Kátia Regina Cardoso - Academia.edu (original) (raw)
Papers by Kátia Regina Cardoso
Letters on Materials, 2018
Letters on Materials, 2018
Metals
In this study, we successfully obtained a 2Mg-Fe mixture through mechanical alloying (MA) and pro... more In this study, we successfully obtained a 2Mg-Fe mixture through mechanical alloying (MA) and processed it via accumulative roll bonding (ARB) (MA+ARB). Our primary focus was to analyze the impact of ambient air exposure while also evaluating the processing route. Some powder samples were exposed to air for 12 months (stored in a glass desiccator with an average yearly temperature and relative humidity of ~27 °C and 50.5%) before undergoing ARB processing. The Mg samples obtained after ARB processing exhibited a (002)-type texture. Our results demonstrate that all samples, including those processed via ARB, could rapidly absorb hydrogen within a matter of minutes despite considerable differences in surface area between powders and rolled samples. Grain size reduction by MA and ARB processing and texturing may have influenced this behavior. ARB-processed samples reached approximately 60% (~1.8 wt.%) of their maximum acquired capacity within just 24 min compared to powders (~2.2 wt.%)...
Journal of Materials Research, 2020
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Materials Science Forum, 2000
Many high-strength Al-based alloys have been developed recently after it was found that for certa... more Many high-strength Al-based alloys have been developed recently after it was found that for certain composition range, crystallisation from amorphous alloys could lead to a composite structure consisting of primary nanocrystals embedded in an amorphous matrix. However, even better values of mechanical strength,vas reported for Al-bused fully crystallised alloys with a composite structure formed by a mixture of primary nanocrystals and quasicrystalline phases therefore, the development of new compositions continues to be of interest. In the present work we report on the crystallisation behaviour of amorphous melt-spun Al-Fc-Nd-Cu alloys. Crystallisation was studied by differential scanning calorimetry and the characterisation of samples partially and fully crystallised was performed by X-ray diffraction and transmission electron microscopy. For the alloy Al85Fe4Nd6Cu5 crystallisation occurred by multiple stage with the first peak being associated with primary Al and two DSC peaks observed at higher temperatures have been associated with metastable phases. These results are discussed in association with the effect of the Cu content ill the crystallisation behaviour as compared with Al-Fe-Nd alloys.Univ Fed Sao Paulo, Dept Mat Engn, BR-13565905 Sao Carlos, SP, BrazilInst Natl Polytech Grenoble, CNRS, LTPCM, FR-38402 St Martin Dheres, FranceUniv Fed Sao Paulo, Dept Mat Engn, BR-13565905 Sao Carlos, SP, BrazilWeb of Scienc
Materials Science Forum, 2014
The AISI 52100 steel is a material widely used in the industry due to its high fatigue resistance... more The AISI 52100 steel is a material widely used in the industry due to its high fatigue resistance, dimensional stability, high hardness and wear resistance. This steel is used for production of ball bearings, stamping tools, etc. In case of production of ball bearings and its track this material is spherodized because, due to its high content of carbon, about 1%, it has high mechanical strength making it impossible to cold forming. To obtain a wear resistant surface, after forming, this material is hardened and tempered. Normally to obtain the AISI 52100 steel, arc electric melting furnace is used. This work aims the reuse of AISI 52100 steel by powder metallurgy route, starting from the machined chips using high energy mill (planetary) to obtain the powder. Then, the powder was uniaxially pressed into a press with a load of 4 tons, to form the specimen, later on pressed in an isostatic press at a pressure of 300MPa to obtain a better densification. To analyze the powder morphology ...
METALLIC …, 2005
After 80 h of milling the elemental powders, mechanical alloying of Al 90 Fe 5 Nd 5 produces a na... more After 80 h of milling the elemental powders, mechanical alloying of Al 90 Fe 5 Nd 5 produces a nanostructured composite, which consists of nanocrystals of fcc-Al and some Al 11 Nd 3 precipitates, embedded in an amorphous matrix. This composite has a Vickers hardness ...
ABM Proceedings, 2014
Resumo O aço inoxidável austenítico 316 (316 SS) é um dos materiais metálicos mais utilizados em ... more Resumo O aço inoxidável austenítico 316 (316 SS) é um dos materiais metálicos mais utilizados em aplicações médicas devido à combinação de propriedades mecânicas e do baixo custo. No entanto, desgaste e corrosão estimulam mudanças permanentes no tecido humano que podem levar à perda do implante. O desenvolvimento de recobrimentos biocompatíveis e estáveis, que apresentem propriedades mecânicas adequadas, e que não sofram ruptura ou delaminação durante o uso, é uma solução muito promissora para melhorar o desempenho do 316 SS como biomaterial para implantes. Neste trabalho, uma liga intermetálica FeAlCr, que tem apresentado propriedades adequadas para a aplicação como biomaterial, foi utilizada como recobrimento sobre um aço inoxidável 316 de grau médico. O revestimento foi obtido utilizando-se a técnica magnetron sputtering por corrente contínua. Os parâmetros de deposição, como distância substrato-alvo e pressão de gás argônio foram mantidos fixos em 50 mm e 5 mTorr, respectivamente. As amostras foram preparadas com os seguintes valores de potência de sputtering: 50 W, 75W, 100 W e 150 W. A adesão dos filmes foi analisada por teste de scratch, enquanto a espessura e a taxa de deposição foram analisadas por perfilometria ótica. As características estruturais foram analisadas por microscopia eletrônica de varredura com EDS. Palavras-chave: Sputtering; Aço inoxidável; Liga FeAlCr; Biomaterial DEPOSITION OF THIN FILMS OF INTERMETALLIC FeAlCr ALLOY BY SPUTTERING FOR BIOMATERIALS APPLICATION Abstract The 316 type austenitic stainless steel (316 SS) is one of the most used metallic materials in medical applications due to the combination of mechanical properties with low cost. However, wear and corrosion behavior stimulate permanent changes in human tissue that can lead to implant loss. The development of stable and biocompatible coatings presenting suitable mechanical properties and which does not undergo cracking or to peel off during the use is a very promising solution for improving the performance of 316 SS as biomaterials for implants. In this paper a coating based on an intermetallic FeAlCr alloy, material that have been presenting suitable properties for biomaterial application, was deposited on a 316 medical grade stainless steel. The coating was obtained by using a direct-current magnetron sputtering. During deposition the parameters substrate-target distance and argon gas pressure were fixed at 50mm and 5 mTorr, respectively. Samples were produced using the following sputtering power: 50 W, 75W, 100 W and 150 W. The films obtained were examined for adhesion to the substrate through the scratch test, while the thickness and deposition rate was analyzed by profilometry. Structural characteristics were evaluated by scanning electron microscopy with EDS
Materials Science and Technology, 1997
A commercial microalloyed steel was examined by optical and transmission electron microscopy in o... more A commercial microalloyed steel was examined by optical and transmission electron microscopy in order to determine the origin and the amount of carbonitride precipitation which had formed as the result of industrial processing on a hot strip mill. Almost one-half of the total microalloy addition (0'06Ti and 0'02Nb) had remained in the form of eutectic or undissolved particles after soaking. Intragranular nucleation of fine carbonitride particles was observed to have occurred only in austenite. No additional carbonitride particles had formed in ferrite during coiling and almost one-half of the microalloying elements dissolved during soaking had remained in solution at the end of the industrial rolling process. According to well established structure-property relationships, a precipitation strengthening potential of60-80 MN m-2 could be assigned to thecarbonitride particles which had nucleated in austenite. MSTj3416
Materials Research, 2011
Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density... more Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (%) respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 °C for 5 hours to decompose the carbonate and the second one at 1150 °C for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (%) of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%). The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide) was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (%) ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.
Transactions of Nonferrous Metals Society of China, 2022
Aluminum and their alloys are key materials for the automotive and aerospace industries. The disp... more Aluminum and their alloys are key materials for the automotive and aerospace industries. The dispersion of hard ceramic particles in the Al soft matrix produces lightweight composites with interesting properties, as environmental resistance, high specific strength and stiffness, high thermal and electrical conductivity, and good wear resistance, encouraging their technological use. Powder metallurgy techniques like mechanical alloying (MA) are very attractive to design metal matrix composites, as they are able to achieve a homogeneous distribution of well dispersed particles inside the metal matrix. In this work, pure aluminum has been reinforced with particles of Niobium carbide (NbC), an extremely hard and stable refractory ceramic. NbC is frequently used as a grain growth inhibitor in micro-alloyed steel due to their low solubility in austenite. In the present work, NbC is expected to act as a reinforcing phase by its fine dispersion into the aluminum matrix, produced by MA. Comp...
Journal of Alloys and Compounds, 2021
In this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under ... more In this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under both argon and hydrogen atmospheres. It is shown that this alloy forms a body-centered cubic (BCC) structure when milled under an argon atmosphere (mechanical alloying-MA) and a combination of BCC, FCC, and Mg2NiH4 when milled under hydrogen pressure (reactive milling-RM). The hydrogen storage behavior of the RM samples was evaluated by a combination of thermal analyses and manometric measurements in a Sieverts apparatus. The RM alloy presented a functional hydrogen storage capacity of 0.94 wt% and a very high hydrogen absorption and desorption kinetics at temperatures 100 °C lower than the one for the desorption temperature of the commercial MgH2. Electrochemical discharge of RM samples showed precisely the same hydrogen contend as that obtained in the gas desorption. Electrochemical charging/discharging experiments also were performed in the MA samples, which, however, presented lower electrochemical storage capacity, a behavior probably resulting from the instability of the alloy in the alkaline solution with the formation of a hydroxide layer on its surface that hinders the electrochemical reactions.
Surface and Coatings Technology, 2021
Abstract Laser materials processing is a very attractive technology, due not only to the vast num... more Abstract Laser materials processing is a very attractive technology, due not only to the vast number of applications in a wide range of materials and industrial segments but also due to the constant progress in the development of laser devices in terms of power, control, and costs. In metals processing technology, a high and precisely controlled density of energy concentrated in a small region imposes specific characteristics for the surface, keeping bulk properties unchanged. Alternatively, laser surface modification can result in outstanding surface properties to ordinary/low-cost metals. In the present work, the corrosion behavior of the Ti12Mo6Zr2Fe β-metastable alloy has been evaluated after laser surface melting and re-solidification under an inert atmosphere. It was found that this processing route produced significant metallurgical and chemistry changes on the surface of the alloy, including grain refinement and oxide formation. It resulted in a significant improvement in the corrosion properties in comparison to the passivated metal, as observed in potentiodynamic polarization curves and by electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). Electrical equivalent circuit (EEC) modeling of impedance data suggests that a duplex porous/dense passive layer present in the untreated alloy enables the occurrence of charge-transfer mechanisms at some extension while a thicker oxide layer present after laser texturing increases the capacitive behavior of the surface.
ABM Proceedings, 2014
High strength-light weight materials are very attractive for the transportation sector, particula... more High strength-light weight materials are very attractive for the transportation sector, particularly to the aerospace industry. High strength-age hardenable aluminium alloys are widely used in airframes due to their unique combination of strength, density, toughness, corrosion resistance, cost and easy processing. However, the hardening capacity of such alloys is somehow saturated due to thermodynamic issues related to the conventional processing. The production of aluminum-matrix composites is a promising strategy to overcome this limitation, resulting in strength levels that cannot be reached by actual commercial aluminum alloys. In the present work, multiwall carbon nanotubes were used to reinforce the AA6061 aluminium alloy. 1 and 2% weight percent of MWCNT were mixed to the alloy powder by highenergy ball-milling process. The blended powder was consolidated by hot extrusion. The obtained composite bars were submitted to heat treatment for the T6 condition in order to combine both CNT dispersion and precipitation hardening effects. Optical and scanning electron microscopy, as well as hardeness testing, was used to characterize the bars. Typical wrought microstructure, free of defects, was observed on the extruded bars. Hardness of the composites was observed to increase by 20, 28 and 68% for 1% MWCNT 6 h milling, 2% MWCNT 6 h milling and 2% MWCNT 10 h milling, respectively, in the as-extruded condition. The better performance for the composites blended at higher milling time was attributed to a better nanotubes dispersion. Subsequent heat treatment to the T6 condition did not result in additional hardening.
Key Engineering Materials, 2019
Coatings with high entropy alloys of the AlCoCrFeNiV system were obtained by selective laser melt... more Coatings with high entropy alloys of the AlCoCrFeNiV system were obtained by selective laser melting on low carbon steel substrates. The effect of the variation of the Fe and V contents as well as the laser processing parameters in the development of the coating were evaluated. The coatings were obtained from the simple powder mixtures of the high purity elemental components in a planetary ball mill. The coatings were obtained by using CO2 laser with a power of 100 W, diameter of 0.16 mm, and scan speed varying from 3 to 12 mm/s. Phase constituents, microstructure and hardness were investigated by XRD, SEM, and microhardness tester, respectively. Wear resistance measurements were carried out by the micro-abrasion method using ball-cratering tests. The coatings presented good adhesion to the substrate and high hardness, of the order of 480 to 650 HV. Most homogeneous coating with nominal composition was obtained by using the higher scan speed, 12 mm/s. Vanadium addition increased har...
Metallurgical and Materials Transactions B, 2017
Aluminum and its alloys are key materials for the transportation industry as they contribute to t... more Aluminum and its alloys are key materials for the transportation industry as they contribute to the development of lightweight structures. The dispersion of hard ceramic particles in the Al soft matrix can lead to a substantial strengthening effect, resulting in composite materials exhibiting interesting mechanical properties and inspiring their technological use in sectors like the automotive and aerospace industries. Powder metallurgy techniques are attractive to design metal matrix composites, achieving a homogeneous distribution of the reinforcement into the metal matrix. In this work, pure aluminum has been reinforced with particles of niobium carbide (NbC), an extremely hard and stable refractory ceramic. Its use as a reinforcing phase in metal matrix composites has not been deeply explored. Composite powders produced after different milling times, with 10 and 20 vol pct of NbC were produced by high-energy ball milling and characterized by scanning electron microscopy and by X-ray diffraction to establish a relationship between the milling time and size, morphology, and distribution of the particles in the composite powder. Subsequently, an Al/10 pct NbC composite powder was hot extruded into cylindrical bars. The strength of the obtained composite bars is comparable to the commercial high-strength, aeronautical-grade aluminum alloys.
Letters on Materials, 2018
Letters on Materials, 2018
Metals
In this study, we successfully obtained a 2Mg-Fe mixture through mechanical alloying (MA) and pro... more In this study, we successfully obtained a 2Mg-Fe mixture through mechanical alloying (MA) and processed it via accumulative roll bonding (ARB) (MA+ARB). Our primary focus was to analyze the impact of ambient air exposure while also evaluating the processing route. Some powder samples were exposed to air for 12 months (stored in a glass desiccator with an average yearly temperature and relative humidity of ~27 °C and 50.5%) before undergoing ARB processing. The Mg samples obtained after ARB processing exhibited a (002)-type texture. Our results demonstrate that all samples, including those processed via ARB, could rapidly absorb hydrogen within a matter of minutes despite considerable differences in surface area between powders and rolled samples. Grain size reduction by MA and ARB processing and texturing may have influenced this behavior. ARB-processed samples reached approximately 60% (~1.8 wt.%) of their maximum acquired capacity within just 24 min compared to powders (~2.2 wt.%)...
Journal of Materials Research, 2020
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Materials Science Forum, 2000
Many high-strength Al-based alloys have been developed recently after it was found that for certa... more Many high-strength Al-based alloys have been developed recently after it was found that for certain composition range, crystallisation from amorphous alloys could lead to a composite structure consisting of primary nanocrystals embedded in an amorphous matrix. However, even better values of mechanical strength,vas reported for Al-bused fully crystallised alloys with a composite structure formed by a mixture of primary nanocrystals and quasicrystalline phases therefore, the development of new compositions continues to be of interest. In the present work we report on the crystallisation behaviour of amorphous melt-spun Al-Fc-Nd-Cu alloys. Crystallisation was studied by differential scanning calorimetry and the characterisation of samples partially and fully crystallised was performed by X-ray diffraction and transmission electron microscopy. For the alloy Al85Fe4Nd6Cu5 crystallisation occurred by multiple stage with the first peak being associated with primary Al and two DSC peaks observed at higher temperatures have been associated with metastable phases. These results are discussed in association with the effect of the Cu content ill the crystallisation behaviour as compared with Al-Fe-Nd alloys.Univ Fed Sao Paulo, Dept Mat Engn, BR-13565905 Sao Carlos, SP, BrazilInst Natl Polytech Grenoble, CNRS, LTPCM, FR-38402 St Martin Dheres, FranceUniv Fed Sao Paulo, Dept Mat Engn, BR-13565905 Sao Carlos, SP, BrazilWeb of Scienc
Materials Science Forum, 2014
The AISI 52100 steel is a material widely used in the industry due to its high fatigue resistance... more The AISI 52100 steel is a material widely used in the industry due to its high fatigue resistance, dimensional stability, high hardness and wear resistance. This steel is used for production of ball bearings, stamping tools, etc. In case of production of ball bearings and its track this material is spherodized because, due to its high content of carbon, about 1%, it has high mechanical strength making it impossible to cold forming. To obtain a wear resistant surface, after forming, this material is hardened and tempered. Normally to obtain the AISI 52100 steel, arc electric melting furnace is used. This work aims the reuse of AISI 52100 steel by powder metallurgy route, starting from the machined chips using high energy mill (planetary) to obtain the powder. Then, the powder was uniaxially pressed into a press with a load of 4 tons, to form the specimen, later on pressed in an isostatic press at a pressure of 300MPa to obtain a better densification. To analyze the powder morphology ...
METALLIC …, 2005
After 80 h of milling the elemental powders, mechanical alloying of Al 90 Fe 5 Nd 5 produces a na... more After 80 h of milling the elemental powders, mechanical alloying of Al 90 Fe 5 Nd 5 produces a nanostructured composite, which consists of nanocrystals of fcc-Al and some Al 11 Nd 3 precipitates, embedded in an amorphous matrix. This composite has a Vickers hardness ...
ABM Proceedings, 2014
Resumo O aço inoxidável austenítico 316 (316 SS) é um dos materiais metálicos mais utilizados em ... more Resumo O aço inoxidável austenítico 316 (316 SS) é um dos materiais metálicos mais utilizados em aplicações médicas devido à combinação de propriedades mecânicas e do baixo custo. No entanto, desgaste e corrosão estimulam mudanças permanentes no tecido humano que podem levar à perda do implante. O desenvolvimento de recobrimentos biocompatíveis e estáveis, que apresentem propriedades mecânicas adequadas, e que não sofram ruptura ou delaminação durante o uso, é uma solução muito promissora para melhorar o desempenho do 316 SS como biomaterial para implantes. Neste trabalho, uma liga intermetálica FeAlCr, que tem apresentado propriedades adequadas para a aplicação como biomaterial, foi utilizada como recobrimento sobre um aço inoxidável 316 de grau médico. O revestimento foi obtido utilizando-se a técnica magnetron sputtering por corrente contínua. Os parâmetros de deposição, como distância substrato-alvo e pressão de gás argônio foram mantidos fixos em 50 mm e 5 mTorr, respectivamente. As amostras foram preparadas com os seguintes valores de potência de sputtering: 50 W, 75W, 100 W e 150 W. A adesão dos filmes foi analisada por teste de scratch, enquanto a espessura e a taxa de deposição foram analisadas por perfilometria ótica. As características estruturais foram analisadas por microscopia eletrônica de varredura com EDS. Palavras-chave: Sputtering; Aço inoxidável; Liga FeAlCr; Biomaterial DEPOSITION OF THIN FILMS OF INTERMETALLIC FeAlCr ALLOY BY SPUTTERING FOR BIOMATERIALS APPLICATION Abstract The 316 type austenitic stainless steel (316 SS) is one of the most used metallic materials in medical applications due to the combination of mechanical properties with low cost. However, wear and corrosion behavior stimulate permanent changes in human tissue that can lead to implant loss. The development of stable and biocompatible coatings presenting suitable mechanical properties and which does not undergo cracking or to peel off during the use is a very promising solution for improving the performance of 316 SS as biomaterials for implants. In this paper a coating based on an intermetallic FeAlCr alloy, material that have been presenting suitable properties for biomaterial application, was deposited on a 316 medical grade stainless steel. The coating was obtained by using a direct-current magnetron sputtering. During deposition the parameters substrate-target distance and argon gas pressure were fixed at 50mm and 5 mTorr, respectively. Samples were produced using the following sputtering power: 50 W, 75W, 100 W and 150 W. The films obtained were examined for adhesion to the substrate through the scratch test, while the thickness and deposition rate was analyzed by profilometry. Structural characteristics were evaluated by scanning electron microscopy with EDS
Materials Science and Technology, 1997
A commercial microalloyed steel was examined by optical and transmission electron microscopy in o... more A commercial microalloyed steel was examined by optical and transmission electron microscopy in order to determine the origin and the amount of carbonitride precipitation which had formed as the result of industrial processing on a hot strip mill. Almost one-half of the total microalloy addition (0'06Ti and 0'02Nb) had remained in the form of eutectic or undissolved particles after soaking. Intragranular nucleation of fine carbonitride particles was observed to have occurred only in austenite. No additional carbonitride particles had formed in ferrite during coiling and almost one-half of the microalloying elements dissolved during soaking had remained in solution at the end of the industrial rolling process. According to well established structure-property relationships, a precipitation strengthening potential of60-80 MN m-2 could be assigned to thecarbonitride particles which had nucleated in austenite. MSTj3416
Materials Research, 2011
Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density... more Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (%) respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 °C for 5 hours to decompose the carbonate and the second one at 1150 °C for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (%) of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%). The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide) was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (%) ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.
Transactions of Nonferrous Metals Society of China, 2022
Aluminum and their alloys are key materials for the automotive and aerospace industries. The disp... more Aluminum and their alloys are key materials for the automotive and aerospace industries. The dispersion of hard ceramic particles in the Al soft matrix produces lightweight composites with interesting properties, as environmental resistance, high specific strength and stiffness, high thermal and electrical conductivity, and good wear resistance, encouraging their technological use. Powder metallurgy techniques like mechanical alloying (MA) are very attractive to design metal matrix composites, as they are able to achieve a homogeneous distribution of well dispersed particles inside the metal matrix. In this work, pure aluminum has been reinforced with particles of Niobium carbide (NbC), an extremely hard and stable refractory ceramic. NbC is frequently used as a grain growth inhibitor in micro-alloyed steel due to their low solubility in austenite. In the present work, NbC is expected to act as a reinforcing phase by its fine dispersion into the aluminum matrix, produced by MA. Comp...
Journal of Alloys and Compounds, 2021
In this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under ... more In this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under both argon and hydrogen atmospheres. It is shown that this alloy forms a body-centered cubic (BCC) structure when milled under an argon atmosphere (mechanical alloying-MA) and a combination of BCC, FCC, and Mg2NiH4 when milled under hydrogen pressure (reactive milling-RM). The hydrogen storage behavior of the RM samples was evaluated by a combination of thermal analyses and manometric measurements in a Sieverts apparatus. The RM alloy presented a functional hydrogen storage capacity of 0.94 wt% and a very high hydrogen absorption and desorption kinetics at temperatures 100 °C lower than the one for the desorption temperature of the commercial MgH2. Electrochemical discharge of RM samples showed precisely the same hydrogen contend as that obtained in the gas desorption. Electrochemical charging/discharging experiments also were performed in the MA samples, which, however, presented lower electrochemical storage capacity, a behavior probably resulting from the instability of the alloy in the alkaline solution with the formation of a hydroxide layer on its surface that hinders the electrochemical reactions.
Surface and Coatings Technology, 2021
Abstract Laser materials processing is a very attractive technology, due not only to the vast num... more Abstract Laser materials processing is a very attractive technology, due not only to the vast number of applications in a wide range of materials and industrial segments but also due to the constant progress in the development of laser devices in terms of power, control, and costs. In metals processing technology, a high and precisely controlled density of energy concentrated in a small region imposes specific characteristics for the surface, keeping bulk properties unchanged. Alternatively, laser surface modification can result in outstanding surface properties to ordinary/low-cost metals. In the present work, the corrosion behavior of the Ti12Mo6Zr2Fe β-metastable alloy has been evaluated after laser surface melting and re-solidification under an inert atmosphere. It was found that this processing route produced significant metallurgical and chemistry changes on the surface of the alloy, including grain refinement and oxide formation. It resulted in a significant improvement in the corrosion properties in comparison to the passivated metal, as observed in potentiodynamic polarization curves and by electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). Electrical equivalent circuit (EEC) modeling of impedance data suggests that a duplex porous/dense passive layer present in the untreated alloy enables the occurrence of charge-transfer mechanisms at some extension while a thicker oxide layer present after laser texturing increases the capacitive behavior of the surface.
ABM Proceedings, 2014
High strength-light weight materials are very attractive for the transportation sector, particula... more High strength-light weight materials are very attractive for the transportation sector, particularly to the aerospace industry. High strength-age hardenable aluminium alloys are widely used in airframes due to their unique combination of strength, density, toughness, corrosion resistance, cost and easy processing. However, the hardening capacity of such alloys is somehow saturated due to thermodynamic issues related to the conventional processing. The production of aluminum-matrix composites is a promising strategy to overcome this limitation, resulting in strength levels that cannot be reached by actual commercial aluminum alloys. In the present work, multiwall carbon nanotubes were used to reinforce the AA6061 aluminium alloy. 1 and 2% weight percent of MWCNT were mixed to the alloy powder by highenergy ball-milling process. The blended powder was consolidated by hot extrusion. The obtained composite bars were submitted to heat treatment for the T6 condition in order to combine both CNT dispersion and precipitation hardening effects. Optical and scanning electron microscopy, as well as hardeness testing, was used to characterize the bars. Typical wrought microstructure, free of defects, was observed on the extruded bars. Hardness of the composites was observed to increase by 20, 28 and 68% for 1% MWCNT 6 h milling, 2% MWCNT 6 h milling and 2% MWCNT 10 h milling, respectively, in the as-extruded condition. The better performance for the composites blended at higher milling time was attributed to a better nanotubes dispersion. Subsequent heat treatment to the T6 condition did not result in additional hardening.
Key Engineering Materials, 2019
Coatings with high entropy alloys of the AlCoCrFeNiV system were obtained by selective laser melt... more Coatings with high entropy alloys of the AlCoCrFeNiV system were obtained by selective laser melting on low carbon steel substrates. The effect of the variation of the Fe and V contents as well as the laser processing parameters in the development of the coating were evaluated. The coatings were obtained from the simple powder mixtures of the high purity elemental components in a planetary ball mill. The coatings were obtained by using CO2 laser with a power of 100 W, diameter of 0.16 mm, and scan speed varying from 3 to 12 mm/s. Phase constituents, microstructure and hardness were investigated by XRD, SEM, and microhardness tester, respectively. Wear resistance measurements were carried out by the micro-abrasion method using ball-cratering tests. The coatings presented good adhesion to the substrate and high hardness, of the order of 480 to 650 HV. Most homogeneous coating with nominal composition was obtained by using the higher scan speed, 12 mm/s. Vanadium addition increased har...
Metallurgical and Materials Transactions B, 2017
Aluminum and its alloys are key materials for the transportation industry as they contribute to t... more Aluminum and its alloys are key materials for the transportation industry as they contribute to the development of lightweight structures. The dispersion of hard ceramic particles in the Al soft matrix can lead to a substantial strengthening effect, resulting in composite materials exhibiting interesting mechanical properties and inspiring their technological use in sectors like the automotive and aerospace industries. Powder metallurgy techniques are attractive to design metal matrix composites, achieving a homogeneous distribution of the reinforcement into the metal matrix. In this work, pure aluminum has been reinforced with particles of niobium carbide (NbC), an extremely hard and stable refractory ceramic. Its use as a reinforcing phase in metal matrix composites has not been deeply explored. Composite powders produced after different milling times, with 10 and 20 vol pct of NbC were produced by high-energy ball milling and characterized by scanning electron microscopy and by X-ray diffraction to establish a relationship between the milling time and size, morphology, and distribution of the particles in the composite powder. Subsequently, an Al/10 pct NbC composite powder was hot extruded into cylindrical bars. The strength of the obtained composite bars is comparable to the commercial high-strength, aeronautical-grade aluminum alloys.