Caracteriza����o das ligas zinco-n��quel eletrodepositadas a partir de solu����o de cloreto

Este trabalho apresenta um estudo da liga zinco-n��quel obtida a partir de um banho ��cido de cloretos, de formula����o sugerida pela Boeing. A liga zinco n��quel �� uma proposta atual para a substitui����o de revestimentos de c��dmio eletrodepositados, tanto na industria aeron��utica como na ind��stria automobil��stica. O interesse nesta substitui����o surge da necessidade de se encontrar um processo menos poluente ao meio ambiente e ao operador que aplica o revestimento, economicamente vi��vel e que tamb��m atenda legisla����o ambiental, cada vez mais restritiva. As ligas zinco-n��quel s��o de especial interesse, porque al��m de apresentarem as caracter��sticas descritas anteriormente, tamb��m conferem ao substrato ferroso, uma prote����o do tipo cat��dico. O estudo aqui apresentado avaliou uma faixa de densidade de corrente de deposi����o, entre 0,5 e 5 A.dm-2 quanto aos teores de n��quel das ligas formadas, a resist��ncia a corros��o e outras caracter��sticas das ligas, atrav��s de curvas de polariza����o, voltametrias e ensaios de imped��ncia eletroqu��mica e ensaios de n��voa salina e outros ensaios . Especial aten����o foi dada para a faixa de densidade de corrente considerada como ��tima pela Boeing, entre 2 e 3 A.dm-2.

Um modelo informacional para gest��o de opera����es : o caso da Cia. Vale do Rio Doce - Depto. de Mangan��s e Ferro-Ligas

Esta pesqUisa objetiva desenvolver, testar e demonstrar a aplicabilidade de um modelo infonnacional que possibilite a gest��o integrada das opera����es da cadeia de suprimentos para ind��strias geograficamente dispersas, tamb��m denominadas ind��strias multi planta. Para tanto, ser��o aplicadas metodologias de estudo de caso e pesquisa-a����o, em uma empresa representativa dos setores mineral e metal��rgico, o Departamento de Mangan��s e Ferro-Ligas da CVRD - Cia. Vale do Rio Doce. A pesquisa pretende demonstrar que o modelo de sistema infonnacional proposto, por meio da automatiza����o dos processos transacionais e gerenciais, �� capaz de prover recursos de planejamento e controle nos n��veis operacional, t��tico e estrat��gico, devido a sua capacidade de incrementar a velocidade e a qualidade dos processos de an��lise e decis��o. A pesquisa pretende conduzir, ap��s an��lise dos resultados e avalia����o das contribui����es �� empresa estudada, a um modelo informacional adequado para gerir as opera����es de outras empresas de minera����o e metalurgia com caracter��sticas semelhantes.

An��lise num��rica e experimental da solidifica����o das ligas Al 3,5% Cu e AA36

A forma����o interna da estrutura de uma pe��a fundida deve determinar as caracter��sticas mec��nicas dessa pe��a, quando em servi��o. Dessa forma, torna-se fundamental conhecer e parametrizar os elementos que influem na forma����o da estrutura do componente s��lido, para o desenvolvimento adequado de sistemas de solidifica����o que permitam conduzir a melhoria da qualidade de uma pe��a no processo de solidifica����o. Modelos num��ricos podem ser empregados para a determina����o da forma����o estrutural, entretanto estes devem ser aferidos adequadamente para garantir sua aplicabilidade. No trabalho em quest��o, desenvolveu-se uma metodologia que permitiu a aferi����o de um modelo num��rico para a previs��o das condi����es de resfriamento de ligas de alum��nio. Elaborou-se um conjunto de coquilhas e moldes que permitiram o acoplamento e verifica����o da estrutura formada na solidifica����o em diferentes situa����es de resfriamento, observando principalmente a dire����o de extra����o de calor e a taxa de resfriamento associada. O modelo num��rico aplicado respondeu coerentemente aos resultados obtidos permitindo a previs��o da estrutura solidificada pela observa����o dos resultados de evolu����o das isotermas solidus e liquidus no interior dos sistemas.

Produ����o de implantes de titânio, via moldagem por inje����o de p��s de hidretos de titânio

O objetivo deste trabalho foi a produ����o e caracteriza����o de componentes sinterizados de titânio para aplica����o biom��dica, obtidos atrav��s do processo de fabrica����o chamado de Moldagem de P��s por Inje����o ( MPI ), ou ���Metal Injection Molding��� ( MIM ) na l��ngua inglesa. Para a produ����o dos componentes de titânio, utilizou-se de p��s de hidreto de titânio produzidos pelo processo de Hidreta����o-Dehidreta����o ( HDH ), no Laborat��rio de Transforma����o Mec��nica - UFRGS. Foram realizados ensaios para a caracteriza����o dos componentes sinterizados quanto ��s suas propriedades mec��nicas, resist��ncia �� corros��o, caracter��sticas morfol��gicas e de biocompatibilidade. Este trabalho concentra-se no desenvolvimento e produ����o de componentes para ��rea odontol��gica ( implantodontia ) e m��dica, visando a implementar a t��cnica de Moldagem de P��s por Inje����o ( MPI ) de hidreto de titânio para aplica����o na produ����o de implantes, tendo em vista que, atualmente, este processo n��o �� utilizado para tal fim. Para as an��lises de biocompatibilidade foram produzidos parafusos corticais para utiliza����o como implantes. Ap��s a caracteriza����o morfol��gica e qu��mica dos implantes produzidos foram realizados ensaios in vitro de corros��o e in vivo de biocompatibilidade onde foi poss��vel observar algumas caracter��sticas da superf��cie do implante como, por exemplo, a susceptibilidade �� corros��o por frestas e elevado recobrimento ��sseo do implante.

Estudo das caracter��sticas f��sico-qu��micas e biol��gicas pela ades��o de osteoblastos em superf��cies de titânio modificadas pela nitreta����o em plasma

SILVA, J. S. P. Estudo das caracter��sticas f��sico-qu��micas e biol��gicas pela ades��o de osteoblastos em superf��cies de titânio modificadas pela nitreta����o em plasma. 2008. 119 f. Tese (Doutorado) - Faculdade de Medicina, Universidade de S��o Paulo. S��o Paulo, 2008.

Avalia����o do estresse oxidativo induzido por superf��cies de titânio

Commercially pure Titanium (cp Ti) is a material largely used in orthopedic and dental implants due to its biocompatibility properties. Changes in the surface of cp Ti can determine the functional response of the cells such as facilitating implant fixation and stabilization, and increased roughness of the surface has been shown to improve adhesion and cellular proliferation. Various surface modification methods have been developed to increase roughness, such as mechanical, chemical, electrochemical and plasma treatment. An argon plasma treatment generates a surface that has good mechanical proprieties without chemical composition modification. Besides the topography, biological responses to the implant contribute significantly to its success. Oxidative stress induced by the biomaterials is considered one of the major causes of implant failure. For this reason the oxidative potential of titanium surfaces subjected to plasma treatment was evaluated on this work. CHO-k1 cells were cultivated on smooth or roughed Ti disks, and after three days, the redox balance was investigated measuring reactive oxygen species (ROS) generation, total antioxidant capacity and biomarkers of ROS attack. The results showed cells grown on titanium surfaces are subjected to intracellular oxidative stress due to hydrogen peroxide generation. Titanium discs subjected to the plasma treatment induced less oxidative stress than the untreated ones, which resulted in improved cellular ability. Our data suggest that plasma treated titanium may be a more biocompatible biomaterial.

Efeito do tratamento t��rmico do titânio sobre a prolifera����o de c��lulas pr��-osteobl��sticas

Titanium is a biomaterial widely employed in biomedical applications (implants, prostheses, valves, stents). Several heat treatments are usually used in order to obtain physical properties required to different applications. This work studied the influence of the heat treatment on microstructure of commercial pure titanium, and their consequences in growth and proliferation of MC3T3-E1 cells. Discs of titanium were treated in different temperatures, and characterized by optical microscopy, image analysis, wettabillity, roughness, hardness and X-ray diffraction. After the heat treatment, significant modifications in these properties were observed. Pattern images of titanium, before and after the cell culture, were compared by overlapping to analyze the influence of microstructure in microstructure and preferences guidance cells. However, in general, titanium discs that showed a higher residual strength also presented an increase of cells numbers on surface

Processamento e an��lise de imagens na caracteriza����o da superf��cie do titânio submetido a um ensaio de cultura de c��lulas

This work aims to develop a methodology for analysis of images using overlapping, which assists in identification of microstructural features in areas of titanium, which may be associated with its biological response. That way, surfaces of titanium heat treated for 08 (eight) different ways have been subjected to a test culture of cells. It was a relationship between the grain, texture and shape of grains of surface of titanium (attacked) trying to relate to the process of proliferation and adhesion. We used an open source software for cell counting adhered to the surface of titanium. The juxtaposition of images before and after cell culture was obtained with the aid of micro-hardness of impressions made on the surface of samples. From this image where there is overlap, it is possible to study a possible relationship between cell growth with microstructural characteristics of the surface of titanium. This methodology was efficient to describe a set of procedures that are useful in the analysis of surfaces of titanium subjected to a culture of cells

Tratamento termoqu��mico do titânio auxiliado por plasma de ar - N2 - O2

Discs were grade II cp Ti oxynitride by plasma of Ar - N2 - O2 using different proportions of individual gases. These ratios were established from analysis of optical emission spectroscopy (OES) of plasma species. The proportions that resulted in species whose spectra showed an abrupt change of light intensity were chosen for this study. Nanohardness tests revealed that there was a correlation between the intensity of N2 + species with the hardness, because the treatments where they had a higher intensity, obtained a higher value nanohardness, although the crystalline phases have remained unchanged. With respect to topography, it was observed that in general, the surface roughness is related to the intensities of plasma species, because they may have different values depending on the behavior of the species. Images obtained by optical microscopy revealed a surface with grains of different colors to optical reflectance showed a peak of reflection in the red area. Measures the contact angle and surface tension showed hydrophilic properties and hydrophilic with little variation of polar and dispersive components of surface tension

Desenvolvimento de um sistema de nitreta����o por plasma em fonte pulsada e sua influencia sobre a nitreta����o do titânio

The pulsed plasma nitriding is a solution currently used in the metallurgical industry to resolve problems earlier in the processing of parts by using plasma DC voltage. These problems consisted mainly of edge effect and opening arches caused due to non-uniformity of electric fields on uneven surfaces. By varying the pulse width can reduce these effects. However, variations in pulse width can drastically affect the population of the plasma species and hence the final microstructure of the nitrided layer. In literature, little is known about the effect of process parameters on the properties of the plasma species and, consequently, the surface properties. We have developed a system of nitriding with pulsed source with fixed period of 800  pulse width is variable. Examined the variation of these parameters on the properties of nitrided surface when keeping constant temperature, gas composition, flow, pressure and power. It was found that the values of width and pulse repetition time of considerable influence in the intensities of the species present in plasma. Moreover, we observed the existence of the edge effect for some values of pulse widths, as well as changes in surface roughness and hardness

Constru����o, caracteriza����o e aplica����o de eletrodos para descarga por arco de c��todo oco

The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and sil��cio, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, sil��cio and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 ��m, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 ��m/min

Influ��ncia dos par��metros de processo na deposi����o de nitreto de titânio por plasma em gaiola cat��dica

Titanium nitride films were grown on glass using the Cathodic Cage Plasma Deposition technique in order to verify the influence of process parameters in optical and structural properties of the films. The plasma atmosphere used was a mixture of Ar, N2 and H2, setting the Ar and N2 gas flows at 4 and 3 sccm, respectively and H2 gas flow varied from 0, 1 to 2 sccm. The deposition process was monitored by Optical Emission Spectroscopy (OES) to investigate the influence of the active species in plasma. It was observed that increasing the H2 gas flow into the plasma the luminescent intensities associated to the species changed. In this case, the luminescence of N2 (391,4nm) species was not proportional to the increasing of the H2 gas into the reactor. Other parameters investigated were diameter and number of holes in the cage. The analysis by Grazing Incidence X-Ray Diffraction (GIXRD) confirmed that the obtained films are composed by TiN and they may have variations in the nitrogen amount into the crystal and in the crystallite size. The optical microscopy images provided information about the homogeneity of the films. The atomic force microscopy (AFM) results revealed some microstructural characteristics and surface roughness. The thickness was measured by ellipsometry. The optical properties such as transmittance and reflectance (they were measured by spectrophotometry) are very sensitive to changes in the crystal lattice of the material, chemical composition and film thicknesses. Therefore, such properties are appropriate tools for verification of this process control. In general, films obtained at 0 sccm of H2 gas flow present a higher transmittance. It can be attributed to the smaller crystalline size due to a higher amount of nitrogen in the TiN lattice. The films obtained at 1 and 2 sccm of H2 gas flow have a golden appearance and XRD pattern showed peaks characteristics of TiN with higher intensity and smaller FWHM (Full Width at Half Maximum) parameter. It suggests that the hydrogen presence in the plasma makes the films more stoichiometric and becomes it more crystalline. It was observed that with higher number of holes in the lid of the cage, close to the region between the lid and the sample and the smaller diameter of the hole, the deposited film is thicker, which is justified by the most probability of plasma species reach effectively the sample and it promotes the growth of the film

An��lise mec��nica e microestrutural das ligas de cobalto-cromo de uso odontol��gico ap��s sucessivas refundi����es

The cobalt-chromium alloy is extensively used in the Odontology for the confection of metallic scaffolding in partial removable denture. During the last few years, it has been reported an increasing number of premature imperfections, with a few months of prosthesis use. The manufacture of these components is made in prosthetic laboratories and normally involves recasting, using parts of casting alloy and parts of virgin alloy. Therefore, the objective of the present study was to analyze the mechanical properties of a commercial cobalt-chromium alloy of odontological use after successive recasting, searching information to guide the dental prosthesis laboratories in the correct manipulation of the cobalt-chromium alloy in the process of casting and the possible limits of recasting in the mechanical properties of this material. Seven sample groups were confectioned, each one containing five test bodies, divided in the following way: G1: casting only with virgin alloy; G2: casting with 50% of the alloy of the G1 + 50% of virgin alloy; G3: casting with 50% of the alloy of the G2 + 50% of virgin alloy; G4: casting with 50% of the alloy of the G3 + 50% of virgin alloy; G5: 50% of alloy of the G4 + 50% of virgin alloy; G6: 50% of alloy of the G5 + 50% of virgin alloy and finally the G7, only with recasting alloy. The modifications in the mechanical behavior of the alloy were evaluated. Moreover, it was carried the micro structural characterization of the material by optic and electronic scanning microscopy, and X ray diffraction.and fluorescence looking into the correlatation of the mechanical alterations with structural modifications of the material caused by successive recasting process. Generally the results showed alterations in the fracture energy of the alloy after successive recasting, resulting mainly of the increasing presence of pores and large voids, characteristic of the casting material. Thus, the interpretation of the results showed that the material did not reveal significant differences with respect to the tensile strength or elastic limit, as a function of successive recasting. The elastic modulus increased from the third recasting cycle on, indicating that the material can be recast only twice. The fracture energy of the material decreased, as the number of recasting cycles increased. With respect to the microhardness, the statistical analyses showedno significant differences. Electronic scanning microscopy revealed the presence of imperfections and defects, resulting of the recasting process. X ray diffraction and fluorescence did not show alterations in the composition of the alloy or the formation of crystalline phases between the analyzed groups. The optical micrographs showed an increasing number of voids and porosity as the material was recast. Therefore, the general conclusion of this study is that the successive recasting of of Co-Cr alloys affects the mechanical properties of the material, consequently leading to the failure of the prosthetic work. Based on the results, the best recommendadition is that the use of the material should be limited to two recasting cycles

Propriedades tribomec��nicas de superf��cies de titânio carbonitretadas por plasma

Interstitial compounds of titanium have been mainly studied due to the large range of properties acquired when C, N, O and H atoms are added. In this work, surfaces of TiCxNy were produced by thermochemical treatments assisted by plasma with different proportions of Ar + N2 + CH4 gas mixture. The Ar gas flow was fixed in 4 sccm, varying only N2 and CH4 gas flows. During the thermochemical treatment, the plasma was monitored by Optical Emission Spectroscopy (OES) for the investigation of the influence of active species. After treatments, C and N concentration profile, crystalline and amorphous phases were analyzed by Nuclear Reaction (NRA). Besides tribomechanical properties of the Ti surface were studied through the nanohardness measurements and friction coefficient determination. The worn areas were evaluated by profilometry and Scanning Electronic Microscope (SEM) in order to verify the wear mechanism present in each material. It has been seen which the properties like nanohardness and friction coefficient have strong relation with luminous intensity of species of the plasma, suggesting a using of this characteristic as a parameter of process

Estudo da sinterabilidade de ligas de n��quel obtidas por meio dos portadores de liga sic, si3n4 ou si met��lico com grafita

Nickel alloys are frequently used in applications that require resistance at high temperatures associated with resistance to corrosion. Alloys of Ni-Si-C can be obtained by means of powder metallurgy in which powder mixtures are made of metallic nickel powders with additions of various alloying carriers for such were used in this study SiC, Si3N4 or Si metal with graphite. Carbonyl Ni powder with mean particle size of 11 mM were mixed with 3 wt% of SiC powders with an average particle size of 15, 30 and 50 μm and further samples were obtained containing 4 to 5% by mass of SiC with average particle size of 15 μm. Samples were also obtained by varying the carrier alloy, these being Si3N4 powder with graphite, with average particle size of 1.5 and 5 μm, respectively. As a metallic Si graphite with average particle size of 12.5 and 5 μm, respectively. The reference material used was nickel carbonyl sintered without adding carriers. Microstructural characterization of the alloys was made by optical microscopy and scanning electron microscopy with semi-quantitative chemical analysis. We determined the densities of the samples and measurement of microhardness. We studied the dissociation of carriers alloy after sintering at 1200 �� C for 60 minutes. Was evaluated also in the same sintering conditions, the influence of the variation of average particle size of the SiC carrier to the proportion of 3% by mass. Finally, we studied the influence of variation of the temperatures of sintering at 950, 1080 and 1200 �� C without landing and also with heights of 30, 60, 120 and 240 minutes for sintering where the temperature was 950 ��C. Dilatometry curves showed that the SiC sintered Ni favors more effectively than other carriers alloy analyzed. SiC with average particle size of 15 μm active sintering the alloy more effectively than other SiC used. However, with the chemical and morphological analyzes for all leagues, it was observed that there was dissociation of SiC and Si3N4, as well as diffusion of Si in Ni matrix and carbon cluster and dispersed in the matrix, which also occurred for the alloys with Si carriers and metallic graphite. So the league that was presented better results containing Si Ni with graphite metallic alloy as carriers, since this had dispersed graphite best in the league, reaching the microstructural model proposed, which is necessary for material characteristic of solid lubricant, so how we got the best results when the density and hardness of the alloy