Josep Picas - Academia.edu (original) (raw)

Papers by Josep Picas

Fundidores: fundiciones ferreas y no ferreas en arena, coquilla y fundición a presión, 2014

Surface & Coatings Technology, Dec 1, 2007

ABSTRACT One of the major problems encountered in hard anodizing cast aluminium alloys is the ina... more ABSTRACT One of the major problems encountered in hard anodizing cast aluminium alloys is the inability to grow a sufficiently thick and homogeneous anodic oxide layer. This work analyzes the possibility of using a semisolid metal forming technology (SSM), like Thixocasting, to solve this surface treatment problem. When compared to conventional castings, Thixocasting reduces porosity and amount of trapped gas, which allow cast components to be heat treated without blistering and the chemical reactivity of the surface also changes. The aim of this work is to study the heat treatment influence on the anodization of A357 aluminium alloy produced by a Thixocasting process. SEM was used to examine the microstructural features found on, within and under the anodized layer. Experiments using a tribometer (ball-on-disc configuration) have been performed in order to evaluate the friction and wear properties of the different layers. The anodic oxide layer formed on the as-cast and T5 substrates had a similar appearance. However, the anodic oxide layer formed over the T6 substrate exhibited a more homogeneous thickness and spheroidized silicon particles became embedded in the anodic oxide layer. Furthermore, the T6 anodized samples showed a slight reduction in friction coefficient and specific wear rate than the as-cast anodized substrate.

Research Square (Research Square), Jun 13, 2023

The design and manufacture of a new mechanical stirring system to obtain a globular structure by ... more The design and manufacture of a new mechanical stirring system to obtain a globular structure by semisolid state forming and its double functionality as a rheometer is presented. The main objective of the Partial Melting Semisolid Manufacturing (PMSM) machine is to obtain a globular microstructure by controlling the viscosity of the A380 second-melt aluminium alloy. In addition, the PMSM device is validated as a rheometer to determine viscosity as a function of temperature. For this purpose, studies were carried out with the same alloy. The results are compared with those obtained for the same conditions with a commercial rheometer. Viscosity control is an innovation compared to traditional mechanical stirring machines, that use time as control parameter. The results of the experimentation gave mainly a dendritic microstructure. However, some rosette/globular microstructure was also obtained in the experiments. This experimentation allows validating the equipment by performing its function optimally.

Thermal spray, May 10, 2004

One of the most important uses of HVOF thermal sprayed CrC-NiCr coatings is for wear resistance. ... more One of the most important uses of HVOF thermal sprayed CrC-NiCr coatings is for wear resistance. In this work Cr3C275-NiCr25 coatings were obtained by high-velocity oxy-fuel system from three agglomerated feedstock powders with various powder size distributions (- 30, -10 and –5 µm). The powders were agglomerated, sintered, plasmafused and crushed, in order to increase their density. The coating microstructures were characterised by SEM microscopy. Differences in coating roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coatings. Experiments using a tribometer (pin on disc configuration) under lubricated and dry conditions have been performed in order to evaluate the friction and wear properties of the different coatings. It was found that the coatings obtained with the lowest feedstock powder size presented the best sliding wear resistance under all the conditions. This fact could be explained in terms of differences of cohesion between the carbide particles and the binder phase. The lower feedstock powder presents a lower carbide particle size that involves a better distribution and cohesion of the chromium carbide with the NiCr binder phase. This fact leads a minor production of “third body” hard particles in the wear tests that influenced quite considerably in the final wear rate of the studied coatings.

Journal of Materials Processing Technology, 2003

International Journal of Material Forming, 2015

High silicon content aluminum alloy (hypereutectic) possess good tribological characteristics wit... more High silicon content aluminum alloy (hypereutectic) possess good tribological characteristics with low coefficients of friction, when embedded with short carbon fiber (Csf), making this composite a good material choice where good wear and high strength properties are required in light weight components.. There is no previously published information available, to the knowledge of the authors, regarding the influence of wear parameters and their interactions on the tribological behavior of Csf reinforced metal matrix composites. In this study a Taguchi design of experiment (DoE) was conducted to optimize and analyze the effects of the wear parameters on the tribological properties of Al/Csf metal matrix composite. A novel thixomixing method which was used to process the metal within the semisolid state was employed to embed short carbon fibers homogenously into the metal matrix. The influences of the sliding speed, applied load and volume fraction, of Csf on the specific wear rate and coefficient of friction were examined, with each of these input parameters tested at three levels(0, 4.2, 8.1 %vol.). The results were indicated that Al/Csf composite had better tribological properties than Al alloy due to which contains carbon as solid lubricant. According to the statistical analysis, the influence of volume fraction of carbon fiber on wear parameters was ranked first; so the load and sliding speed are at the following rankings. The contribution percentage for each parameter was determined by the analysis of variance. The relatively good interfacial adherence of carbon fiber and matrix alloy were demonstrated. The coherent and adherent graphite-rich layer on the worn surface was characterized using scanning electron microscopy (SEM).

AIP Conference Proceedings, 2011

ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure,... more ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC‐CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC‐CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re‐melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.

Semisolid AlSiMg casting alloys are attractive alternatives for automotive and aeronautical appli... more Semisolid AlSiMg casting alloys are attractive alternatives for automotive and aeronautical applications. In this work the effects of heat treatments on hardness and tribological properties of A356 aluminium alloy obtained by Sub-Liquidus Casting (SLC) were studied. The optimum heat treatment conditions, in which the material presents the maximum hardening and wear resistance values, were determined. Heat treatment conditions investigated included: A356 SLC as cast, T5 and T6. Furthermore, AC-46500 and A6061/T6 were analyzed for comparison. The tribological properties of the samples were investigated by pin-on-disc tests at 5 N and 0.05 and 0.1 m•s-1 in dry conditions. The samples were studied by SEM-EDX techniques in order to determine the wear mechanisms and the determination of the products produced during the tests. The maximum hardness and the lowest dry wear rate were obtained through T6 thermal treatment condition.

Surface and Coatings Technology, 2004

The first objective of this paper is to deposit new hard coatings based on compositionally modula... more The first objective of this paper is to deposit new hard coatings based on compositionally modulated CNyTiCNyTiN multilayer films by dual ion beam sputtering using a combination of TiN, TiC and C targets and an Ar-N mixture discharge gas. The 2 second objective is to evaluate the physical and chemical characteristics of the multilayer with respect to their practical applications. In this work, we have studied the composition, morphology, hardness and friction coefficient of the films. The deposition parameters were controlled to obtain films that combine ultrahard behaviour with good tribological and wear properties.

Surface and Coatings Technology, 2003

The effects of three types of substrates (Si, bearing steel, and WC-Co) and acetylene addition (0... more The effects of three types of substrates (Si, bearing steel, and WC-Co) and acetylene addition (0-3.2 vol.% in Ar atmosphere) on the topography, structure, composition, nanohardness and tribological behavior of the High Target Utilization Sputtering W-C coatings were investigated. The results showed that the substrates affected mostly the coating topography, roughness and nanohardness whereas the composition, indentation moduli and coefficients of friction were influenced only by the increase of free carbon content from acetylene addition. Up tõ 5 GPa difference in the hardness of the W-C coatings on Si substrates compared to that on steel was obtained. Simultaneously, methodological problems with the hardness measurements were identified on WC-Co substrate which has the hardness close to that of the coatings. The average values of the coefficient of friction were around 0.3 and slightly decreased at higher carbon contents but the influence of the substrates was small.

International Journal of Refractory Metals and Hard Materials, 2005

The present study describes and compares the mechanical and tribological properties of CrN coatin... more The present study describes and compares the mechanical and tribological properties of CrN coatings deposited by PVD/CAPD (Cathodic Arc Plasma Deposition) on three different substrates: steel, aluminium alloy and reinforced aluminium alloy. The coatingsubstrate interfaces were analysed by scanning electron microscopy (SEM). The ultra-microindentation technique was applied to measure coating hardness. Experiments using a tribometer (pin on disc configuration) under lubricated conditions have been performed in order to evaluate the friction and wear properties of the different systems. The measured coating hardness depends on the indentation depth reached in the ultra-microindentation tests. In this study the coating-substrate system has been characterized, analyzing the hardness variation from the coating to the substrate by different indentation depths, and modelling the experimental curve with a universally approved mathematical model. The CrN-steel system exhibits the best performance, in which the system hardness is close to the CrN coating hardness. The CrN-AMC system performs better than CrN-aluminium but worse than CrN-steel system.

Surface and Coatings Technology

Thermal spray, May 5, 2003

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion a... more Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO2/Y2O3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at a 1000°C for different time periods in order to form the thermally grown oxide (TGO) layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous Al2O3 layer on the top surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating.

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion a... more Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO 2 /Y 2 O 3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at a 1000 o C for different time periods in order to form the thermally grown oxide (TGO) layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous Al 2 O 3 layer on the top surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating.

Journal of Light Metals, May 1, 2002

In this work the a ! b phase transformation, the Ti-0.2Pd alloy undergoes on being subjected to s... more In this work the a ! b phase transformation, the Ti-0.2Pd alloy undergoes on being subjected to several heat treatments has been studied with the aim of improving its properties in order to be used in industrial and biomedical applications. The b phase, intergranular or with a Widmanstt€ a aten type growth, was produced by heat treatment of the alloy in the temperatures range from 750 to 1000°C. The b phase was transformed into a martensitic phase during quenching. The resultant microstructures have been characterized by means of optic and electron microscopy and X-ray analysis. Through the image analysis, a quantitative study of the grain size changes with temperature has been carried out. The influence of the martensitic phase amount and distribution on the mechanical properties of the alloy has been evaluated, with the object of obtaining the best hardness and tensile strength. The samples that were heat treated in the a þ b field show a mechanical properties increase as the amount of martensitic phase rises.

Materials & Design, Dec 1, 2015

A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silico... more A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silicon alloy, for the effective dispersion and distribution of short carbon fibers (C sf) under intensive shear stress (τ) into the eutectic without physical or chemical damage. The C sf were distributed homogeneously into the matrix at optimum conditions: a temperature of 576-580 °C, around 48% of solid fraction, and rotation speed of mixing was at 100 rpm. The gas entrapment and porosity was a challenge in the fabrication the aluminum composite by thixomixing, and its size increased when the samples were heat treated. The extruded and heat treated composites had around 24% improvement of mechanical strength as assessed by tensile tests. The predominant deposition of silicon and its intermetallics at the interfacial region improved the wettability and adherence to achieve good mechanical properties. The formation of some intermetallics can be helpful to overcome low wettability effects and their structural evolutions were impressive. The fractography analysis illustrated the ductile fracture with some plastic deformation as the results of dimples and some fiber pull-out in the fractured surface. Ultra-micro hardness evaluation showed good interfacial bonding after heat treatment. The thixomixing process can be developed to produce various composites with different reinforcement.

Wear, Sep 1, 2006

Automotive manufacturers have specified chromium plating for decades because of its appearance, w... more Automotive manufacturers have specified chromium plating for decades because of its appearance, wear and corrosion resistance, however chromium plating cause effects on human health because of the use of substances in the galvanic process whose toxicological features have not always been recognised. The improvements of the High-Velocity-Oxy-Fuel thermal spray process achieved by Thermico, allow the chromium coating replacement with a comparable or superior surfaces and more environment friendly. The present study describes and compare the mechanical and tribological properties of the conventional and nanostructured HVOF CrC75 (NiCr20) 25 coatings and the conventional hard chromium plating. The objective of the present work is applying this new nanostructured HVOF coating in piston rings and valve stems applications. Furthermore, the studied HVOF coatings are produced with micro and nano-powders in order to avoid the blasting and regrinding operations necessary when plasma spray coatings are used. The coating microstructures were characterised by SEM microscopy. Differences in roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coating. Experiments using a pin on disc tribometer under lubricated and dry conditions have been performed in order to evaluate the friction and wear properties of the different coatings. It was found that the CrC-NiCr coatings obtained with the lowest feedstock powder size presented the best wear resistance under all the studied conditions. The Nano CrC-NiCr coatings have demonstrated superior performance to hard chrome with regard to mechanical and tribological properties, and they can be proposed as an alternative to hard chrome coatings.

Surface & Coatings Technology, Nov 1, 2005

Journal of Alloys and Compounds, Sep 1, 1997

In the present work, experimental research on grain growth kinetics at different temperatures and... more In the present work, experimental research on grain growth kinetics at different temperatures and times of heat ~eahment for titaniam and Ti-0.2Pd in the cx and [3 phases has been carried out. The grain size parameters were obtained by the image analysis technique. The aim of the present study was to quantify the progress of grain growth and the corresponding activation energy for ~x and [3 titanium, and to determine the effect of Palladium. By means of EDS microanalysis, it has been observed that the effect of a higher concentration of palladium on the grain growth is to decrease the growth exponent for the Ti-0.2Pd alloy. The activation energies differ a lot between the two phases oL and 13 for Ti and Ti-0.2Pd. This difference might be due to the different crystal structures,

Fundidores: fundiciones ferreas y no ferreas en arena, coquilla y fundición a presión, 2014

Surface & Coatings Technology, Dec 1, 2007

ABSTRACT One of the major problems encountered in hard anodizing cast aluminium alloys is the ina... more ABSTRACT One of the major problems encountered in hard anodizing cast aluminium alloys is the inability to grow a sufficiently thick and homogeneous anodic oxide layer. This work analyzes the possibility of using a semisolid metal forming technology (SSM), like Thixocasting, to solve this surface treatment problem. When compared to conventional castings, Thixocasting reduces porosity and amount of trapped gas, which allow cast components to be heat treated without blistering and the chemical reactivity of the surface also changes. The aim of this work is to study the heat treatment influence on the anodization of A357 aluminium alloy produced by a Thixocasting process. SEM was used to examine the microstructural features found on, within and under the anodized layer. Experiments using a tribometer (ball-on-disc configuration) have been performed in order to evaluate the friction and wear properties of the different layers. The anodic oxide layer formed on the as-cast and T5 substrates had a similar appearance. However, the anodic oxide layer formed over the T6 substrate exhibited a more homogeneous thickness and spheroidized silicon particles became embedded in the anodic oxide layer. Furthermore, the T6 anodized samples showed a slight reduction in friction coefficient and specific wear rate than the as-cast anodized substrate.

Research Square (Research Square), Jun 13, 2023

The design and manufacture of a new mechanical stirring system to obtain a globular structure by ... more The design and manufacture of a new mechanical stirring system to obtain a globular structure by semisolid state forming and its double functionality as a rheometer is presented. The main objective of the Partial Melting Semisolid Manufacturing (PMSM) machine is to obtain a globular microstructure by controlling the viscosity of the A380 second-melt aluminium alloy. In addition, the PMSM device is validated as a rheometer to determine viscosity as a function of temperature. For this purpose, studies were carried out with the same alloy. The results are compared with those obtained for the same conditions with a commercial rheometer. Viscosity control is an innovation compared to traditional mechanical stirring machines, that use time as control parameter. The results of the experimentation gave mainly a dendritic microstructure. However, some rosette/globular microstructure was also obtained in the experiments. This experimentation allows validating the equipment by performing its function optimally.

Thermal spray, May 10, 2004

One of the most important uses of HVOF thermal sprayed CrC-NiCr coatings is for wear resistance. ... more One of the most important uses of HVOF thermal sprayed CrC-NiCr coatings is for wear resistance. In this work Cr3C275-NiCr25 coatings were obtained by high-velocity oxy-fuel system from three agglomerated feedstock powders with various powder size distributions (- 30, -10 and –5 µm). The powders were agglomerated, sintered, plasmafused and crushed, in order to increase their density. The coating microstructures were characterised by SEM microscopy. Differences in coating roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coatings. Experiments using a tribometer (pin on disc configuration) under lubricated and dry conditions have been performed in order to evaluate the friction and wear properties of the different coatings. It was found that the coatings obtained with the lowest feedstock powder size presented the best sliding wear resistance under all the conditions. This fact could be explained in terms of differences of cohesion between the carbide particles and the binder phase. The lower feedstock powder presents a lower carbide particle size that involves a better distribution and cohesion of the chromium carbide with the NiCr binder phase. This fact leads a minor production of “third body” hard particles in the wear tests that influenced quite considerably in the final wear rate of the studied coatings.

Journal of Materials Processing Technology, 2003

International Journal of Material Forming, 2015

High silicon content aluminum alloy (hypereutectic) possess good tribological characteristics wit... more High silicon content aluminum alloy (hypereutectic) possess good tribological characteristics with low coefficients of friction, when embedded with short carbon fiber (Csf), making this composite a good material choice where good wear and high strength properties are required in light weight components.. There is no previously published information available, to the knowledge of the authors, regarding the influence of wear parameters and their interactions on the tribological behavior of Csf reinforced metal matrix composites. In this study a Taguchi design of experiment (DoE) was conducted to optimize and analyze the effects of the wear parameters on the tribological properties of Al/Csf metal matrix composite. A novel thixomixing method which was used to process the metal within the semisolid state was employed to embed short carbon fibers homogenously into the metal matrix. The influences of the sliding speed, applied load and volume fraction, of Csf on the specific wear rate and coefficient of friction were examined, with each of these input parameters tested at three levels(0, 4.2, 8.1 %vol.). The results were indicated that Al/Csf composite had better tribological properties than Al alloy due to which contains carbon as solid lubricant. According to the statistical analysis, the influence of volume fraction of carbon fiber on wear parameters was ranked first; so the load and sliding speed are at the following rankings. The contribution percentage for each parameter was determined by the analysis of variance. The relatively good interfacial adherence of carbon fiber and matrix alloy were demonstrated. The coherent and adherent graphite-rich layer on the worn surface was characterized using scanning electron microscopy (SEM).

AIP Conference Proceedings, 2011

ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure,... more ABSTRACT In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC‐CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC‐CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re‐melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.

Semisolid AlSiMg casting alloys are attractive alternatives for automotive and aeronautical appli... more Semisolid AlSiMg casting alloys are attractive alternatives for automotive and aeronautical applications. In this work the effects of heat treatments on hardness and tribological properties of A356 aluminium alloy obtained by Sub-Liquidus Casting (SLC) were studied. The optimum heat treatment conditions, in which the material presents the maximum hardening and wear resistance values, were determined. Heat treatment conditions investigated included: A356 SLC as cast, T5 and T6. Furthermore, AC-46500 and A6061/T6 were analyzed for comparison. The tribological properties of the samples were investigated by pin-on-disc tests at 5 N and 0.05 and 0.1 m•s-1 in dry conditions. The samples were studied by SEM-EDX techniques in order to determine the wear mechanisms and the determination of the products produced during the tests. The maximum hardness and the lowest dry wear rate were obtained through T6 thermal treatment condition.

Surface and Coatings Technology, 2004

The first objective of this paper is to deposit new hard coatings based on compositionally modula... more The first objective of this paper is to deposit new hard coatings based on compositionally modulated CNyTiCNyTiN multilayer films by dual ion beam sputtering using a combination of TiN, TiC and C targets and an Ar-N mixture discharge gas. The 2 second objective is to evaluate the physical and chemical characteristics of the multilayer with respect to their practical applications. In this work, we have studied the composition, morphology, hardness and friction coefficient of the films. The deposition parameters were controlled to obtain films that combine ultrahard behaviour with good tribological and wear properties.

Surface and Coatings Technology, 2003

The effects of three types of substrates (Si, bearing steel, and WC-Co) and acetylene addition (0... more The effects of three types of substrates (Si, bearing steel, and WC-Co) and acetylene addition (0-3.2 vol.% in Ar atmosphere) on the topography, structure, composition, nanohardness and tribological behavior of the High Target Utilization Sputtering W-C coatings were investigated. The results showed that the substrates affected mostly the coating topography, roughness and nanohardness whereas the composition, indentation moduli and coefficients of friction were influenced only by the increase of free carbon content from acetylene addition. Up tõ 5 GPa difference in the hardness of the W-C coatings on Si substrates compared to that on steel was obtained. Simultaneously, methodological problems with the hardness measurements were identified on WC-Co substrate which has the hardness close to that of the coatings. The average values of the coefficient of friction were around 0.3 and slightly decreased at higher carbon contents but the influence of the substrates was small.

International Journal of Refractory Metals and Hard Materials, 2005

The present study describes and compares the mechanical and tribological properties of CrN coatin... more The present study describes and compares the mechanical and tribological properties of CrN coatings deposited by PVD/CAPD (Cathodic Arc Plasma Deposition) on three different substrates: steel, aluminium alloy and reinforced aluminium alloy. The coatingsubstrate interfaces were analysed by scanning electron microscopy (SEM). The ultra-microindentation technique was applied to measure coating hardness. Experiments using a tribometer (pin on disc configuration) under lubricated conditions have been performed in order to evaluate the friction and wear properties of the different systems. The measured coating hardness depends on the indentation depth reached in the ultra-microindentation tests. In this study the coating-substrate system has been characterized, analyzing the hardness variation from the coating to the substrate by different indentation depths, and modelling the experimental curve with a universally approved mathematical model. The CrN-steel system exhibits the best performance, in which the system hardness is close to the CrN coating hardness. The CrN-AMC system performs better than CrN-aluminium but worse than CrN-steel system.

Surface and Coatings Technology

Thermal spray, May 5, 2003

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion a... more Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO2/Y2O3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at a 1000°C for different time periods in order to form the thermally grown oxide (TGO) layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous Al2O3 layer on the top surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating.

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion a... more Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO 2 /Y 2 O 3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at a 1000 o C for different time periods in order to form the thermally grown oxide (TGO) layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous Al 2 O 3 layer on the top surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating.

Journal of Light Metals, May 1, 2002

In this work the a ! b phase transformation, the Ti-0.2Pd alloy undergoes on being subjected to s... more In this work the a ! b phase transformation, the Ti-0.2Pd alloy undergoes on being subjected to several heat treatments has been studied with the aim of improving its properties in order to be used in industrial and biomedical applications. The b phase, intergranular or with a Widmanstt€ a aten type growth, was produced by heat treatment of the alloy in the temperatures range from 750 to 1000°C. The b phase was transformed into a martensitic phase during quenching. The resultant microstructures have been characterized by means of optic and electron microscopy and X-ray analysis. Through the image analysis, a quantitative study of the grain size changes with temperature has been carried out. The influence of the martensitic phase amount and distribution on the mechanical properties of the alloy has been evaluated, with the object of obtaining the best hardness and tensile strength. The samples that were heat treated in the a þ b field show a mechanical properties increase as the amount of martensitic phase rises.

Materials & Design, Dec 1, 2015

A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silico... more A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silicon alloy, for the effective dispersion and distribution of short carbon fibers (C sf) under intensive shear stress (τ) into the eutectic without physical or chemical damage. The C sf were distributed homogeneously into the matrix at optimum conditions: a temperature of 576-580 °C, around 48% of solid fraction, and rotation speed of mixing was at 100 rpm. The gas entrapment and porosity was a challenge in the fabrication the aluminum composite by thixomixing, and its size increased when the samples were heat treated. The extruded and heat treated composites had around 24% improvement of mechanical strength as assessed by tensile tests. The predominant deposition of silicon and its intermetallics at the interfacial region improved the wettability and adherence to achieve good mechanical properties. The formation of some intermetallics can be helpful to overcome low wettability effects and their structural evolutions were impressive. The fractography analysis illustrated the ductile fracture with some plastic deformation as the results of dimples and some fiber pull-out in the fractured surface. Ultra-micro hardness evaluation showed good interfacial bonding after heat treatment. The thixomixing process can be developed to produce various composites with different reinforcement.

Wear, Sep 1, 2006

Automotive manufacturers have specified chromium plating for decades because of its appearance, w... more Automotive manufacturers have specified chromium plating for decades because of its appearance, wear and corrosion resistance, however chromium plating cause effects on human health because of the use of substances in the galvanic process whose toxicological features have not always been recognised. The improvements of the High-Velocity-Oxy-Fuel thermal spray process achieved by Thermico, allow the chromium coating replacement with a comparable or superior surfaces and more environment friendly. The present study describes and compare the mechanical and tribological properties of the conventional and nanostructured HVOF CrC75 (NiCr20) 25 coatings and the conventional hard chromium plating. The objective of the present work is applying this new nanostructured HVOF coating in piston rings and valve stems applications. Furthermore, the studied HVOF coatings are produced with micro and nano-powders in order to avoid the blasting and regrinding operations necessary when plasma spray coatings are used. The coating microstructures were characterised by SEM microscopy. Differences in roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coating. Experiments using a pin on disc tribometer under lubricated and dry conditions have been performed in order to evaluate the friction and wear properties of the different coatings. It was found that the CrC-NiCr coatings obtained with the lowest feedstock powder size presented the best wear resistance under all the studied conditions. The Nano CrC-NiCr coatings have demonstrated superior performance to hard chrome with regard to mechanical and tribological properties, and they can be proposed as an alternative to hard chrome coatings.

Surface & Coatings Technology, Nov 1, 2005

Journal of Alloys and Compounds, Sep 1, 1997

In the present work, experimental research on grain growth kinetics at different temperatures and... more In the present work, experimental research on grain growth kinetics at different temperatures and times of heat ~eahment for titaniam and Ti-0.2Pd in the cx and [3 phases has been carried out. The grain size parameters were obtained by the image analysis technique. The aim of the present study was to quantify the progress of grain growth and the corresponding activation energy for ~x and [3 titanium, and to determine the effect of Palladium. By means of EDS microanalysis, it has been observed that the effect of a higher concentration of palladium on the grain growth is to decrease the growth exponent for the Ti-0.2Pd alloy. The activation energies differ a lot between the two phases oL and 13 for Ti and Ti-0.2Pd. This difference might be due to the different crystal structures,