Nelson Lima - Academia.edu (original) (raw)

Papers by Nelson Lima

Materials Science Forum, 2015

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, how... more Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, however, it can present accelerated tetragonal to monoclinic phase transformation in oral environment. The aim of this study was to compare the behavior of a Y-TZP synthesized in laboratory by the coprecipitation method to a commercial Y-TZP, after hydrothermal aging in pressurized reactor (150°C/ 35 hours). The discs were sintered at 1520°C for two hours. The kinetics curve of phase transformation was determined through the data collect by XRD diffractograms treated by the Rietveld method. The experimental and commercial control groups did not present monoclinic phase. After 35 hours of aging, the experimental group presented 69% of monoclinic phase compared to 67% for the commercial group. Scanning electron microscopy and atomic force microscopy images suggested that the commercial group presented heterogeneity of grain size and that the experimental group was more homogeneous. All groups...

Rem: Revista Escola de Minas, 2007

O Efeito de Memória de Forma em ligas inoxidáveis está associado à transformação martensítica não... more 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.

Rem: Revista Escola de Minas, 2012

Nesse trabalho, foram estudados aspectos cinéticos da transformação bainítica incompleta em ligas... more 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 t...

Rem: Revista Escola de Minas, 2008

A evolução da textura, nos estados "como recebido", laminado a frio, recozido e após a ... more 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 p...

Materials Science Forum, 2012

Alumina and zirconia-alumina composite has been micro-structured in air using femtosecond laser. ... more Alumina and zirconia-alumina composite has been micro-structured in air using femtosecond laser. The threshold fluence of 6.2 J.cm-2 found in this work is close to that found published in literature [1]. In the case of Al-Zr, the threshold fluence is 2.2 J.cm-2 .Surface femtosecond laser treatment increase the apatite deposition by biomimetic method on alumina and alumina-zirconia composite and depends on the condition of laser treatments.

Surface and Coatings Technology, 2010

The aim of the present work was to study the corrosion resistance in Hanks' solution and the in v... more The aim of the present work was to study the corrosion resistance in Hanks' solution and the in vitro biocompatibility of a TiCN-coated AISI 316 L stainless steel. The electrochemical behavior was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy. Cytotoxicity and genotoxicity tests were performed to evaluate the potential biocompatibility of the specimens. TiCN morphology was investigated using scanning electron microscopy (SEM). Bare 316 L specimens were also evaluated for comparison. The results showed that the film morphology strongly influences the electrochemical behavior of the coated underlying metal. TiCN-coated specimens presented neither cytotoxicity nor genotoxicity.

Surface and Coatings Technology, 2010

In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrat... more In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrates were conducted in a Triode Magnetron Sputtering chamber. The temperature; gas flow and pressure were kept constant during each run. The substrate bias was either decreased or increased in a sequence of steps. Residual stress measurements were later conducted through the grazing X-ray diffraction method. Different incident angles were used in order to change the penetration depth and to obtain values of residual stress at different film depths. A model described by Dolle was adapted as an attempt to calculate the values of residual stress at each incident angle as a function of the value from each individual layer. Stress results indicated that the decrease in bias voltage during the deposition has produced compressive residual stress gradients through the film thickness. On the other hand, much less pronounced gradients were found in one of the films deposited with increasing bias voltage.

Journal of Magnetism and Magnetic Materials, 2004

In this study, magnetic domains in Pr 16 Fe 76 B 8 sintered magnets have been observed by Kerr ef... more In this study, magnetic domains in Pr 16 Fe 76 B 8 sintered magnets have been observed by Kerr effect and a histogram of the angular distribution of domain orientations has been used to determine the magnetic texture ð/cos FSÞ: The degree of easy-axis alignment of Pr 2 Fe 14 B matrix grains in these magnets has been also determined by X-ray pole figure analysis using the (0 0 4) reflection. The (0 0 4) pole figure measurements were carried out by the Schultz's reflection method. The (0 0 4) normalized intensity data has been fitted for a Gaussian distribution and the degree of crystal alignment, /cos YS; has been calculated using the Stoner-Wohlfarth model. Comparison of these methods has been carried out. It has been shown that in magnets with medium and high degrees of crystallographic alignment, the pole figure values are higher than that obtained by the Kerr effect method. Conversely, in magnets with low degrees of alignment, /cos YS is lower than /cos FS:

Purpose: Purpose of this paper was to study the main effects of the turning in the superficial in... more Purpose: Purpose of this paper was to study the main effects of the turning in the superficial integrity of the duplex stainless steel ASTM A890-Gr6A. Design/methodology/approach: The focus of the work was the finishing operations and a complete factorial planning was used, with 2 levels and 5 factors. The tests were conducted on a turning center with carbide tools and the main entrances variables were: tool material class, feed rate, cutting depth, cutting speed and cutting fluid utilization. The answers analyzed were: micro structural analysis by optical microscopy and x-ray diffraction, cutting forces measurements by a piezoelectric dynamometer, surface roughness, residual stress by x-ray diffraction technique and the micro-hardness measurements. Findings: The results do not showed any changes in the micro structural of the material, even when the greater cutting parameters were used. All the other answers were correlated with the cutting parameters and its better combination was founded for the best superficial integrity. The smaller feed rate (0.1 mm/v), smaller cutting speed (110 m/min) and the greater cutting depth (0.5 mm) provided the smaller values for the tensile residual stress, the smaller surface roughness and the greater micro-hardness. Research limitations/implications: The correlation between all the answers was very difficult to analyze because there was great interaction between the factors, but for some data group it was possible. Originality/value: The paper contribute for the study of the super duplex stainless steel, considering that no one researches was founded for the studied topics in this material in witch presents different behavior in machining when compared with another stainless steels.

ISIJ International, 2014

A mathematical model to calculate the build-up of residual stresses during quenching of carbon (A... more A mathematical model to calculate the build-up of residual stresses during quenching of carbon (AISI 1045) and low-alloy (AISI 4140 and 4340) cylindrical steel bars is proposed. The model is implemented as a combination of the commercial software AC3 ® , to simulate the microstructure evolution, and Abaqus ® , to model the heat transfer and the elastic, plastic, thermal, and phase transformation strains/stresses by the finite element method. All steel properties required in the model are calculated as an average of the properties of individual microconstituents (austenite, pearlite, bainite, or martensite) weighted by their local volume fractions, enabling the model application to any type of carbon or low-alloy steel. To thoroughly verify the simulation results, experimental measurements were carried out in cylindrical bars quenched in stirred water and these measurements were compared with model results. The heat transfer coefficient between the bar and the water was calculated by an inverse solution technique, resulting in the constant value of 7 200 W m-2 K-1 for the whole quenching period. For the low-alloy steels, measured and calculated volume fractions of martensite in the bar cross sections are in very good agreement, but for the carbon steel, large discrepancies are observed in the fractions of most constituents. Tangential and axial residual stresses were measured on the lateral surface of the quenched bars using the X-ray diffraction method. These stresses, which are compressive, agree well with those calculated by the present model, showing discrepancies generally lower than 10%.

Materials & Design, 2013

Improvement of fatigue life in parts subjected to cyclic stresses by application of mechanical su... more Improvement of fatigue life in parts subjected to cyclic stresses by application of mechanical surface treatment processes is already well known, both in the industry and in the academy. Dealing with automotive springs, the shot peening process becomes an essential step in manufacturing. In the case of leaf springs, however, a systematic investigation of the effect of shot peening on fatigue life is still required. The aim of the present work is to improve the knowledge on the role of shot peening in manufacturing leaf springs for vehicles, through the analysis of residual stresses by X-ray diffraction and fatigue tests on a series of samples that were subject to ten different peening schedules. Among the investigated processes, the usage of 0.8 mm diameter cast steel shot followed by a second peening with 0.3 mm diameter cast steel shot leads to optimal performance, regarding fatigue life. X-ray diffraction analysis shows that this improved performance may be attributed to residual compressive stress maintained until a depth of 0.02 mm below the surface, which directly influences fatigue crack nucleation. Residual stresses induced by shot peening in larger depths have no influence on the sample's fatigue life.

Materials Science Forum, 2006

A process for synthesis of fine zirconium titanate powders by chemical route is described. Zircon... more A process for synthesis of fine zirconium titanate powders by chemical route is described. Zirconium/titanium molar ratio was varied from 0.67 to 1.5 and the powders produced were analyzed. The precipitation process comprises the mixture of zirconium and titanium metal salt solutions to ammonium hydroxide solution, followed by washing of the precipitate, calcination and grinding to result in zirconium titanate. The ceramic powder is then uniaxially pressed as cylindrical samples and sintered at 1400°C for 5 hours. The microstructure of fractured and thermally etched ceramic was observed by scanning electron microscopy, and crystal phase identifications were done by X-ray diffraction. At least two different zirconium titanate phases, ZrTiO 4 and Zr 5 Ti 7 O 24 , were identified. Ceramic hardness was measured by Vickers indentation.

Materials Science Forum, 2006

The addition of alumina in a zirconia stabilized in a tetragonal phase matrix enhances ceramic ha... more The addition of alumina in a zirconia stabilized in a tetragonal phase matrix enhances ceramic hardness and inhibits the tetragonal → monoclinic phase transformation of zirconia when exposed to an aqueous environment. These characteristics are important for applications such as bioceramics and structural materials. For these purposes, the strict control of powder synthesis and the processing conditions are vital to tailor the ceramic characteristics. This work evaluates the influence of 20 wt% alumina in a Y-TZP matrix on powder characteristics, obtained by coprecipitation route, and calcined from 600 to 1200°C for 1 and 3 hours. The powders obtained were characterized by X-ray diffraction, scanning electronic microscopy, laser diffraction and gaseous adsorption (BET). The results reveal that presence of Al3+ inhibits the crystallization of composite at lower temperatures.

Materials Science and Engineering: A, 2009

Medium carbon steels are mostly used for simple applications; nevertheless new applications have ... more Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7-80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the "as received", cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations.

Journal of Alloys and Compounds, 2009

Cubic stabilized zirconia is the preferred material for application as solid electrolyte in solid... more Cubic stabilized zirconia is the preferred material for application as solid electrolyte in solid oxide fuel cells. However, this material has low fracture toughness, which can lead to formation of cracks during long-term operation. Moreover, increase of mechanical as well as electrical properties would be useful for cost-effectiveness of this type of device. In this context, addition of alumina to zirconia-based solid electrolyte can be an interesting option to accomplish that purpose. In this work, ceramic composites containing various amounts of alumina in a 9 mol% yttria-stabilized zirconia matrix were synthesized by the coprecipitation route using a low-silica zirconium precursor. Characterization techniques included scanning electron microscopy, X-ray diffraction, Vickers hardness and impedance spectroscopy. As a consequence of optimization of the synthesis route a homogeneous dispersion of the additive along with good densification was obtained. Although alumina addition to stabilized zirconia exerts a deleterious effect on the electrical conductivity, it improves the Vickers hardness and fracture toughness of the composite materials.

Materials Research, 2005

Aluminium-silicon alloys have been wide accepted in the automotive, electric and aerospace indust... more 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.

Materials Science Forum, 2003

The gravimetric and voltametric methods for determination of non-stoichiometry O/U ratio in urani... more The gravimetric and voltametric methods for determination of non-stoichiometry O/U ratio in uranium dioxide used as nuclear fuel are evaluate in this work. The oxidation of uranium oxide is very complex due to many phase changes and the gravimetric and voltametric methods do not detect these phase changes. To evaluate both methods is requiring to do Rietveld methods by X-ray diffraction data to identify the uranium oxides phase changes. The results show that voltametric and gravimetric methods are precise but not accurate techniques for determination of non stoichiometry uranium dioxide samples.

Materials Science Forum, 2008

The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel h... more The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.

Materials Science Forum, 2003

The study of Sr-doped lanthanum manganites (La 1-x Sr x MnO 3 ) leads to solid oxide fuel cells (... more The study of Sr-doped lanthanum manganites (La 1-x Sr x MnO 3 ) leads to solid oxide fuel cells (SOFC) cathodic material application. This material has been studied due to its excelent electrochemical, chemical and thermical stability performance, futher electrolyte compatibility. This composition was prepared using traditional ceramic processing methods. The density about 93% of the theoretical was obtained for x = 0,5. The results obtained suggested that sintering temperature and type materials used for preparation powder of La 1-x Sr x MnO 3 could influence the sintered density and porosity of the sintered samples. Vickers microhardness measurements showed similar behaviour for the samples prepared with different purity degrees of La 2 O 3 .

Materials Science Forum, 2008

Zircon sand was reacted with liquid caustic soda (50% NaOH) in open vessel at 600 oC for 2h. The ... more Zircon sand was reacted with liquid caustic soda (50% NaOH) in open vessel at 600 oC for 2h. The effect of NaOH/ZrSiO4 reactant ratio on the yield of zirconia recovery was verified. Samples of fusion products water washed were characterized by X-ray diffraction (XRD) to identify the main compounds formed. Silica powders were obtained via acid catalyzed reaction and zirconia powders were resulted from crystallization of zirconium oxychoride. Both zirconia and silica powders were analyzed by XRF (X-ray fluorescence) and BET method. Laser Quasi Elastic Light Scattering (QLS) technique was used for agglomerate size distribution determination. High purity and fine zirconia and silica powders were obtained. The specific surface area of zirconia calcined at 550 oC reached ~ 70m2g-1. Silica powder calcined at 800 oC presented a high specific surface area ~ 500 m2g-1.

Materials Science Forum, 2015

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, how... more Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, however, it can present accelerated tetragonal to monoclinic phase transformation in oral environment. The aim of this study was to compare the behavior of a Y-TZP synthesized in laboratory by the coprecipitation method to a commercial Y-TZP, after hydrothermal aging in pressurized reactor (150°C/ 35 hours). The discs were sintered at 1520°C for two hours. The kinetics curve of phase transformation was determined through the data collect by XRD diffractograms treated by the Rietveld method. The experimental and commercial control groups did not present monoclinic phase. After 35 hours of aging, the experimental group presented 69% of monoclinic phase compared to 67% for the commercial group. Scanning electron microscopy and atomic force microscopy images suggested that the commercial group presented heterogeneity of grain size and that the experimental group was more homogeneous. All groups...

Rem: Revista Escola de Minas, 2007

O Efeito de Memória de Forma em ligas inoxidáveis está associado à transformação martensítica não... more 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.

Rem: Revista Escola de Minas, 2012

Nesse trabalho, foram estudados aspectos cinéticos da transformação bainítica incompleta em ligas... more 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 t...

Rem: Revista Escola de Minas, 2008

A evolução da textura, nos estados "como recebido", laminado a frio, recozido e após a ... more 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 p...

Materials Science Forum, 2012

Alumina and zirconia-alumina composite has been micro-structured in air using femtosecond laser. ... more Alumina and zirconia-alumina composite has been micro-structured in air using femtosecond laser. The threshold fluence of 6.2 J.cm-2 found in this work is close to that found published in literature [1]. In the case of Al-Zr, the threshold fluence is 2.2 J.cm-2 .Surface femtosecond laser treatment increase the apatite deposition by biomimetic method on alumina and alumina-zirconia composite and depends on the condition of laser treatments.

Surface and Coatings Technology, 2010

The aim of the present work was to study the corrosion resistance in Hanks' solution and the in v... more The aim of the present work was to study the corrosion resistance in Hanks' solution and the in vitro biocompatibility of a TiCN-coated AISI 316 L stainless steel. The electrochemical behavior was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy. Cytotoxicity and genotoxicity tests were performed to evaluate the potential biocompatibility of the specimens. TiCN morphology was investigated using scanning electron microscopy (SEM). Bare 316 L specimens were also evaluated for comparison. The results showed that the film morphology strongly influences the electrochemical behavior of the coated underlying metal. TiCN-coated specimens presented neither cytotoxicity nor genotoxicity.

Surface and Coatings Technology, 2010

In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrat... more In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrates were conducted in a Triode Magnetron Sputtering chamber. The temperature; gas flow and pressure were kept constant during each run. The substrate bias was either decreased or increased in a sequence of steps. Residual stress measurements were later conducted through the grazing X-ray diffraction method. Different incident angles were used in order to change the penetration depth and to obtain values of residual stress at different film depths. A model described by Dolle was adapted as an attempt to calculate the values of residual stress at each incident angle as a function of the value from each individual layer. Stress results indicated that the decrease in bias voltage during the deposition has produced compressive residual stress gradients through the film thickness. On the other hand, much less pronounced gradients were found in one of the films deposited with increasing bias voltage.

Journal of Magnetism and Magnetic Materials, 2004

In this study, magnetic domains in Pr 16 Fe 76 B 8 sintered magnets have been observed by Kerr ef... more In this study, magnetic domains in Pr 16 Fe 76 B 8 sintered magnets have been observed by Kerr effect and a histogram of the angular distribution of domain orientations has been used to determine the magnetic texture ð/cos FSÞ: The degree of easy-axis alignment of Pr 2 Fe 14 B matrix grains in these magnets has been also determined by X-ray pole figure analysis using the (0 0 4) reflection. The (0 0 4) pole figure measurements were carried out by the Schultz's reflection method. The (0 0 4) normalized intensity data has been fitted for a Gaussian distribution and the degree of crystal alignment, /cos YS; has been calculated using the Stoner-Wohlfarth model. Comparison of these methods has been carried out. It has been shown that in magnets with medium and high degrees of crystallographic alignment, the pole figure values are higher than that obtained by the Kerr effect method. Conversely, in magnets with low degrees of alignment, /cos YS is lower than /cos FS:

Purpose: Purpose of this paper was to study the main effects of the turning in the superficial in... more Purpose: Purpose of this paper was to study the main effects of the turning in the superficial integrity of the duplex stainless steel ASTM A890-Gr6A. Design/methodology/approach: The focus of the work was the finishing operations and a complete factorial planning was used, with 2 levels and 5 factors. The tests were conducted on a turning center with carbide tools and the main entrances variables were: tool material class, feed rate, cutting depth, cutting speed and cutting fluid utilization. The answers analyzed were: micro structural analysis by optical microscopy and x-ray diffraction, cutting forces measurements by a piezoelectric dynamometer, surface roughness, residual stress by x-ray diffraction technique and the micro-hardness measurements. Findings: The results do not showed any changes in the micro structural of the material, even when the greater cutting parameters were used. All the other answers were correlated with the cutting parameters and its better combination was founded for the best superficial integrity. The smaller feed rate (0.1 mm/v), smaller cutting speed (110 m/min) and the greater cutting depth (0.5 mm) provided the smaller values for the tensile residual stress, the smaller surface roughness and the greater micro-hardness. Research limitations/implications: The correlation between all the answers was very difficult to analyze because there was great interaction between the factors, but for some data group it was possible. Originality/value: The paper contribute for the study of the super duplex stainless steel, considering that no one researches was founded for the studied topics in this material in witch presents different behavior in machining when compared with another stainless steels.

ISIJ International, 2014

A mathematical model to calculate the build-up of residual stresses during quenching of carbon (A... more A mathematical model to calculate the build-up of residual stresses during quenching of carbon (AISI 1045) and low-alloy (AISI 4140 and 4340) cylindrical steel bars is proposed. The model is implemented as a combination of the commercial software AC3 ® , to simulate the microstructure evolution, and Abaqus ® , to model the heat transfer and the elastic, plastic, thermal, and phase transformation strains/stresses by the finite element method. All steel properties required in the model are calculated as an average of the properties of individual microconstituents (austenite, pearlite, bainite, or martensite) weighted by their local volume fractions, enabling the model application to any type of carbon or low-alloy steel. To thoroughly verify the simulation results, experimental measurements were carried out in cylindrical bars quenched in stirred water and these measurements were compared with model results. The heat transfer coefficient between the bar and the water was calculated by an inverse solution technique, resulting in the constant value of 7 200 W m-2 K-1 for the whole quenching period. For the low-alloy steels, measured and calculated volume fractions of martensite in the bar cross sections are in very good agreement, but for the carbon steel, large discrepancies are observed in the fractions of most constituents. Tangential and axial residual stresses were measured on the lateral surface of the quenched bars using the X-ray diffraction method. These stresses, which are compressive, agree well with those calculated by the present model, showing discrepancies generally lower than 10%.

Materials & Design, 2013

Improvement of fatigue life in parts subjected to cyclic stresses by application of mechanical su... more Improvement of fatigue life in parts subjected to cyclic stresses by application of mechanical surface treatment processes is already well known, both in the industry and in the academy. Dealing with automotive springs, the shot peening process becomes an essential step in manufacturing. In the case of leaf springs, however, a systematic investigation of the effect of shot peening on fatigue life is still required. The aim of the present work is to improve the knowledge on the role of shot peening in manufacturing leaf springs for vehicles, through the analysis of residual stresses by X-ray diffraction and fatigue tests on a series of samples that were subject to ten different peening schedules. Among the investigated processes, the usage of 0.8 mm diameter cast steel shot followed by a second peening with 0.3 mm diameter cast steel shot leads to optimal performance, regarding fatigue life. X-ray diffraction analysis shows that this improved performance may be attributed to residual compressive stress maintained until a depth of 0.02 mm below the surface, which directly influences fatigue crack nucleation. Residual stresses induced by shot peening in larger depths have no influence on the sample's fatigue life.

Materials Science Forum, 2006

A process for synthesis of fine zirconium titanate powders by chemical route is described. Zircon... more A process for synthesis of fine zirconium titanate powders by chemical route is described. Zirconium/titanium molar ratio was varied from 0.67 to 1.5 and the powders produced were analyzed. The precipitation process comprises the mixture of zirconium and titanium metal salt solutions to ammonium hydroxide solution, followed by washing of the precipitate, calcination and grinding to result in zirconium titanate. The ceramic powder is then uniaxially pressed as cylindrical samples and sintered at 1400°C for 5 hours. The microstructure of fractured and thermally etched ceramic was observed by scanning electron microscopy, and crystal phase identifications were done by X-ray diffraction. At least two different zirconium titanate phases, ZrTiO 4 and Zr 5 Ti 7 O 24 , were identified. Ceramic hardness was measured by Vickers indentation.

Materials Science Forum, 2006

The addition of alumina in a zirconia stabilized in a tetragonal phase matrix enhances ceramic ha... more The addition of alumina in a zirconia stabilized in a tetragonal phase matrix enhances ceramic hardness and inhibits the tetragonal → monoclinic phase transformation of zirconia when exposed to an aqueous environment. These characteristics are important for applications such as bioceramics and structural materials. For these purposes, the strict control of powder synthesis and the processing conditions are vital to tailor the ceramic characteristics. This work evaluates the influence of 20 wt% alumina in a Y-TZP matrix on powder characteristics, obtained by coprecipitation route, and calcined from 600 to 1200°C for 1 and 3 hours. The powders obtained were characterized by X-ray diffraction, scanning electronic microscopy, laser diffraction and gaseous adsorption (BET). The results reveal that presence of Al3+ inhibits the crystallization of composite at lower temperatures.

Materials Science and Engineering: A, 2009

Medium carbon steels are mostly used for simple applications; nevertheless new applications have ... more Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7-80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the "as received", cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations.

Journal of Alloys and Compounds, 2009

Cubic stabilized zirconia is the preferred material for application as solid electrolyte in solid... more Cubic stabilized zirconia is the preferred material for application as solid electrolyte in solid oxide fuel cells. However, this material has low fracture toughness, which can lead to formation of cracks during long-term operation. Moreover, increase of mechanical as well as electrical properties would be useful for cost-effectiveness of this type of device. In this context, addition of alumina to zirconia-based solid electrolyte can be an interesting option to accomplish that purpose. In this work, ceramic composites containing various amounts of alumina in a 9 mol% yttria-stabilized zirconia matrix were synthesized by the coprecipitation route using a low-silica zirconium precursor. Characterization techniques included scanning electron microscopy, X-ray diffraction, Vickers hardness and impedance spectroscopy. As a consequence of optimization of the synthesis route a homogeneous dispersion of the additive along with good densification was obtained. Although alumina addition to stabilized zirconia exerts a deleterious effect on the electrical conductivity, it improves the Vickers hardness and fracture toughness of the composite materials.

Materials Research, 2005

Aluminium-silicon alloys have been wide accepted in the automotive, electric and aerospace indust... more 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.

Materials Science Forum, 2003

The gravimetric and voltametric methods for determination of non-stoichiometry O/U ratio in urani... more The gravimetric and voltametric methods for determination of non-stoichiometry O/U ratio in uranium dioxide used as nuclear fuel are evaluate in this work. The oxidation of uranium oxide is very complex due to many phase changes and the gravimetric and voltametric methods do not detect these phase changes. To evaluate both methods is requiring to do Rietveld methods by X-ray diffraction data to identify the uranium oxides phase changes. The results show that voltametric and gravimetric methods are precise but not accurate techniques for determination of non stoichiometry uranium dioxide samples.

Materials Science Forum, 2008

The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel h... more The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.

Materials Science Forum, 2003

The study of Sr-doped lanthanum manganites (La 1-x Sr x MnO 3 ) leads to solid oxide fuel cells (... more The study of Sr-doped lanthanum manganites (La 1-x Sr x MnO 3 ) leads to solid oxide fuel cells (SOFC) cathodic material application. This material has been studied due to its excelent electrochemical, chemical and thermical stability performance, futher electrolyte compatibility. This composition was prepared using traditional ceramic processing methods. The density about 93% of the theoretical was obtained for x = 0,5. The results obtained suggested that sintering temperature and type materials used for preparation powder of La 1-x Sr x MnO 3 could influence the sintered density and porosity of the sintered samples. Vickers microhardness measurements showed similar behaviour for the samples prepared with different purity degrees of La 2 O 3 .

Materials Science Forum, 2008

Zircon sand was reacted with liquid caustic soda (50% NaOH) in open vessel at 600 oC for 2h. The ... more Zircon sand was reacted with liquid caustic soda (50% NaOH) in open vessel at 600 oC for 2h. The effect of NaOH/ZrSiO4 reactant ratio on the yield of zirconia recovery was verified. Samples of fusion products water washed were characterized by X-ray diffraction (XRD) to identify the main compounds formed. Silica powders were obtained via acid catalyzed reaction and zirconia powders were resulted from crystallization of zirconium oxychoride. Both zirconia and silica powders were analyzed by XRF (X-ray fluorescence) and BET method. Laser Quasi Elastic Light Scattering (QLS) technique was used for agglomerate size distribution determination. High purity and fine zirconia and silica powders were obtained. The specific surface area of zirconia calcined at 550 oC reached ~ 70m2g-1. Silica powder calcined at 800 oC presented a high specific surface area ~ 500 m2g-1.