Abstract Pseudoboehmite (AlOOH.xH2O) is one of the precursors of alumina. Its calcination produces different phases of alumina and at 1200º C the most stable phase, α-alumina, is formed. The synthesis of pseudoboehmite by the sol-gel process results in a product with high purity, high specific surface area, and high reproducibility. The aging of the pseudoboehmite at temperatures above room temperature results in pseudoboehmites with distinct properties. In this work we report the synthesis of pseudoboehmite by the sol-gel process, using aluminum nitrate and aluminum chloride as precursors, and investigate the effect of acetate ion on crystallinity, adsorption capacity, particle morphology, thermal properties and specific surface area. The X-ray diffraction data of the synthesized pseudoboehmites in the presence of the acetate ion revealed high quality nanoparticles.

Aluminum beverage cans should have very specific crystallographic textures to increase productivity, reduce losses and reduce the amount of material. The present work seeks to add information on the crystallographic texture of aluminum alloy 3104 H-19 during the different manufacturing steps, which undergoes a flat sheet of metal for a cylindrical body. The work scope encompasses from the cup drawing to the final ironing operation and its objective is to add information on the texture evolution of the aluminum alloy undergoes in the intermediary steps. Crystallographic texture continues to change from the drawn cup through the ironing stages. This rotation is assumed to be a grain alignment with the plastic flow of the material.

Resumen En este trabajo se presenta la caracterización de una escoria de aluminio proveniente de la industria primaria, con tamaño de partícula inferior a 3.35 mm. Inicialmente el material fue separado en cuatro fracciones granulométricas las cuales fueron analizadas mediante difracción de rayos X con el fin de analizar la cantidad de cada una de las fases cristalinas presentes en la escoria. Se encontraron las siguientes fases: aluminio metálico, óxido de aluminio, espinelio, espinelio con defecto, diaoyudaoite y nitruro de aluminio. La dependencia del tamaño de partícula con la cantidad de cada una de las fases cristalinas fue analizada mediante un análisis de varianza (ANOVA) con un nivel de confianza del 99%. Del análisis estadístico se pudo concluir que la variación en el contenido encontrado de cada fase cristalina es explicada en un alto porcentaje por el tamaño de partícula.

Abstract The Rietveld method was used in order to determine the amount of crystalline phases present in aluminum dross with particle size less than 3.35 mm. Initially, the dross was separated in four granulometric fractions by screening. Two samples of each granulometric size were obtained by means of quartering and homogenization. Each sample was grounded and subsequently analyzed by X-ray diffraction in order to identify and quantify the crystalline phases present in the dross. Metallic aluminum, aluminum oxide, spinel, defect spinel, diaoyudaoite and aluminum nitride were identified and then quantified by the Rietveld method. In order to observe the dependence of the particle size with the amount of each phase, statistical analyses was done by means of analyses of variance (ANOVA). The coefficient of determination R2 was greater than 94% for all phases except for the NaAl11O17 phase. Thus, the amount of each crystalline phase is satisfactory explained by particle size.

Ternary Ni-W-P films were produced by electroless deposition using baths with different tungsten concentrations. After deposition, the coated surfaces were annealed at 400°C for 1h. Surface morphology and film composition in the as-plated condition were assessed by SEM and EDS analyses, respectively. The crystalline phases after annealing were investigated by X-ray diffraction (XRD). Nanoindentation tests were performed to assess the mechanical properties of the deposited films. Surface roughness was determined by confocal laser scanning microscopy (CLSM). Friction coefficient was evaluated by reciprocating were tests in a nanotribometer. The corrosion behavior was evaluated by potentiodynamic polarization curves. The results showed that the surface morphology, crystallization behavior and corrosion resistance were affected by the tungsten content in the film. The best corrosion performance was obtained for the ternary films after annealing. Hardness, surface roughness and friction coefficient were dependent of the tungsten concentration in the film.

In the current work, XRD, SEM, EBSD and TEM techniques were used to evaluate the microstructure of stainless Fe-Mn-Si-Cr-Ni-Co shape memory steel processed by ECAE and annealed for one hour at temperatures ranging from 650ºC to 950ºC. The results were then correlated with the mechanical and shape-memory properties of the steel. It was observed that the samples containing large grains and a microstructure free of defects or precipitates presented a high volume fraction of multi-variant thermal martensite and stress-induced martensite, resulting in good shape recovery, owing to the memory effect. The grain refinement and precipitation of second-phase particles decreased the volume fraction and number of martensite variants and considerably increased the mechanical resistance, enhancing the elastic shape recovery. It was shown that shape memory properties were essentially related to the mechanical resistance of the matrix, which in turn was related to the microstructure.

The production of tribological nanoscale multilayer CrN/NbN coatings up to 6 µm thick by Sputtering/HIPIMS has been reported in literature. However, high demanding applications, such as internal combustion engine parts, need thicker coatings (>30 µm). The production of such parts by sputtering would be economically restrictive due to low deposition rates. In this work, nanoscale multilayer CrN/NbN coatings were produced in a high-deposition rate, industrial-size, Cathodic Arc Physical Vapor Deposition (ARC-PVD) chamber, containing three cathodes in alternate positions (Cr/Nb/Cr). Four 30 µm thick NbN/CrN multilayer coatings with different periodicities (20, 10, 7.5 and 4 nm) were produced. The coatings were characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The multilayer coating system was composed of alternate cubic rock-salt CrN and NbN layers, coherently strained due to lattice mismatch. The film grew with columnar morphology through the entire stratified structure. The periodicities adopted were maintained throughout the entire coating. The 20 nm periodicity coating showed separate NbN and CrN peaks in the XRD patterns, while for the lower periodicity (≤10nm) coatings, just one intermediate lattice (d-spacing) was detected. An almost linear increase of hardness with decreasing bilayer period indicates that interfacial effects can dominate the hardening mechanisms.

Pitting corrosion of the aluminium cladding of spent nuclear fuels stored in light water pools has been observed. To prevent this, coating of the Al cladding with hydrotalcite (HTC) was proposed. This paper presents the effect of chemical bath and processing parameters on microstructure and corrosion behavior of HTC coatings on alloy AA 6061 specimens. The HTC coating from the high temperature nitrate bath was homogeneous, thicker and consisted of well-defined intersecting platelets than that formed from the room temperature carbonate bath. Electrochemical polarization tests carried out with HTC coated AA 6061 specimens in 0.01 M NaCl revealed that specimens coated with HTC from the nitrate bath and further treated in a cerium salt solution were the most resistant to corrosion. Field tests in which un-coated and coated AA 6061 alloy coupons as well as full-size plates were exposed to the IEA-R1 reactor's spent fuel basin for duration of up to 14 months further corroborated the high corrosion resistance imparted by the high temperature HTC + Ce coating. The mechanism by which the HTC coating and cerium protect the Al alloy is discussed.

O estudo da recristalização de chapas metálicas laminadas a frio é muito útil para a obtenção da temperatura de amolecimento do material submetido a um tratamento térmico. Além disto, a textura cristalográfica pode mudar com a recristalização e com a laminação do metal. Utilizando-se dessas etapas de processamento do material, a orientação dos grãos de uma tira metálica pode ser otimizada, a fim de, por exemplo, melhorar a estampabilidade de chapas, na obtenção de um dado produto com valor agregado. Nesse trabalho, as curvas de amolecimento, para duas chapas produzidas por lingotamento contínuo e lingotamento semicontínuo da liga de alumínio AA4006, foram determinadas e comparadas. Embora as diferenças detectadas entre as curvas de amolecimento tenham sido pequenas, foi possível verificar que a recristalização da chapa produzida por lingotamento contínuo ocorre em temperaturas mais elevadas do que na chapa produzida por lingotamento semicontínuo. Resultados da textura cristalográfica, em amostras dessas chapas, foram obtidos utilizando-se da difração de raios X e da difração de elétrons retroespalhados EBSD. Esses resultados indicaram a presença da textura de cisalhamento na superfície e da fibra β no centro da amostra laminada a frio (70% de redução) da chapa obtida por lingotamento contínuo. Na amostra da chapa obtida por lingotamento semicontínuo, nas mesmas condições, a componente cubo e a fibra β foram detectadas na superfície e no centro. Uma textura fraca com grãos orientados ao acaso foi vista nas duas amostras recristalizadas das duas chapas, devido possivelmente à nucleação estimulada por partículas.

A recrystallization study of cold rolled metallic sheets is very important to evaluate the softening temperature for subsequent annealing. Crystallographic texture evolves during metal rolling and recrystallization. These processing steps can lead to an optimization of the grain orientation distribution in a metal strip and can improve, for instance, the stamping process, hence leading to a product with aggregated value. Softening curves were determined and compared for two sheets of the AA4006 aluminum alloy produced by the twin roll caster-TRC and by the direct chill-DC (under industrial process condition). It has been detected that the recrystallization of the strip produced by TRC process occurs at a higher temperature than the produced by DC process despite the little differences in their softening curves. The precipitation, in the TRC strip sample, occurs mainly before recrystallization and may occur during recrystallization. There is precipitation occurrence before and during recrystallization more expressive in the DC strip sample. Crystallographic texture of the sheet samples was obtained by X-ray diffraction and electron back scattering diffraction (EBSD) techniques. Results indicated the presence of a shear texture at the surface and β-fiber at the center of the cold rolled (70% area reduction) sample for the sheet produced by TRC process. In the strip sample obtained by the DC process, under the same conditions, the cube component and the β-fiber on the surface and at the center were observed. A random oriented grain texture has been detected in the two (TRC and DC) recrystallized (after cold rolling) sheet samples possibly due to the particle stimulated nucleation. The absence of β fiber in the recrystallized samples (TRC and DC) has also been observed.

Nesse trabalho, foi realizado um estudo comparativo da microestrutura e da textura cristalográfica entre chapas da liga AA4006 produzidas por dois processos industriais de lingotamento: contínuo (Twin roll caster TRC) e semicontínuo (Direct chill DC). Para a caracterização microestrutural, foram utilizadas as técnicas de microscopia óptica com luz polarizada, microscopia eletrônica de varredura, medidas de condutividade elétrica e ensaios de dureza Brinell. A textura cristalográfica foi determinada por difração de raios X. Foram detectadas e discutidas diferenças significativas nas morfologias e distribuições de grãos e de partículas de fases intermetálicas. O estudo da textura cristalográfica foi realizado ao longo da espessura das tiras e os resultados mostraram variações significativas da textura entre as chapas ao longo da espessura. A chapa produzida por lingotamento contínuo apresentou uma típica textura de cisalhamento, nas proximidades de sua superfície, enquanto que, nas regiões mais internas, a fibra β foi observada.

A comparative microstructural study has been performed in AA4006 alloy strips produced by two industrial casting processes: twin roll caster (TRC) and direct chill (DC). Polarized optical microscopy, scanning electron microscopy, electrical conductivity measurements and Brinnel hardness tests were used for microstructural characterization. X-ray diffraction was used for texture characterization. Significant differences in the morphologies and distributions of the grains and intermetallic particles were detected and are discussed herein. The crystallographic texture throughout the thickness of these strips was determined and the results presented significant differences. Texture analysis was carried out using the X-ray diffraction technique. The twin roll caster (TRC) sheet presented a typical shear texture near the surface, while internally, the β-fiber was observed.

Nesse trabalho, foram estudados aspectos cinéticos da transformação bainítica incompleta em ligas de ferro nodular, contendo 2,36 e 2,68% Si. As amostras foram austenitizadas a 900°C, durante 90 minutos, e austemperadas a 320 e 370ºC, em tempos entre 1,5 e 60 minutos. A caracterização microestrutural foi realizada pelas técnicas de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de Raios X (DRX) e microdureza Vickers. Foi desenvolvido um método de quantificação das frações transformadas por microscopia óptica. Devido ao elevado teor de silício, as ligas apresentaram o fenômeno de estase da transformação bainítica. As amostras tratadas a 320°C apresentaram microestrutura mais refinada e maiores frações transformadas para o início da estase da reação. As frações transformadas obtidas por DRX foram menores que as encontradas por MO. Esse fenômeno foi mais intenso para a menor temperatura de austêmpera. Curvas de transformação isotérmica foram obtidas para todas as condições estudadas. A cinética de transformação bainítica incompleta foi analisada segundo o modelo de Johnson-Mehl-Avrami-Kolmogorov (JMAK). Os valores do expoente n da equação JMAK variaram entre 0,15 e 0,67.

This work aimed at studying the kinetic aspects of the incomplete bainite transformation of ductile cast iron containing 2.36 and 2.68% silicon (in wt %). Samples were initially austenitized at 900°C during 90 minutes and then austempered at 320 and 370°C in times ranging from 1.5 to 60 minutes. Microstructural characterization was performed by light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers microhardness tests. A LOM-based method for transformed fractions quantification has been developed. Due to its high silicon content, both alloys presented the bainite transformation stasis phenomenon. Samples austempered at 320°C displayed more refined microstructures and higher transformed volume fractions at the reaction stasis beginning. Low resolution is the main drawback for using light optical microscopy in the phase quantification. Transformed volume fractions determined by XRD showed smaller values than those obtained by LOM, mainly for the lower austempering temperature. Kinetic transformation curves have been determined for all studied conditions. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was used to study the incomplete bainite transformation kinetics. Avrami exponents varied from 0.15 to 0.67.

A evolução da textura, nos estados "como recebido", laminado a frio, recozido e após a estampagem, e a estampabilidade de aços inoxidáveis ferríticos AISI 430, estabilizados ao nióbio, foram estudadas. Duas corridas de chapas com espessuras de 3,0 e 0,7 mm foram utilizadas. A de maior espessura foi relaminada a frio e recozida. A de menor espessura, de composição química semelhante à primeira, foi laminada a frio, na usina siderúrgica, e, posteriormente, submetida a estampagem. A textura foi avaliada usando DRX em todas as condições. O aço AISI 430, na condição "como recebido", apresentou forte textura {100}<110>, {100}<120> e a fibra g. Após a deformação, a intensidade da fibra g aumentou e apareceu a fibra a. O recozimento causou o desaparecimento da fibra a e o fortalecimento da fibra g, que é uma textura adequada para a estampagem. Embora o aço AISI 430, de espessura 0,7 mm, tivesse apresentado uma forte textura de fibra g, no estado inicial, as propriedades de estampagem não foram boas e o material trincou durante a conformação.

Texture evolution in AISI 430 Nb stabilized ferritic stainless steels in the "as-received", hot-and cold-rolled, annealed and stamped conditions have been studied, along with their formability. Two ferritic stainless steels (Nb stabilized) having a thickness of 3.0 and 0.7mm, were employed. The thicker one was cold rolled and annealed. The thinner one, with similar composition, was cold rolled at the steel plant and subsequently submitted to deep drawing. Texture has been evaluated using DRX for all conditions. The AISI 430 stainless steel, in the "as-received" condition presented a strong {100} texture in the <110> and <120> directions and the gamma fibre. After cold rolling the material presented stronger gamma and weaker alpha fibres. Annealing of the cold rolled steel conduced to the vanishing of the alpha fibre and strengthening of the gamma fibre, adequate for deep drawing operations. Although the AISI 430 stainless steel of 0.7mm presented a strong gamma fibre, other deep drawing properties were inadequate and the material cracked on stamping.

Cr3C2-Ni20Cr coatings have been used for corrosion and wear resistant applications. However, one of the shortcomings of these coatings is its low hardness, and consequent low wear resistance, for long term high temperature applications. Nanostructured coatings of many materials have exhibited higher hardness and strength compared with conventional coatings of the same material. Consequently, nanostructured coatings of other materials, including Cr3C2-Ni20Cr have been attempted to enhance overall performance. In this study the effects of high energy milling parameters on Cr3C2-25(Ni20Cr) powder characteristics as well as the microstructure and mechanical properties of nanostructured Cr3C2-25(Ni20Cr) coatings formed by high velocity oxygen fuel (HVOF) spraying have been evaluated. The average particle size and crystallite size of milled Cr3C2-25(Ni20Cr) powders decreased with increase in milling time and this decrease was more pronounced in nitrogen compared to that in hexane. This difference has been attributed to a cushioning effect in the latter medium. The coatings prepared with milled Cr3C2-25(Ni20Cr) powders had a more uniform microstructure, were harder and had higher relative fracture toughness compared with coatings prepared with as-received powders.

O Efeito de Memória de Forma em ligas inoxidáveis está associado à transformação martensítica não termoelástica gama (cfc)<FONT FACE=Symbol>«</FONT> épsilon (hc). Trabalhos recentes do grupo têm demonstrado que o tamanho de grão da fase austenítica é um dos parâmetros importantes no grau de recuperação de forma bem como em outras propriedades como a tensão de escoamento, dureza e teor de martensita induzida. Usando a técnica de EBSD, esse trabalho mostra que, além dos parâmetros anteriormente mencionados, o número de orientações das variantes da martensita decresce com o decréscimo do tamanho de grão.

The shape memory effect of stainless shape memory alloy is associated to non-thermolastic gamma (CFC) <FONT FACE=Symbol>«</FONT> epsilon (HCP) martensitic transformation. Recent results generated by our group have demonstrated that the parent austenite grain size is an important parameter for the degree of shape recovery and also in some others properties such as yield stress, hardness and volume fraction of thermal martensite. Using EBSD, this work shows that besides the above-mentioned parameters, the number of martensite orientation variants decreases when the grain size decreases.

Aluminium-silicon alloys have been wide accepted in the automotive, electric and aerospace industries. Preferred orientation is a very common condition for metals and alloys. Particularly, aluminium induces texture during the forming process. The preparation of an aggregate with completely random crystal orientation is a difficult task. The present work was undertaken to analyse the texture by X-ray diffraction techniques, of three spray formed hypereutectic Al-Si alloys. Samples were taken from a billet of an experimental alloy (alloy 1) and were subsequently hot-rolled and cold-rolled (height reduction), 72% and 70%, respectively. The other used samples, alloys 2 and 3, were taken from cylinders liners. The results from the Laue camera showed texture just in the axial direction of alloy 3. The pole figures also indicated the presence of a typical low intensity deformation texture, especially for alloy 3. The spray formed microstructure, which is very fine, hinders the Al-Si texture formation during mechanical work.