Aloisio Nelmo Klein - Profile on Academia.edu (original) (raw)
Papers by Aloisio Nelmo Klein
Journal of Materials Processing Technology, 2006
The objective of the paper is to present a general algorithm that enables, in a simple way, the i... more The objective of the paper is to present a general algorithm that enables, in a simple way, the incorporation of a set of well known elasto-plastic constitutive models, for porous sintered materials, and to perform a comparative analysis of these various models. These models were modified in order to incorporate an isotropic work hardening and a porosity coupling behavior and implemented in the ABAQUS @ finite element program. The proposed algorithm considered an operator split technique which decomposed the problem into an elastic predictor followed, if necessary, by a plastic corrector step. The algorithm is presented in a general frame work and is thereafter particularized for a given set of constitutive models for porous sintered materials. In the work is also implemented some of these published elasto-plastic models that have not been implemented previously into FEM programs. Finally, some simple examples are solved with the aim of comparing the performance of these different models.
International Journal of Machine Tools and Manufacture, 2004
The subject of this paper is to analyze the impact of projectiles against ceramic/metal armour us... more The subject of this paper is to analyze the impact of projectiles against ceramic/metal armour using a simple one-dimensional mode. The model allows the calculation of the loss of projectile mass and its velocity, and gives the deflection of the backup material. This work also investigates the influence of grain size of the ceramic material on ballistic performance, which is very useful during selection of the best material for each application. Therefore, two formulations of the same ceramic material were produced. They had the same chemical composition, the same mechanical properties, but different grain size. The ballistic performances were compared measuring the maximum velocity each formulation was able to support, without perforation.
Materia-rio De Janeiro, Sep 1, 2014
the extraction process, resulting in the need to optimize the extraction cycle and thermal sinter... more the extraction process, resulting in the need to optimize the extraction cycle and thermal sintering. Slower cycles and low temperature promoted the complete extraction of the ligands. The Ni-Fe-Cr-P alloy injected showed shrinkage of approximately 50%, and high levels of pores as compared to the compacted material, which influenced the mechanical properties and apparent hardness of the material.
Bulletin of the American Physical Society, Mar 1, 2012
In order to obtain components with improved properties, several alternative techniques, based on ... more In order to obtain components with improved properties, several alternative techniques, based on plasma technology, have been studied. Surface porosity of plain iron could be modified by using plasma sintering. In this work, components produced by PM were sintered on a plasma reactor in the presence of an abnormal glow discharge. Two samples were produced using particles with different range size. One set of samples were produced with the full range of size of the powder (20-200 μm) with mean diameter of 100 μm. Another set of samples were produced using fractioned powder, with particle size fewer than 45 μm. Studies were carried out in order to evaluate the influence of ion energy bombardment and the particle sizes, on the surface porosity and tribological behaviour.
International Journal of Knowledge Engineering and Management, 2020
ANÁLISE DO FLUXO DE CONHECIMENTO NO NÍVEL DOS INDIVÍDUOS EM COLABORAÇÕES UNIVERSIDADE-INDÚSTRIA R... more ANÁLISE DO FLUXO DE CONHECIMENTO NO NÍVEL DOS INDIVÍDUOS EM COLABORAÇÕES UNIVERSIDADE-INDÚSTRIA Resumo Objetivo: Caracterizar o fluxo de conhecimento em colaborações universidadeindústria, no nível dos indivíduos, identificando os fatores que facilitam e dificultam o fluxo. DesignMetodologiaAbordagem: O estudo investiga o fenômeno a partir de uma perspectiva qualitativa, por meio de entrevistas semi-estruturadas e análise temática. Resultados: Apresentou-se uma representação para descrever o fluxo do conhecimento em colaborações universidade-indústria, no nível dos pesquisadores, como um processo iterativo em níveis e etapas. Identificou-se que um dos componentes chave para o fluxo são as interações entre pesquisadores de diferentes níveis e que disponibilidade, distância, contexto e a atuação de intermediadores influenciam a realização destas interações. OriginalidadeValor: Poucos estudos analisam o fluxo de conhecimento no nível dos indivíduos (micro nível). O trabalho evidenciou a importância da análise de fluxo de conhecimento no micro nível, mostrando aos gestores de colaboração universidadeindústria que é fundamental garantir a participação dos diferentes pesquisadores nos vários níveis de interação.
Brazilian Journal of Physics, 2020
We investigated flowing N 2 DC discharges both experimentally and theoretically. The discharge ga... more We investigated flowing N 2 DC discharges both experimentally and theoretically. The discharge gas and N 2 (X 1 Σ + g ) vibrational temperatures, electron density (n e ), reduced electric field (E/N), and radiative state densities were measured by optical emission spectrometry (OES) and Langmuir double probes. We formulated a discharge kinetic numerical model to calculate the densities of nitrogen species as functions of the gas residence time. We combine the experimental parameters measured in the discharge with the kinetic model to analyze different discharge conditions where E/N varies significantly. First, we analyzed the measured and calculated radiative states densities and N 2 (X 1 Σ + g ) vibrational distributions at the end of the positive column. Results show good agreement between calculated and measured parameters. Then, we studied the excited molecular species densities, and neutral and excited atoms densities as functions of the discharge gas residence time. This work presents for the first time the temporal densities of excited molecular and atomic states from 10 -9 to 10 -1 s discharge residence times, calculated for experimental conditions where n e presents a low variation and E/N varies from high (94 Td) to relatively low values (48 Td). The discharge experimental conditions are discharge current of 60 mA, gas pressure of 230-530 Pa, and gas flow rate of 0.9 Slm -1 . Neutral and excited atoms density . Neutral and excited molecule density . Nitrogen flowing discharges * Jacques Levaton
Plasma Research Express, 2019
We studied a flowing nitrogen DC discharge by Langmuir double probes and optical emission spectro... more We studied a flowing nitrogen DC discharge by Langmuir double probes and optical emission spectroscopy (OES). We measured the reduced electric field (E/N) and electron density (ne) with the double probes. The gas (Tg) and N2(X 1 Σ + g) vibrational temperature (θ) were measured by OES from the nitrogen first and second positive systems transitions. We constructed a kinetic numerical model accounting for N2(X 1 Σ + g, 0 ≤ v ≤ 45), N2(A 3 + u), N2(B 3 g), N2(a 1 g), N2(a' 1 - u), N2(w 1 Δu), N2(a'' 1 Σ + g),
Heat Pipe Science and Technology, An International Journal, 2015
This work describes the development of copper oxide multilayered porous media with 30 vol% of cha... more This work describes the development of copper oxide multilayered porous media with 30 vol% of charcoal, used as space holder material, which was milled during different time periods, 5 -45 minutes. A previews work developed with different space holder concentration showed that 30 vol% presents the best properties of mechanical resistance and porosity for the desired application and that each concentration presents a different percentage of retraction. In the present work, to be able to develop multilayer porous media, the concentration was maintained constant and the charcoal particle size was modified. The rheological behavior of the mixture was studied through constant rate curves. The ceramic bodies were produced in different layer combinations through aqueous colloidal processing, using slip casting as molding technique. The each layer final bodies were heat treated and characterized to obtain its porosity, pore size distribution, permeability and effective thermal conductivity. The sintered samples presented porosity of 60.2 ± 2,0 %, bimodal pore size distribution, permeability 10 -14 -10 -13 1/m 2 (depending of the space holder average particle size) and effective thermal conductivity of 5,6 W/(m⋅K). The multilayer porous media interface was characterized through scanning electron microscope images.
Exacta, 2009
A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repeti... more A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repetido a solda a frio e a fratura de partículas de pó em um moinho de alta energia. A técnica foi originalmente desenvolvida para produzir superligas reforçadas por óxidos dispersos para aplicações na indústria aeroespacial. Atualmente pode-se sintetizar uma grande variedade de ligas. Variáveis de processo e materiais de partida envolvidos na mecanossíntese são revisadas e discutidas neste artigo.
Effect of the metallic matrix on the sliding wear of plasma assisted debinded and sintered MIM self-lubricating steel
Wear, 2013
ABSTRACT A new processing route to obtain a homogeneous dispersion of discrete particles of solid... more ABSTRACT A new processing route to obtain a homogeneous dispersion of discrete particles of solid lubricant in the volume of sintered steels produced by metal injection moulding (MIM) was recently presented. In this technique, both thermal debinding and sintering are carried out in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. The homogeneous dispersion of discrete particles of solid lubricant was achieved by in situ formation of graphite nodules due to the dissociation of a precursor (SiC particles) mixed with the metallic matrix powders during the feedstock preparation. Nodules of graphite (size≤20 μm) presenting a nanostructured stacking of graphite foils with thickness of a few nanometres were obtained. In this work, the effect of the metallic matrix composition on the sliding wear behaviour (dry reciprocating sliding tests; normal load 7 N; frequency 2 Hz; stroke 10 mm; 5 mm diameter 52100 steel ball) of 3% SiC plasma assisted debinded and sintered (T=1150 °C, 1 h) self-lubricating steel is presented and discussed. Three different matrix compositions (Fe+0.6% C; Fe+0.6% C+4.0% Ni; Fe+0.6% C+4.0% Ni+1.0% Mo) were analysed. The mechanical properties were greatly increased by the addition of Nickel and further improved (2x) by the presence of Molybdenum. Increasing the hardness of the composites induced a strong decrease of the average friction coefficient, which reached values as low as 0.04. The counter body wear rate was greatly affected by the matrix composition (4x). Similar behaviour was observed for the wear rate of the specimen. The results were discussed in terms of wear mechanisms, which were characterised using SEM and micro Raman spectroscopy.
Surface and Coatings Technology, 2005
We report on the electrochemical stability of magnetron-sputtered Ti films on sintered and sinter... more We report on the electrochemical stability of magnetron-sputtered Ti films on sintered and sintered/plasma nitrided Fe -1.5% Mo alloy. Open-circuit potential and potentiodynamic polarization measurements were carried out in pH 7 saline solutions together with scanning electron microscopy imaging. Magnetron-sputtered Ti films on sintered samples were found to be gradually more electrochemically stable as the Ti deposition time increased from 20 to 60 min, characterized by open-circuit potential and potentiodynamic polarization measurements and SEM micrographs. Sintered/plasma nitrided+Ti samples, however, presented the best electrochemical stability for an intermediate deposition time of 30 min, while films deposited during 60 min were found to be more easily corroded, probably due to a decrease in the film-to-substrate adhesion because of the presence of a nitride layer prior to coating. In the case of sintered/plasma nitrided+Ti samples whose deposition time was 20 or 30 min, the effect of the two layers (nitride and Ti) was clearly greater than the sum of the individual effects, characterizing a synergistic effect.
Surface and Coatings Technology, 2001
The influence of pore size on the sealing of PrM superficial pores as a result of plasma nitrocar... more The influence of pore size on the sealing of PrM superficial pores as a result of plasma nitrocarburizing has been studied. Samples with different particle size distributions were sintered, resulting in surfaces with different pore sizes. The samples were compacted at 600 MPa and sintered at 1150ЊC for 1 h. The plasma treatment was carried out in an atmosphere of 87.75% N r9.75% H r2.5% CH for 2 h at three temperatures: 540; 570; and 600ЊC. The characteristics of the compound layer and 2 2 4 porosity sealing effect of unalloyed sintered iron has been evaluated as a function of treatment temperature. Sample Ž . characterization was carried out by means of standard optical metallographical techniques, scanning electron microscopy SEM and X-ray diffractometry. In order to quantify the presence of superficial pores on sintered iron and their sealing effect after plasma nitrocarburizing, image analysis was also performed. Plasma treatment resulted in a significant sealing of the pores, which is related with the compound layer formation.
Powder Metallurgy, 2001
tribological conditions, differences in wear rate as Pembroke Street, Cambridge, CB2 3QZ, UK, hig... more tribological conditions, differences in wear rate as Pembroke Street, Cambridge, CB2 3QZ, UK, high as seven times were found. Additionally they showed Dr Binder was at Empresa Brasileira de Comthat porosity has no significant effect on friction coefficient. pressores S.A.
The influence of ion energy bombardment on the surface porosity of plasma sintered iron
Materials Science and Engineering: A, 2003
ABSTRACT Unalloyed iron samples were sintered in the presence of a glow discharge, generated in a... more ABSTRACT Unalloyed iron samples were sintered in the presence of a glow discharge, generated in a gas mixture of 80% Ar+20% H2 at pressures ranging from 665 to 2660 Pa (5–20 Torr). Two configurations were used to carry out the plasma sintering. In the first one, the sample was placed on a holder, which worked as the cathode of the discharge, and was heated by the bombardment of ions, strongly accelerated in the cathode sheath. Confined anode–cathode geometry was used in the second configuration, in which the sample was placed onto the anode and heated by radiation from the cathode. In the cathode configuration, it was shown, that by changing the gas pressure from 2660 to 665 Pa, the energy of the ions bombarding the sample is increased by a factor of 3.8, with a corresponding increment of surface density. On the other hand, using the sample as anode, the surface porosity remained constant as a function of the gas discharge pressure and was higher than the porosity measured using the cathode configuration. The surface sealing of the plasma sintered sample subjected to the cathode configuration is attributed to the ion bombardment, which produced a high mobility of surface atoms and consequent enhanced diffusion as well as sputtering and condensation on the concave surface, resulting in an activation of surface sintering.
Materials Science and Engineering: A, 2005
Results of binder removal of injected PM components using plasma technology are presented. The sa... more Results of binder removal of injected PM components using plasma technology are presented. The samples were injected with 55.18 vol.% of iron powder, 23.57 vol.% of paraffin and 21.25 vol.%. of polypropylene and treated in hydrogen and argon discharges at a pressure of 400 Pa (3 Torr), varying temperature and treatment times. The discharge was generated by a pulsed power source in a confined anode-cathode geometry. The outer electrode consisted of the cathode and was heated by the bombardment of ions accelerated in the cathode region. The sample was placed on an inner holder and heated by thermal radiation. Three different configurations of electrodes were used in order to evaluate the influence of electron bombardment on the sample surface, the interaction of the reactive species generated in the discharge with the binder and thermal effects on the dissociation of the organic molecules. Samples were characterized by mass loss and energy dispersive X-ray (EDX) analysis. The results show that the electron bombardment added to the interaction of reactive species on the sample surface significantly activated the binder removal. By using a laboratory scale plasma reactor, it was shown that the binder extraction and pre-sintering cycle could be performed in a single thermal cycle lasting approximately 200 min.
Materials Science and Engineering: A, 2005
Sintering of unalloyed iron samples was performed in an abnormal glow discharge using a confined ... more Sintering of unalloyed iron samples was performed in an abnormal glow discharge using a confined anode-cathode configuration. The samples were placed on a holder acting as the discharge anode, inside a hollow cathode. The cathode was heated by the bombardment of ions and fast neutrals accelerated in the cathode sheath and as a consequence of the confined geometry the sample was efficiently heated by thermal radiation. In addition, the bombardment of the surface cathode by energetic particles produces sputtering of atoms, which by diffusion in the gas phase deposit on the sample surface. During sintering the deposited atoms diffuse into the solid sample, resulting in a layer enriched with elements sputtered out from the cathode. Two different cathode materials, no chromium steel and a chromium containing steel, were used in order to evince the influence of chromium element on the sintering process. It was observed that depending on the ion energy bombardment of the stainless steel cathode, more than 10% in weight of chromium was deposited on the sample surface, which resulted in the stabilization of the alpha phase of iron at the treatment temperature. In this condition, as the diffusion coefficient in the ␣-phase of iron is about 10 2 times higher than in the ␥-phase, the sintering of this enriched phase is activated. A layer about 20 m thick containing approximately 10 wt% of chromium was obtained after 1.0 h processing time.
Corrosion study of plasma sintered unalloyed iron: The influence of porosity sealing and Ni surface enrichment
Materials Science and Engineering: A, 2007
ABSTRACT Results of corrosion tests on samples produced by powder metallurgy technique are presen... more ABSTRACT Results of corrosion tests on samples produced by powder metallurgy technique are presented. Unalloyed iron samples were compacted at 600 MPa and sintered in a plasma reactor for 1 h at 1150 °C. Sintering was performed in an abnormal glow discharge generated in argon/hydrogen gas mixture using two different electrode configurations. In the first one, the sample acted as the discharge cathode (cathode configuration), being bombarded by energetic ions and fast neutrals. In this geometry, direct heating of the sample is provided by the bombardment of energetic particles. In addition, the bombardment of the sample surface by energetic particles resulted in an improvement of mass transport by volume diffusion and surface diffusion in the sample near to bombarded surface. As a consequence of the shrinkage due to sintering is higher in the outer volume layer of the sample resulting in surface porosity sealing. In the second configuration, the sample was placed on the anode of the discharge (anode configuration), inside a nickel hollow cathode. In this case the heating up of the sample is then obtained by radiation from the cathode. As a consequence of the bombardment of the nickel cathode, Ni atoms sputtered from the cathode were deposited on the sample surface resulting in an enriched Ni layer during the sintering process. Microstructure characterization and chemical composition were performed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD). Conventional electrochemical potentiodynamic tests were carried out in a 0.5 M KNO3 solution. The surface porosity reduction obtained in cathode configuration resulted in an increment of corrosion resistance. The superficial Ni enrichment obtained by sintering samples using the anode configuration was not sufficiently homogeneous to improve corrosion resistance.
Journal of Materials Science, 2007
Sub micrometer hollow metallic spheres of Ni-P alloy were produced in aqueous solutions at 80 °C ... more Sub micrometer hollow metallic spheres of Ni-P alloy were produced in aqueous solutions at 80 °C by chemical reduction over vesicle templates formed by selfassembling of sodium dodecyl sulfate (SDS) amphiphilic molecules. By varying the pH and SDS concentration (maintaining carefully fixed all other parameters) we obtain different sizes and size distributions, in a monomodal or sometimes bimodal regime. The higher the bath pH the lower the sphere sizes. The sphere shells are nanostructured and the higher the phosphorus content the lower the crystallite sizes. Mass density was of only 3.8 g/cm 3 as a consequence of the hollow morphology and nanostructure. These sphere shells are promising candidates for hydrodesulphurization catalyst due to their high specific area and chemical resistance to sulfur. Characterization was made by XRD, SEM, EDX and thermal analysis.
Grain size and surface roughness effect on the instability strains in sheet metal stretching
Journal of Materials Processing Technology, 2005
This paper examines the influence of surface roughness which is related directly to the grain siz... more This paper examines the influence of surface roughness which is related directly to the grain size to the onset of plastic instability and necking conditions. A theoretical analysis is presented of thickness and grain size dependence on the limit strains in the process of stretch forming of anisotropic thin sheet metals. The theory assumes that the roughness can be represented
Journal of Materials Processing Technology, 2006
The objective of the paper is to present a general algorithm that enables, in a simple way, the i... more The objective of the paper is to present a general algorithm that enables, in a simple way, the incorporation of a set of well known elasto-plastic constitutive models, for porous sintered materials, and to perform a comparative analysis of these various models. These models were modified in order to incorporate an isotropic work hardening and a porosity coupling behavior and implemented in the ABAQUS @ finite element program. The proposed algorithm considered an operator split technique which decomposed the problem into an elastic predictor followed, if necessary, by a plastic corrector step. The algorithm is presented in a general frame work and is thereafter particularized for a given set of constitutive models for porous sintered materials. In the work is also implemented some of these published elasto-plastic models that have not been implemented previously into FEM programs. Finally, some simple examples are solved with the aim of comparing the performance of these different models.
International Journal of Machine Tools and Manufacture, 2004
The subject of this paper is to analyze the impact of projectiles against ceramic/metal armour us... more The subject of this paper is to analyze the impact of projectiles against ceramic/metal armour using a simple one-dimensional mode. The model allows the calculation of the loss of projectile mass and its velocity, and gives the deflection of the backup material. This work also investigates the influence of grain size of the ceramic material on ballistic performance, which is very useful during selection of the best material for each application. Therefore, two formulations of the same ceramic material were produced. They had the same chemical composition, the same mechanical properties, but different grain size. The ballistic performances were compared measuring the maximum velocity each formulation was able to support, without perforation.
Materia-rio De Janeiro, Sep 1, 2014
the extraction process, resulting in the need to optimize the extraction cycle and thermal sinter... more the extraction process, resulting in the need to optimize the extraction cycle and thermal sintering. Slower cycles and low temperature promoted the complete extraction of the ligands. The Ni-Fe-Cr-P alloy injected showed shrinkage of approximately 50%, and high levels of pores as compared to the compacted material, which influenced the mechanical properties and apparent hardness of the material.
Bulletin of the American Physical Society, Mar 1, 2012
In order to obtain components with improved properties, several alternative techniques, based on ... more In order to obtain components with improved properties, several alternative techniques, based on plasma technology, have been studied. Surface porosity of plain iron could be modified by using plasma sintering. In this work, components produced by PM were sintered on a plasma reactor in the presence of an abnormal glow discharge. Two samples were produced using particles with different range size. One set of samples were produced with the full range of size of the powder (20-200 μm) with mean diameter of 100 μm. Another set of samples were produced using fractioned powder, with particle size fewer than 45 μm. Studies were carried out in order to evaluate the influence of ion energy bombardment and the particle sizes, on the surface porosity and tribological behaviour.
International Journal of Knowledge Engineering and Management, 2020
ANÁLISE DO FLUXO DE CONHECIMENTO NO NÍVEL DOS INDIVÍDUOS EM COLABORAÇÕES UNIVERSIDADE-INDÚSTRIA R... more ANÁLISE DO FLUXO DE CONHECIMENTO NO NÍVEL DOS INDIVÍDUOS EM COLABORAÇÕES UNIVERSIDADE-INDÚSTRIA Resumo Objetivo: Caracterizar o fluxo de conhecimento em colaborações universidadeindústria, no nível dos indivíduos, identificando os fatores que facilitam e dificultam o fluxo. DesignMetodologiaAbordagem: O estudo investiga o fenômeno a partir de uma perspectiva qualitativa, por meio de entrevistas semi-estruturadas e análise temática. Resultados: Apresentou-se uma representação para descrever o fluxo do conhecimento em colaborações universidade-indústria, no nível dos pesquisadores, como um processo iterativo em níveis e etapas. Identificou-se que um dos componentes chave para o fluxo são as interações entre pesquisadores de diferentes níveis e que disponibilidade, distância, contexto e a atuação de intermediadores influenciam a realização destas interações. OriginalidadeValor: Poucos estudos analisam o fluxo de conhecimento no nível dos indivíduos (micro nível). O trabalho evidenciou a importância da análise de fluxo de conhecimento no micro nível, mostrando aos gestores de colaboração universidadeindústria que é fundamental garantir a participação dos diferentes pesquisadores nos vários níveis de interação.
Brazilian Journal of Physics, 2020
We investigated flowing N 2 DC discharges both experimentally and theoretically. The discharge ga... more We investigated flowing N 2 DC discharges both experimentally and theoretically. The discharge gas and N 2 (X 1 Σ + g ) vibrational temperatures, electron density (n e ), reduced electric field (E/N), and radiative state densities were measured by optical emission spectrometry (OES) and Langmuir double probes. We formulated a discharge kinetic numerical model to calculate the densities of nitrogen species as functions of the gas residence time. We combine the experimental parameters measured in the discharge with the kinetic model to analyze different discharge conditions where E/N varies significantly. First, we analyzed the measured and calculated radiative states densities and N 2 (X 1 Σ + g ) vibrational distributions at the end of the positive column. Results show good agreement between calculated and measured parameters. Then, we studied the excited molecular species densities, and neutral and excited atoms densities as functions of the discharge gas residence time. This work presents for the first time the temporal densities of excited molecular and atomic states from 10 -9 to 10 -1 s discharge residence times, calculated for experimental conditions where n e presents a low variation and E/N varies from high (94 Td) to relatively low values (48 Td). The discharge experimental conditions are discharge current of 60 mA, gas pressure of 230-530 Pa, and gas flow rate of 0.9 Slm -1 . Neutral and excited atoms density . Neutral and excited molecule density . Nitrogen flowing discharges * Jacques Levaton
Plasma Research Express, 2019
We studied a flowing nitrogen DC discharge by Langmuir double probes and optical emission spectro... more We studied a flowing nitrogen DC discharge by Langmuir double probes and optical emission spectroscopy (OES). We measured the reduced electric field (E/N) and electron density (ne) with the double probes. The gas (Tg) and N2(X 1 Σ + g) vibrational temperature (θ) were measured by OES from the nitrogen first and second positive systems transitions. We constructed a kinetic numerical model accounting for N2(X 1 Σ + g, 0 ≤ v ≤ 45), N2(A 3 + u), N2(B 3 g), N2(a 1 g), N2(a' 1 - u), N2(w 1 Δu), N2(a'' 1 Σ + g),
Heat Pipe Science and Technology, An International Journal, 2015
This work describes the development of copper oxide multilayered porous media with 30 vol% of cha... more This work describes the development of copper oxide multilayered porous media with 30 vol% of charcoal, used as space holder material, which was milled during different time periods, 5 -45 minutes. A previews work developed with different space holder concentration showed that 30 vol% presents the best properties of mechanical resistance and porosity for the desired application and that each concentration presents a different percentage of retraction. In the present work, to be able to develop multilayer porous media, the concentration was maintained constant and the charcoal particle size was modified. The rheological behavior of the mixture was studied through constant rate curves. The ceramic bodies were produced in different layer combinations through aqueous colloidal processing, using slip casting as molding technique. The each layer final bodies were heat treated and characterized to obtain its porosity, pore size distribution, permeability and effective thermal conductivity. The sintered samples presented porosity of 60.2 ± 2,0 %, bimodal pore size distribution, permeability 10 -14 -10 -13 1/m 2 (depending of the space holder average particle size) and effective thermal conductivity of 5,6 W/(m⋅K). The multilayer porous media interface was characterized through scanning electron microscope images.
Exacta, 2009
A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repeti... more A mecanossíntese é uma técnica de processamento de pós no estado sólido envolvendo de modo repetido a solda a frio e a fratura de partículas de pó em um moinho de alta energia. A técnica foi originalmente desenvolvida para produzir superligas reforçadas por óxidos dispersos para aplicações na indústria aeroespacial. Atualmente pode-se sintetizar uma grande variedade de ligas. Variáveis de processo e materiais de partida envolvidos na mecanossíntese são revisadas e discutidas neste artigo.
Effect of the metallic matrix on the sliding wear of plasma assisted debinded and sintered MIM self-lubricating steel
Wear, 2013
ABSTRACT A new processing route to obtain a homogeneous dispersion of discrete particles of solid... more ABSTRACT A new processing route to obtain a homogeneous dispersion of discrete particles of solid lubricant in the volume of sintered steels produced by metal injection moulding (MIM) was recently presented. In this technique, both thermal debinding and sintering are carried out in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. The homogeneous dispersion of discrete particles of solid lubricant was achieved by in situ formation of graphite nodules due to the dissociation of a precursor (SiC particles) mixed with the metallic matrix powders during the feedstock preparation. Nodules of graphite (size≤20 μm) presenting a nanostructured stacking of graphite foils with thickness of a few nanometres were obtained. In this work, the effect of the metallic matrix composition on the sliding wear behaviour (dry reciprocating sliding tests; normal load 7 N; frequency 2 Hz; stroke 10 mm; 5 mm diameter 52100 steel ball) of 3% SiC plasma assisted debinded and sintered (T=1150 °C, 1 h) self-lubricating steel is presented and discussed. Three different matrix compositions (Fe+0.6% C; Fe+0.6% C+4.0% Ni; Fe+0.6% C+4.0% Ni+1.0% Mo) were analysed. The mechanical properties were greatly increased by the addition of Nickel and further improved (2x) by the presence of Molybdenum. Increasing the hardness of the composites induced a strong decrease of the average friction coefficient, which reached values as low as 0.04. The counter body wear rate was greatly affected by the matrix composition (4x). Similar behaviour was observed for the wear rate of the specimen. The results were discussed in terms of wear mechanisms, which were characterised using SEM and micro Raman spectroscopy.
Surface and Coatings Technology, 2005
We report on the electrochemical stability of magnetron-sputtered Ti films on sintered and sinter... more We report on the electrochemical stability of magnetron-sputtered Ti films on sintered and sintered/plasma nitrided Fe -1.5% Mo alloy. Open-circuit potential and potentiodynamic polarization measurements were carried out in pH 7 saline solutions together with scanning electron microscopy imaging. Magnetron-sputtered Ti films on sintered samples were found to be gradually more electrochemically stable as the Ti deposition time increased from 20 to 60 min, characterized by open-circuit potential and potentiodynamic polarization measurements and SEM micrographs. Sintered/plasma nitrided+Ti samples, however, presented the best electrochemical stability for an intermediate deposition time of 30 min, while films deposited during 60 min were found to be more easily corroded, probably due to a decrease in the film-to-substrate adhesion because of the presence of a nitride layer prior to coating. In the case of sintered/plasma nitrided+Ti samples whose deposition time was 20 or 30 min, the effect of the two layers (nitride and Ti) was clearly greater than the sum of the individual effects, characterizing a synergistic effect.
Surface and Coatings Technology, 2001
The influence of pore size on the sealing of PrM superficial pores as a result of plasma nitrocar... more The influence of pore size on the sealing of PrM superficial pores as a result of plasma nitrocarburizing has been studied. Samples with different particle size distributions were sintered, resulting in surfaces with different pore sizes. The samples were compacted at 600 MPa and sintered at 1150ЊC for 1 h. The plasma treatment was carried out in an atmosphere of 87.75% N r9.75% H r2.5% CH for 2 h at three temperatures: 540; 570; and 600ЊC. The characteristics of the compound layer and 2 2 4 porosity sealing effect of unalloyed sintered iron has been evaluated as a function of treatment temperature. Sample Ž . characterization was carried out by means of standard optical metallographical techniques, scanning electron microscopy SEM and X-ray diffractometry. In order to quantify the presence of superficial pores on sintered iron and their sealing effect after plasma nitrocarburizing, image analysis was also performed. Plasma treatment resulted in a significant sealing of the pores, which is related with the compound layer formation.
Powder Metallurgy, 2001
tribological conditions, differences in wear rate as Pembroke Street, Cambridge, CB2 3QZ, UK, hig... more tribological conditions, differences in wear rate as Pembroke Street, Cambridge, CB2 3QZ, UK, high as seven times were found. Additionally they showed Dr Binder was at Empresa Brasileira de Comthat porosity has no significant effect on friction coefficient. pressores S.A.
The influence of ion energy bombardment on the surface porosity of plasma sintered iron
Materials Science and Engineering: A, 2003
ABSTRACT Unalloyed iron samples were sintered in the presence of a glow discharge, generated in a... more ABSTRACT Unalloyed iron samples were sintered in the presence of a glow discharge, generated in a gas mixture of 80% Ar+20% H2 at pressures ranging from 665 to 2660 Pa (5–20 Torr). Two configurations were used to carry out the plasma sintering. In the first one, the sample was placed on a holder, which worked as the cathode of the discharge, and was heated by the bombardment of ions, strongly accelerated in the cathode sheath. Confined anode–cathode geometry was used in the second configuration, in which the sample was placed onto the anode and heated by radiation from the cathode. In the cathode configuration, it was shown, that by changing the gas pressure from 2660 to 665 Pa, the energy of the ions bombarding the sample is increased by a factor of 3.8, with a corresponding increment of surface density. On the other hand, using the sample as anode, the surface porosity remained constant as a function of the gas discharge pressure and was higher than the porosity measured using the cathode configuration. The surface sealing of the plasma sintered sample subjected to the cathode configuration is attributed to the ion bombardment, which produced a high mobility of surface atoms and consequent enhanced diffusion as well as sputtering and condensation on the concave surface, resulting in an activation of surface sintering.
Materials Science and Engineering: A, 2005
Results of binder removal of injected PM components using plasma technology are presented. The sa... more Results of binder removal of injected PM components using plasma technology are presented. The samples were injected with 55.18 vol.% of iron powder, 23.57 vol.% of paraffin and 21.25 vol.%. of polypropylene and treated in hydrogen and argon discharges at a pressure of 400 Pa (3 Torr), varying temperature and treatment times. The discharge was generated by a pulsed power source in a confined anode-cathode geometry. The outer electrode consisted of the cathode and was heated by the bombardment of ions accelerated in the cathode region. The sample was placed on an inner holder and heated by thermal radiation. Three different configurations of electrodes were used in order to evaluate the influence of electron bombardment on the sample surface, the interaction of the reactive species generated in the discharge with the binder and thermal effects on the dissociation of the organic molecules. Samples were characterized by mass loss and energy dispersive X-ray (EDX) analysis. The results show that the electron bombardment added to the interaction of reactive species on the sample surface significantly activated the binder removal. By using a laboratory scale plasma reactor, it was shown that the binder extraction and pre-sintering cycle could be performed in a single thermal cycle lasting approximately 200 min.
Materials Science and Engineering: A, 2005
Sintering of unalloyed iron samples was performed in an abnormal glow discharge using a confined ... more Sintering of unalloyed iron samples was performed in an abnormal glow discharge using a confined anode-cathode configuration. The samples were placed on a holder acting as the discharge anode, inside a hollow cathode. The cathode was heated by the bombardment of ions and fast neutrals accelerated in the cathode sheath and as a consequence of the confined geometry the sample was efficiently heated by thermal radiation. In addition, the bombardment of the surface cathode by energetic particles produces sputtering of atoms, which by diffusion in the gas phase deposit on the sample surface. During sintering the deposited atoms diffuse into the solid sample, resulting in a layer enriched with elements sputtered out from the cathode. Two different cathode materials, no chromium steel and a chromium containing steel, were used in order to evince the influence of chromium element on the sintering process. It was observed that depending on the ion energy bombardment of the stainless steel cathode, more than 10% in weight of chromium was deposited on the sample surface, which resulted in the stabilization of the alpha phase of iron at the treatment temperature. In this condition, as the diffusion coefficient in the ␣-phase of iron is about 10 2 times higher than in the ␥-phase, the sintering of this enriched phase is activated. A layer about 20 m thick containing approximately 10 wt% of chromium was obtained after 1.0 h processing time.
Corrosion study of plasma sintered unalloyed iron: The influence of porosity sealing and Ni surface enrichment
Materials Science and Engineering: A, 2007
ABSTRACT Results of corrosion tests on samples produced by powder metallurgy technique are presen... more ABSTRACT Results of corrosion tests on samples produced by powder metallurgy technique are presented. Unalloyed iron samples were compacted at 600 MPa and sintered in a plasma reactor for 1 h at 1150 °C. Sintering was performed in an abnormal glow discharge generated in argon/hydrogen gas mixture using two different electrode configurations. In the first one, the sample acted as the discharge cathode (cathode configuration), being bombarded by energetic ions and fast neutrals. In this geometry, direct heating of the sample is provided by the bombardment of energetic particles. In addition, the bombardment of the sample surface by energetic particles resulted in an improvement of mass transport by volume diffusion and surface diffusion in the sample near to bombarded surface. As a consequence of the shrinkage due to sintering is higher in the outer volume layer of the sample resulting in surface porosity sealing. In the second configuration, the sample was placed on the anode of the discharge (anode configuration), inside a nickel hollow cathode. In this case the heating up of the sample is then obtained by radiation from the cathode. As a consequence of the bombardment of the nickel cathode, Ni atoms sputtered from the cathode were deposited on the sample surface resulting in an enriched Ni layer during the sintering process. Microstructure characterization and chemical composition were performed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD). Conventional electrochemical potentiodynamic tests were carried out in a 0.5 M KNO3 solution. The surface porosity reduction obtained in cathode configuration resulted in an increment of corrosion resistance. The superficial Ni enrichment obtained by sintering samples using the anode configuration was not sufficiently homogeneous to improve corrosion resistance.
Journal of Materials Science, 2007
Sub micrometer hollow metallic spheres of Ni-P alloy were produced in aqueous solutions at 80 °C ... more Sub micrometer hollow metallic spheres of Ni-P alloy were produced in aqueous solutions at 80 °C by chemical reduction over vesicle templates formed by selfassembling of sodium dodecyl sulfate (SDS) amphiphilic molecules. By varying the pH and SDS concentration (maintaining carefully fixed all other parameters) we obtain different sizes and size distributions, in a monomodal or sometimes bimodal regime. The higher the bath pH the lower the sphere sizes. The sphere shells are nanostructured and the higher the phosphorus content the lower the crystallite sizes. Mass density was of only 3.8 g/cm 3 as a consequence of the hollow morphology and nanostructure. These sphere shells are promising candidates for hydrodesulphurization catalyst due to their high specific area and chemical resistance to sulfur. Characterization was made by XRD, SEM, EDX and thermal analysis.
Grain size and surface roughness effect on the instability strains in sheet metal stretching
Journal of Materials Processing Technology, 2005
This paper examines the influence of surface roughness which is related directly to the grain siz... more This paper examines the influence of surface roughness which is related directly to the grain size to the onset of plastic instability and necking conditions. A theoretical analysis is presented of thickness and grain size dependence on the limit strains in the process of stretch forming of anisotropic thin sheet metals. The theory assumes that the roughness can be represented