Channel Angular Pressing (ECAP). The dislocation density values obtained by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) were compared and discussed. While, in the case of cold rolling, the crystallographic texture of the material was enhanced with increasing deformation, it was reduced with increasing deformation in the case of ECAP processing.

Stainless steels are well known by their corrosion resistance. The austenitic types, in particular, are also applied as structural components in engineering systems operating at high temperatures such as nuclear reactors, petrochemical furnaces and turbines. For these applications operational temperatures may go up to 800ºC. Under constant load applications the main mechanism of failure, which would limit the material's life, is creep. In the present work creep parameters were evaluated in the high temperature interval of 600 to 800ºC for an AISI 316 austenitic stainless steel. Dislocation substructures were observed by transmission electron microscopy in creep ruptured specimens. Two distinct mechanisms of dynamic strain aging and dynamic recovery associated with different values for the power law exponent n and the Arrhenius activation energy Q for creep were verified below and above 700ºC, respectively.

Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.

RESUMO Neste trabalho foram preparadas dispersões aquosas de óxido de grafeno (GO) e óxido de grafeno reduzido (rGO), em diferentes tempos de oxidação, com o objetivo de verificar a influência do tempo de oxidação em relação às características das folhas (flakes) finais. As dispersões de GO foram preparadas pelo método de Hummers modificado utilizando os seguintes tempos de oxidação: 4 h; 1 dia; 3 dias; 7 dias e 10 dias. Em seguida, as dispersões de GO foram submetidas ao tratamento de redução com ácido ascórbico, obtendo-se o rGO. As caracterizações das amostras foram realizadas por meio das análises de espectroscopia Raman, espectroscopia de fotoelétrons excitados por raios X (XPS), microscopia eletrônica de varredura (MEV) e difração de raios X (DRX). A espectroscopia Raman mostrou a variação da relação de intensidade entre as bandas D e G (ID/IG) à medida que o tempo de oxidação foi aumentado. A análise de XPS exibiu a alteração dos percentuais de carbono (C) e oxigênio (O). Através de análise no MEV foi correlacionada a morfologia dos flakes com o aumento do tempo de oxidação. E por fim, com o auxílio de DRX, foi verificada a variação da distância interplanar.

ABSTRACT In this work aqueous dispersions of graphene oxide (GO) and reduced graphene oxide (rGO) were prepared in different oxidation times in order to verify the influence of the oxidation time on the characteristics of the final flakes. GO dispersions were prepared by the modified Hummers method, using the following oxidation times: 4 h; 1 day; 3 days; 7 days and 10 days. Afterwards the dispersions of GO were subjected to the reduction treatment with ascorbic acid, obtaining the rGO. Samples were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Raman spectroscopy showed the variation of the intensity ratio between the D and G bands (ID / IG) as the oxidation time was increased. The XPS analysis indicated the alteration of the percentages of carbon (C) and oxygen (O). The SEM analysis correlated the morphology of the flakes with the increase of the oxidation time. Finally, with the aid of XRD, the variation of the interplanar distance was verified.