Funds were provided by Spanish Government (programme MINECO, ref. MAT2012-38650-C02-01), Regional... more Funds were provided by Spanish Government (programme MINECO, ref. MAT2012-38650-C02-01), Regional Government of Madrid (programme MULTIMAT-CHALLENGE, ref. S2013/MIT-2862) and Institute of Alvaro Alonso Barba (IAAB) for the research stay in CMEMS-UMINHO (University of Minho).
En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-... more En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composición utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusión por arco tres aleaciones con contenidos que varían entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendrítica bifásica similar, siendo las dendritas una solución sólida bcc enriquecida en Ti, V o Cr. El escandio aparece únicamente en el espacio interdendrítico formando el intermetálico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Además, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo ésta mayor cuanto más blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empíricos utilizados ni los cálculos mediante THERMOCALC permiten predecir la formación de una única soluc...
Journal of the Mechanical Behavior of Biomedical Materials, 2018
Dry sliding wear behaviour of β-type Ti-Nb and Ti-Mo surfaces designed by diffusion treatments fo... more Dry sliding wear behaviour of β-type Ti-Nb and Ti-Mo surfaces designed by diffusion treatments for biomedical applications.
The cellular behaviour of bone marrow stromal cells on titanium surfaces modified by niobium diff... more The cellular behaviour of bone marrow stromal cells on titanium surfaces modified by niobium diffusion is presented in order to test their osteogenic differentiation response after culturing for 21 days. The surface modification of Ti substrates produced by powder metallurgy was performed through niobium diffusion treatments. Ti-Nb exhibited a β-Ti surface together with a microstructural (β / α+β / α) and compositional (Ti-Nb) gradient which enhances hardness, wear resistance and lowers the elastic modulus making it more similar to the human bone. Furthermore, the Ti-NbNH4Cl by means of the activating agent achieved three times the hardness of Ti together with a porous surface. The in vitro osteogenic differentiation response of bone marrow stromal cells on both Ti-Nb surfaces indicated the positive cell-material interaction. The osteogenic differentiation of cells was successful after 21 days, considering the positive response in terms of increased cell viability, lactate dehydrogenase-(LDH) activity, alkaline phosphatase-(ALP) activity expression (osteogenic marker) and bone-like nodules deposition by ST-2 cells as a bone mineralization cue. Therefore, the positive effect of a low elastic modulus Ti-Nb surface and a porous nitride Ti-NbNH4Cl with suitable wettability and average roughness values on the osteogenic differentiation response of bone marrow stromal cells is demonstrated.
This work focuses on the bioactivity and biological response of modified Ti surfaces produced by ... more This work focuses on the bioactivity and biological response of modified Ti surfaces produced by powder metallurgy. They are processed by diffusion of two β-stabilizing elements, Nb and Mo, deposited onto the surface of PM Ti substrates. Moreover, the addition of an activating agent, NH 4 Cl, to the suspension has been carried out by thermo-reactive diffusion process. The surface modification led to a gradient in composition (Ti-Nb or Ti-Mo) and microstructure (β -α+β -α phases). This work presents the bioactivity results of these Ti-Mo and Ti-Nb surfaces as well as the cellmaterial response of the Ti-Nb surfaces. The reactivity of the materials was tested through immersion in simulated body fluid considering Ca and P precipitation in order to assess the ability of the materials to induce hydroxyapatite formation. The in-vitro cell response was evaluated by human osteoblast-like cells incubation on the different surfaces for 48 hours. The investigation led to positive results in terms of surface bioactivity and an improved cell-material interaction of the PM modified Ti-Nb surfaces compared to the reference Ti material.
Corrosion and tribocorrosion behaviour of modified Ti surfaces through thermochemical treatments ... more Corrosion and tribocorrosion behaviour of modified Ti surfaces through thermochemical treatments has been studied. Electrochemical Impedance Spectroscopy (EIS) and reciprocating sliding tests using a ball-on-plate tribometer under 1 N load and alumina as counter-material were used to evaluate the influence of Nb and Mo on titanium corrosion and tribocorrosion properties. Ti-Nb and Ti-Mo surfaces exhibited better anticorrosive properties than CP-titanium. Under tribological action the modified Ti surfaces showed similar coefficient of friction and lower tendency to corrosion compared to CP-Ti. Furthermore, Nb diffusion increased the repassivation rate with respect to Ti and Ti-Mo surfaces due to its stable passive film.
Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced... more Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced, and this can be effectively accomplished by surface treatment. Molybdenizing is a surface treatment where molybdenum is introduced into the surface of titanium alloys causing the formation of wear-resistant surface layers containing molybdenum, while aluminizing of titanium-based alloys has been reported to improve their high temperature oxidation properties. Whereas pack cementation and other surface modification methods have been used for molybdenizing or aluminizing of wrought and/or cast pure titanium and titanium alloys, such surface treatments have not been reported on titanium alloys produced by powder metallurgy (PM). Also a critical understanding of the process parameters for simultaneous one step molybdeno-aluminizing of titanium alloys by pack cementation and the predominant mechanism for this process have not been reported. The current research work describes the surface modification of titanium and Ti-6Al-4V prepared by PM by molybdeno-aluminizing and analyzes thermodynamic aspects of the deposition process. Similar coatings are also deposited to wrought Ti-6Al-4V and compared. Characterization of the coatings was carried out using scanning electron microscopy and x-ray diffraction. For both titanium and Ti-6Al-4V, the use of a powder pack containing ammonium chloride as activator leads to the deposition of molybdenum and aluminium into the surface but also introduces nitrogen causing the formation of a thin titanium nitride layer. In addition, various titanium aluminides and mixed titanium aluminium nitrides are formed. The appropriate conditions for molybdeno-aluminizing as well as the phases expected to be formed were successfully determined by thermodynamic equilibrium calculations.
This contribution focuses on modifying the composition and surface characteristics of powder meta... more This contribution focuses on modifying the composition and surface characteristics of powder metallurgy titanium substrates to improve their wear resistance and to reduce the surface Young´s modulus, while maintaining the corrosion resistance and biocompatibility. The modification consists of Mo and TiN coatings produced by colloidal techniques which are deposited by electrophoretic deposition (EPD) or spraying onto green or sintered titanium substrates. The final surface structures are formed during a heat treatment, during which diffusion and consolidation of the layers take place. The surfaces are characterised by XRD, SEM, and micro-indentation; showing diffusion areas of between 40 and 85 microns with clear microstructural changes as well as higher hardness values.
International Journal of Refractory Metals and Hard Materials, 2015
The aim of this work is the design, processing and characterization of a metal-ceramic composite ... more The aim of this work is the design, processing and characterization of a metal-ceramic composite (cermet) with an iron -aluminum alloy as metallic matrix and NbC as ceramic phase. The cermet is obtained from a composite powder containing in situ formed NbCrich precipitates on an iron rich metal matrix. The starting powder was supplied by CBMM (Brazil), and it was produced by a synthesis process under development which introduces other metals such as Al, Si and Ti to the composition. Due to the in situ process, good bonding is expected between the carbide and the matrix. However it is necessary to study the processability of those complex particles and the transformations occurring during sintering to get the final microstructure. Thermodynamic studies by means of ThermoCalc ® software were performed to predict the phases stable with the starting composition and also the influence of Fe and C additions. Samples were produced by uniaxial pressing and vacuum sintering (PS), and also by Field Assisted Hot Pressing (FAHP). The processing parameters for PS processing, that is, sintering temperature and time were based on themodynamic simulations by ThermoCalc ® software together with thermal analysis. The powders were characterized by measuring density, particle size, carbon content and chemical composition; and consolidated samples by density and Vickers hardness. The microstructure and morphology of the powder and consolidated samples was analyzed by SEM. The addition of Fe and both C and Fe to the starting cermet composition provided good results as the final microstructure consisted essentially of NbC and Fe matrix.
Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is throug... more Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is through surface treatment. Boronizing is a surface treatment in which boron diffuses into the surface of Ti leading to the formation of hard and wear-resistant Ti borides. Boronizing of wrought and/or cast Ti alloys by pack cementation has been studied, while similar coatings
In this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic co... more In this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic components are examined. The deposition was accomplished with pack cementation chemical deposition. The examination of the samples was performed with electron microscopy and X-ray diffraction analysis. It was found that coatings on Cu substrate consist of two layers with different Zn concentrations, while coatings on brass were single layered with almost constant Zn concentration. The presence of distinct Zn-Cu phases was revealed in both cases. The subjection of the as coated samples together with the uncoated substrates in air at 400ºC showed that both Zn coated samples have enhanced resistivity in such atmospheres, as most of the coating remained mostly unoxidised, and the substrates were fully protected. On the contrary, the bare substrates appear to have undergone severe damage as brittle oxides were formed on their surface.
Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag... more Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag2O films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2:3 by changing substrate temperature (Ts). Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag2O films deposited at values of Ts below 200 °C are (111) preferentially oriented, which may be due to the smallest free energy of the (111) crystalline face. The film crystallization becomes poor as the value of Ts increases from 100 °C to 225 °C. In particular, the Ag2O film deposited at Ts = 225 °C loses the 〈111〉 preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films.
A novel slurry-based process for aluminizing nickel foams while improving the mechanical properti... more A novel slurry-based process for aluminizing nickel foams while improving the mechanical properties and conserving the excellent ductility is reported. Cellular unalloyed nickel foams with 92% porosity and uniform pore size and distribution were used as a starting material. Several slurries of different compositions were examined to investigate the possibility of developing an aluminide-nickel intermetallic coating on a Ni foam
Índice ___________________________________________________________ 4 Índice de tablas ___________... more Índice ___________________________________________________________ 4 Índice de tablas ____________________________________________________ 5 Índice de figuras ___________________________________________________ 6 Cap 1 Objetivos y fases de desarrollo__________________________________ 9 Cap 2 Introducción________________________________________________ 10 2.1 Aspectos básicos del titanio y sus aleaciones 2.1.1 Propiedades fundamentales del titanio 2.1.2 Procesos de obtención del titanio 2.1.3 Aleaciones de titanio 2.1.4 Propiedades de las aleaciones del titanio 2.1.5 Propiedades de la aleación Ti-64 2.1.6 Oxidación del titanio. 2.1.7 Aleante Molibdeno 2.1.8 Aleante Niobio 2.2 Tratamientos superficiales 2.3 Proceso de difusión 2.4 Funcionamiento del activador Cap 3 Procedimiento experimental___________________________________ 25 3.1 Materiales empleados 3.2 Preparación de las muestras de Ti 3.3 Preparación del slurry para la difusión 3.4 Difusión sobre el titanio 3.5 Análisis por difracción de rayos X (DRX) 3.6 Recubrimiento de cobre 3.7 Embutición de las piezas 3.8 Análisis de microscopia electrónica de barrido (SEM) 3.9 Software de simulación DICTRA TERMOCALC Cap 4 Resultados__________________________________________________32 4.1 Cálculos previos al experimento utilizando las leyes de Fick. 4.2 Simulación numérica de los experimentos utilizando DICTRA TERMOCALC software 4.3 Resultados experimentales 4.3.1 Resultados de los experimentos realizados a 1100ºC 4.3.2 Resultados de los experimentos realizados a 750º Cap 5 Conclusiones y futuras líneas de investigación______________________67 5.1 Conclusiones 5.2 Futuras líneas de investigación Cap 6 Referencias_________________________________________________ 69
Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of mo... more Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of modified PM Ti surfaces designed for biomedical applications, Powder Metallurgy, 61(2), pp. 90-99.
Boletín de la Sociedad Española de Cerámica y Vidrio
Abstract MAX phases exhibit excellent combination of ceramic and metallic-like properties. In thi... more Abstract MAX phases exhibit excellent combination of ceramic and metallic-like properties. In this work, MAX phase Ti3SiC2 powder was synthesized starting-off with different combinations of elemental powders and carbides. The powders used were Ti, Si, C, SiC and TiC in different combinations, molar ratios and powder size. Powders were heat treated on a vacuum furnace for different times and temperatures for in situ production of the Ti3SiC2 MAX phase. High purity synthesized samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to identify and quantify the different phase constituents present. The main phase constituents in the powders produced were Ti3SiC2 and TiSi2. Up to 94% of Ti3SiC2 MAX phase was obtained using Ti:SiC:C as starting powders in a molar ratio of 3:1.5:0.5. Different phase constitution was observed on the surface and the centre of the samples. An optimal starting powder composition, molar ratio, heat treatment temperature and time is proposed for the formation of high purity Ti3SiC2 MAX phase. Selected mixture was studied thermodynamically and a reaction mechanism of formation of the MAX phase is proposed.
Abstract MAX phase foams could have various applications where tailored functional and mechanical... more Abstract MAX phase foams could have various applications where tailored functional and mechanical properties are required. In this study, Ti2AlC and Ti3SiC2 MAX phase foams with controlled porosity and pore size were produced and characterized. The foams were produced from MAX phase powders by powder metallurgy method using crystalline carbohydrate as a space holder. Foams with overall porosity up to approximately 71 vol% and pore size from 250 μm to 1000 μm were successfully produced; micro-porosity and macro-porosity was characterized. Poisson's ratio and elastic moduli of the foams were measured by resonant ultrasound spectroscopy (RUS) and analyzed as a function of porosity and pore size. Different models were used to fit the experimental data and interpret the effect of pore size and amount of porosity and on elastic properties. It was found that the amount and type of porosity has a larger influence on the elastic properties than the pore size.
MAX phase foams from commercial Ti 2 AlC powder were prepared by a novel powder processing method... more MAX phase foams from commercial Ti 2 AlC powder were prepared by a novel powder processing method using raw sugar as space-holder. Manufacturing MAX phase foams using this method involves mixing Ti 2 AlC powder with raw sugar, pressing the mixture to form a green body followed by space-holder removal and sintering. Green bodies were formed using cold uniaxial pressing and porosity was controlled varying the size and amount of the raw sugar space-holder. Three different space-holder particles sizes in the range of 250-1000 µm and four different volume amounts (20%, 40%, 60% and 80%) of space-holder were studied. The foams produced were characterized, and the size distribution and amount of resulting porosity was compared with the theoretically expected values. Optimal conditions using this novel processing technique for this material were established aiming towards controlling the final microstructures and properties, of porous Ti 2 AlC MAX phase.
Abstract Magnesium disilicide is a narrow gap semiconductor which can be used in several applicat... more Abstract Magnesium disilicide is a narrow gap semiconductor which can be used in several applications such as thermoelectric materials, optoelectronic devices and batteries. It has attracted special attraction because of its low cost and non-toxicity. In the herein examination the formation of this compound is investigated by a simple, one-stage process which is pack cementation. Particularly, the effect of deposition time, activator and donor material concentration was examined. Mg2Si was formed in every case without the presence of other compounds as referred to be present when formed with other coating procedures which have higher cost and are very sophisticated. The examined parameters were found to have effect only on the coating thickness up to a certain value. Moreover, the experimental results confirmed the theoretical thermodynamic calculations performed for this case.
Funds were provided by Spanish Government (programme MINECO, ref. MAT2012-38650-C02-01), Regional... more Funds were provided by Spanish Government (programme MINECO, ref. MAT2012-38650-C02-01), Regional Government of Madrid (programme MULTIMAT-CHALLENGE, ref. S2013/MIT-2862) and Institute of Alvaro Alonso Barba (IAAB) for the research stay in CMEMS-UMINHO (University of Minho).
En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-... more En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composición utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusión por arco tres aleaciones con contenidos que varían entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendrítica bifásica similar, siendo las dendritas una solución sólida bcc enriquecida en Ti, V o Cr. El escandio aparece únicamente en el espacio interdendrítico formando el intermetálico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Además, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo ésta mayor cuanto más blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empíricos utilizados ni los cálculos mediante THERMOCALC permiten predecir la formación de una única soluc...
Journal of the Mechanical Behavior of Biomedical Materials, 2018
Dry sliding wear behaviour of β-type Ti-Nb and Ti-Mo surfaces designed by diffusion treatments fo... more Dry sliding wear behaviour of β-type Ti-Nb and Ti-Mo surfaces designed by diffusion treatments for biomedical applications.
The cellular behaviour of bone marrow stromal cells on titanium surfaces modified by niobium diff... more The cellular behaviour of bone marrow stromal cells on titanium surfaces modified by niobium diffusion is presented in order to test their osteogenic differentiation response after culturing for 21 days. The surface modification of Ti substrates produced by powder metallurgy was performed through niobium diffusion treatments. Ti-Nb exhibited a β-Ti surface together with a microstructural (β / α+β / α) and compositional (Ti-Nb) gradient which enhances hardness, wear resistance and lowers the elastic modulus making it more similar to the human bone. Furthermore, the Ti-NbNH4Cl by means of the activating agent achieved three times the hardness of Ti together with a porous surface. The in vitro osteogenic differentiation response of bone marrow stromal cells on both Ti-Nb surfaces indicated the positive cell-material interaction. The osteogenic differentiation of cells was successful after 21 days, considering the positive response in terms of increased cell viability, lactate dehydrogenase-(LDH) activity, alkaline phosphatase-(ALP) activity expression (osteogenic marker) and bone-like nodules deposition by ST-2 cells as a bone mineralization cue. Therefore, the positive effect of a low elastic modulus Ti-Nb surface and a porous nitride Ti-NbNH4Cl with suitable wettability and average roughness values on the osteogenic differentiation response of bone marrow stromal cells is demonstrated.
This work focuses on the bioactivity and biological response of modified Ti surfaces produced by ... more This work focuses on the bioactivity and biological response of modified Ti surfaces produced by powder metallurgy. They are processed by diffusion of two β-stabilizing elements, Nb and Mo, deposited onto the surface of PM Ti substrates. Moreover, the addition of an activating agent, NH 4 Cl, to the suspension has been carried out by thermo-reactive diffusion process. The surface modification led to a gradient in composition (Ti-Nb or Ti-Mo) and microstructure (β -α+β -α phases). This work presents the bioactivity results of these Ti-Mo and Ti-Nb surfaces as well as the cellmaterial response of the Ti-Nb surfaces. The reactivity of the materials was tested through immersion in simulated body fluid considering Ca and P precipitation in order to assess the ability of the materials to induce hydroxyapatite formation. The in-vitro cell response was evaluated by human osteoblast-like cells incubation on the different surfaces for 48 hours. The investigation led to positive results in terms of surface bioactivity and an improved cell-material interaction of the PM modified Ti-Nb surfaces compared to the reference Ti material.
Corrosion and tribocorrosion behaviour of modified Ti surfaces through thermochemical treatments ... more Corrosion and tribocorrosion behaviour of modified Ti surfaces through thermochemical treatments has been studied. Electrochemical Impedance Spectroscopy (EIS) and reciprocating sliding tests using a ball-on-plate tribometer under 1 N load and alumina as counter-material were used to evaluate the influence of Nb and Mo on titanium corrosion and tribocorrosion properties. Ti-Nb and Ti-Mo surfaces exhibited better anticorrosive properties than CP-titanium. Under tribological action the modified Ti surfaces showed similar coefficient of friction and lower tendency to corrosion compared to CP-Ti. Furthermore, Nb diffusion increased the repassivation rate with respect to Ti and Ti-Mo surfaces due to its stable passive film.
Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced... more Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced, and this can be effectively accomplished by surface treatment. Molybdenizing is a surface treatment where molybdenum is introduced into the surface of titanium alloys causing the formation of wear-resistant surface layers containing molybdenum, while aluminizing of titanium-based alloys has been reported to improve their high temperature oxidation properties. Whereas pack cementation and other surface modification methods have been used for molybdenizing or aluminizing of wrought and/or cast pure titanium and titanium alloys, such surface treatments have not been reported on titanium alloys produced by powder metallurgy (PM). Also a critical understanding of the process parameters for simultaneous one step molybdeno-aluminizing of titanium alloys by pack cementation and the predominant mechanism for this process have not been reported. The current research work describes the surface modification of titanium and Ti-6Al-4V prepared by PM by molybdeno-aluminizing and analyzes thermodynamic aspects of the deposition process. Similar coatings are also deposited to wrought Ti-6Al-4V and compared. Characterization of the coatings was carried out using scanning electron microscopy and x-ray diffraction. For both titanium and Ti-6Al-4V, the use of a powder pack containing ammonium chloride as activator leads to the deposition of molybdenum and aluminium into the surface but also introduces nitrogen causing the formation of a thin titanium nitride layer. In addition, various titanium aluminides and mixed titanium aluminium nitrides are formed. The appropriate conditions for molybdeno-aluminizing as well as the phases expected to be formed were successfully determined by thermodynamic equilibrium calculations.
This contribution focuses on modifying the composition and surface characteristics of powder meta... more This contribution focuses on modifying the composition and surface characteristics of powder metallurgy titanium substrates to improve their wear resistance and to reduce the surface Young´s modulus, while maintaining the corrosion resistance and biocompatibility. The modification consists of Mo and TiN coatings produced by colloidal techniques which are deposited by electrophoretic deposition (EPD) or spraying onto green or sintered titanium substrates. The final surface structures are formed during a heat treatment, during which diffusion and consolidation of the layers take place. The surfaces are characterised by XRD, SEM, and micro-indentation; showing diffusion areas of between 40 and 85 microns with clear microstructural changes as well as higher hardness values.
International Journal of Refractory Metals and Hard Materials, 2015
The aim of this work is the design, processing and characterization of a metal-ceramic composite ... more The aim of this work is the design, processing and characterization of a metal-ceramic composite (cermet) with an iron -aluminum alloy as metallic matrix and NbC as ceramic phase. The cermet is obtained from a composite powder containing in situ formed NbCrich precipitates on an iron rich metal matrix. The starting powder was supplied by CBMM (Brazil), and it was produced by a synthesis process under development which introduces other metals such as Al, Si and Ti to the composition. Due to the in situ process, good bonding is expected between the carbide and the matrix. However it is necessary to study the processability of those complex particles and the transformations occurring during sintering to get the final microstructure. Thermodynamic studies by means of ThermoCalc ® software were performed to predict the phases stable with the starting composition and also the influence of Fe and C additions. Samples were produced by uniaxial pressing and vacuum sintering (PS), and also by Field Assisted Hot Pressing (FAHP). The processing parameters for PS processing, that is, sintering temperature and time were based on themodynamic simulations by ThermoCalc ® software together with thermal analysis. The powders were characterized by measuring density, particle size, carbon content and chemical composition; and consolidated samples by density and Vickers hardness. The microstructure and morphology of the powder and consolidated samples was analyzed by SEM. The addition of Fe and both C and Fe to the starting cermet composition provided good results as the final microstructure consisted essentially of NbC and Fe matrix.
Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is throug... more Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is through surface treatment. Boronizing is a surface treatment in which boron diffuses into the surface of Ti leading to the formation of hard and wear-resistant Ti borides. Boronizing of wrought and/or cast Ti alloys by pack cementation has been studied, while similar coatings
In this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic co... more In this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic components are examined. The deposition was accomplished with pack cementation chemical deposition. The examination of the samples was performed with electron microscopy and X-ray diffraction analysis. It was found that coatings on Cu substrate consist of two layers with different Zn concentrations, while coatings on brass were single layered with almost constant Zn concentration. The presence of distinct Zn-Cu phases was revealed in both cases. The subjection of the as coated samples together with the uncoated substrates in air at 400ºC showed that both Zn coated samples have enhanced resistivity in such atmospheres, as most of the coating remained mostly unoxidised, and the substrates were fully protected. On the contrary, the bare substrates appear to have undergone severe damage as brittle oxides were formed on their surface.
Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag... more Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag2O films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2:3 by changing substrate temperature (Ts). Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag2O films deposited at values of Ts below 200 °C are (111) preferentially oriented, which may be due to the smallest free energy of the (111) crystalline face. The film crystallization becomes poor as the value of Ts increases from 100 °C to 225 °C. In particular, the Ag2O film deposited at Ts = 225 °C loses the 〈111〉 preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films.
A novel slurry-based process for aluminizing nickel foams while improving the mechanical properti... more A novel slurry-based process for aluminizing nickel foams while improving the mechanical properties and conserving the excellent ductility is reported. Cellular unalloyed nickel foams with 92% porosity and uniform pore size and distribution were used as a starting material. Several slurries of different compositions were examined to investigate the possibility of developing an aluminide-nickel intermetallic coating on a Ni foam
Índice ___________________________________________________________ 4 Índice de tablas ___________... more Índice ___________________________________________________________ 4 Índice de tablas ____________________________________________________ 5 Índice de figuras ___________________________________________________ 6 Cap 1 Objetivos y fases de desarrollo__________________________________ 9 Cap 2 Introducción________________________________________________ 10 2.1 Aspectos básicos del titanio y sus aleaciones 2.1.1 Propiedades fundamentales del titanio 2.1.2 Procesos de obtención del titanio 2.1.3 Aleaciones de titanio 2.1.4 Propiedades de las aleaciones del titanio 2.1.5 Propiedades de la aleación Ti-64 2.1.6 Oxidación del titanio. 2.1.7 Aleante Molibdeno 2.1.8 Aleante Niobio 2.2 Tratamientos superficiales 2.3 Proceso de difusión 2.4 Funcionamiento del activador Cap 3 Procedimiento experimental___________________________________ 25 3.1 Materiales empleados 3.2 Preparación de las muestras de Ti 3.3 Preparación del slurry para la difusión 3.4 Difusión sobre el titanio 3.5 Análisis por difracción de rayos X (DRX) 3.6 Recubrimiento de cobre 3.7 Embutición de las piezas 3.8 Análisis de microscopia electrónica de barrido (SEM) 3.9 Software de simulación DICTRA TERMOCALC Cap 4 Resultados__________________________________________________32 4.1 Cálculos previos al experimento utilizando las leyes de Fick. 4.2 Simulación numérica de los experimentos utilizando DICTRA TERMOCALC software 4.3 Resultados experimentales 4.3.1 Resultados de los experimentos realizados a 1100ºC 4.3.2 Resultados de los experimentos realizados a 750º Cap 5 Conclusiones y futuras líneas de investigación______________________67 5.1 Conclusiones 5.2 Futuras líneas de investigación Cap 6 Referencias_________________________________________________ 69
Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of mo... more Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of modified PM Ti surfaces designed for biomedical applications, Powder Metallurgy, 61(2), pp. 90-99.
Boletín de la Sociedad Española de Cerámica y Vidrio
Abstract MAX phases exhibit excellent combination of ceramic and metallic-like properties. In thi... more Abstract MAX phases exhibit excellent combination of ceramic and metallic-like properties. In this work, MAX phase Ti3SiC2 powder was synthesized starting-off with different combinations of elemental powders and carbides. The powders used were Ti, Si, C, SiC and TiC in different combinations, molar ratios and powder size. Powders were heat treated on a vacuum furnace for different times and temperatures for in situ production of the Ti3SiC2 MAX phase. High purity synthesized samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to identify and quantify the different phase constituents present. The main phase constituents in the powders produced were Ti3SiC2 and TiSi2. Up to 94% of Ti3SiC2 MAX phase was obtained using Ti:SiC:C as starting powders in a molar ratio of 3:1.5:0.5. Different phase constitution was observed on the surface and the centre of the samples. An optimal starting powder composition, molar ratio, heat treatment temperature and time is proposed for the formation of high purity Ti3SiC2 MAX phase. Selected mixture was studied thermodynamically and a reaction mechanism of formation of the MAX phase is proposed.
Abstract MAX phase foams could have various applications where tailored functional and mechanical... more Abstract MAX phase foams could have various applications where tailored functional and mechanical properties are required. In this study, Ti2AlC and Ti3SiC2 MAX phase foams with controlled porosity and pore size were produced and characterized. The foams were produced from MAX phase powders by powder metallurgy method using crystalline carbohydrate as a space holder. Foams with overall porosity up to approximately 71 vol% and pore size from 250 μm to 1000 μm were successfully produced; micro-porosity and macro-porosity was characterized. Poisson's ratio and elastic moduli of the foams were measured by resonant ultrasound spectroscopy (RUS) and analyzed as a function of porosity and pore size. Different models were used to fit the experimental data and interpret the effect of pore size and amount of porosity and on elastic properties. It was found that the amount and type of porosity has a larger influence on the elastic properties than the pore size.
MAX phase foams from commercial Ti 2 AlC powder were prepared by a novel powder processing method... more MAX phase foams from commercial Ti 2 AlC powder were prepared by a novel powder processing method using raw sugar as space-holder. Manufacturing MAX phase foams using this method involves mixing Ti 2 AlC powder with raw sugar, pressing the mixture to form a green body followed by space-holder removal and sintering. Green bodies were formed using cold uniaxial pressing and porosity was controlled varying the size and amount of the raw sugar space-holder. Three different space-holder particles sizes in the range of 250-1000 µm and four different volume amounts (20%, 40%, 60% and 80%) of space-holder were studied. The foams produced were characterized, and the size distribution and amount of resulting porosity was compared with the theoretically expected values. Optimal conditions using this novel processing technique for this material were established aiming towards controlling the final microstructures and properties, of porous Ti 2 AlC MAX phase.
Abstract Magnesium disilicide is a narrow gap semiconductor which can be used in several applicat... more Abstract Magnesium disilicide is a narrow gap semiconductor which can be used in several applications such as thermoelectric materials, optoelectronic devices and batteries. It has attracted special attraction because of its low cost and non-toxicity. In the herein examination the formation of this compound is investigated by a simple, one-stage process which is pack cementation. Particularly, the effect of deposition time, activator and donor material concentration was examined. Mg2Si was formed in every case without the presence of other compounds as referred to be present when formed with other coating procedures which have higher cost and are very sophisticated. The examined parameters were found to have effect only on the coating thickness up to a certain value. Moreover, the experimental results confirmed the theoretical thermodynamic calculations performed for this case.
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Papers by S. Tsipas