Moara Castro - Academia.edu (original) (raw)

Papers by Moara Castro

Research paper thumbnail of Suppression of mechanical instability in bioabsorbable ultrafine-grained Zn through in-situ stabilization by ZnO nanodispersoids

Journal of Materials Research and Technology

Research paper thumbnail of Architectural design of advanced aluminum matrix composites: a review of recent developments

Critical Reviews in Solid State and Materials Sciences

Research paper thumbnail of Hydrogen Production as a Clean Energy Carrier through Heterojunction Semiconductors for Environmental Remediation

Energies

Today, as a result of the advancement of technology and increasing environmental problems, the ne... more Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is s...

Research paper thumbnail of Development of magnesium-based hybrids through high-pressure torsion

Universidade Federal de Minas Gerais, May 20, 2021

High-pressure torsion (HPT) is a well-established severe plastic deformation technique for achiev... more High-pressure torsion (HPT) is a well-established severe plastic deformation technique for achieving substantial grain refinement and improving mechanical resistance in metallic materials. Besides, HPT can also consolidate metallic particles into a bulk solid disc and incorporate other materials (as hard materials, bioactive materials or other metallic materials) to tailor a variety of hybrids. The present work explores the fabrication of different magnesium matrix hybrids, developed by blending Mg particles with varying kinds of reinforcement, using HPT processing for consolidation. It is shown that hybrids with mechanical integrity can be fabricated by this method. Different characterization techniques, including optical and electron microscopy, are used to analyse the microstructural evolution of the produced hybrids. Well-dispersed second phase particles within continuous and refined magnesium matrix are obtained. The distribution of phases may be controlled by the amount of rotation imposed during processing. The mechanical properties are evaluated by hardness tests and miniature-tensile tests, showing that the composites might display improved strength and tensile resistance, indicating a good bonding of particles. Evidence of a Hall-Petch breakdown was identified in a Mg alloy-alumina hybrid, and higher hardness was achieved in Mg-Zn hybrids due to grain refinement, fragmentation of phases, segregation of alloying elements along grain boundaries and precipitation of intermetallics. The hybrids produced using high-pressure torsion have different potential applications, including the development of bioactive and biodegradable implants.

Research paper thumbnail of Redox reaction in a Mg/Nb2O5 nanocomposite processed by high-pressure torsion

Materials Letters, 2021

Abstract Severe plastic deformation by high-pressure torsion can induce solid-state reactions, in... more Abstract Severe plastic deformation by high-pressure torsion can induce solid-state reactions, including redox reactions, which can affect the mechanical properties of metal matrix composites and hybrids. The present paper shows evidence of a redox reaction between magnesium and nanostructured niobium pentoxide. These chemical reactions release metallic niobium and magnesium oxide. Accordingly, aglomerations of nanocrystalline magnesium oxide is found in the magnesium matrix and a supersaturated solid solution is formed with niobium. Hardness and indentation creep tests show a minor increase in strength and decrease in strain rate sensitivity in the processed material, compared to data for pure magnesium in the literature.

Research paper thumbnail of Mg-Based Composites for Biomedical Applications

Magnesium (Mg) is a promising material for producing temporary orthopedic implants, since it is a... more Magnesium (Mg) is a promising material for producing temporary orthopedic implants, since it is a biodegradable and biocompatible metal which density is very similar to that of the bones. Another benefit is the small strength mismatch when compared to other biocompatible metals, what alleviates stress-shielding effects between bone and the implant. To take advantage of the best materials properties, it is possible to combine magnesium with bioactive ceramics and tailor composites for medical applications with improved biocompatibility, controllable degradation rates and the necessary mechanical properties. To properly insert bioactive reinforcement into the metallic matrix, the fabrication of these composites usually involves at least one high temperature step, as casting or sintering. Yet, recent papers report the development of Mg-based composites at room temperature using severe plastic deformation. This chapter goes through the available data over the development of Mg-composite...

Research paper thumbnail of Using High-pressure Torsion to Consolidate Magnesium Matrix Composites

The high compressive stresses imposed by high pressure torsion allows plastic deformation of mach... more The high compressive stresses imposed by high pressure torsion allows plastic deformation of machine chips and metallic particles until close contact is reached. The severe torsion straining provides the condition for "self-welding" of these particles, creating a continuous metallic matrix. This technique has been used to produce aluminum matrix composites [1, 2] and has also been used to consolidate magnesium particles [3]. Processing magnesium by high pressure torsion is especially interesting since it has been shown that it leads to exceptional ductility [4]. The present work describes the use of high-pressure torsion to consolidate magnesium with reinforcement phases into metal matrix composites. The microstructure of the composite was evaluated by scanning electron microscopy and the mechanical strength was estimated by microhardness testing. It is shown that a dense microstructure is attained after several turns of torsion, and the hardness of the processed composite...

Research paper thumbnail of Estudo da influência da adição de arame frio no processo de soldagem ao arco submerso com dois arames energizados: aspectos operacionais e metalúrgicos

A soldagem ao arco submerso e um processo mecanizado de alta produtividade comumente empregada na... more A soldagem ao arco submerso e um processo mecanizado de alta produtividade comumente empregada na fabricacao de grandes estruturas metalicas. Para atender a crescente demanda da industria, modificacoes na operacao convencional desse processo estao sendo cada vez mais empregadas, a fim de aumentar ainda mais sua capacidade de producao. O presente trabalho aborda uma dessas variacoes, que permite aumentar a taxa de deposicao sem aumentar o consumo de energia atraves da introducao de um arame frio (isolado eletricamente) entre dois arames energizados pela mesma fonte. Essa configuracao foi empregada na soldagem de chapas de aco carbono, com correntes entre 700 e 900 A e razao entre as velocidades de alimentacao dos arames frio e quentes variando de 0 a 1. Os testes foram realizados com o objetivo de avaliar a influencia da adicao do arame frio na morfologia do cordao, nas caracteristicas metalurgicas da solda e na operacionalidade do processo. Os sinais eletricos dos testes experimenta...

Research paper thumbnail of Mechanical mixing of Mg and Zn using high-pressure torsion

Journal of Alloys and Compounds, 2021

Abstract High-pressure torsion (HPT) processing has proved to be a powerful tool to consolidate m... more Abstract High-pressure torsion (HPT) processing has proved to be a powerful tool to consolidate metallic particles and fabricate nanostructured metal-matrix composites with a wide range of compositions. In this study, HPT was used to fabricate different Mg-Zn composites at room temperature, and the evolution of microstructure and mechanical properties were analyzed by x-ray diffraction, scanning and transmission electron microscopy, dynamic hardness and Vickers microhardness tests. The results show that ultrafine-grained microstructures were achieved in all composites compositions. Smaller grain sizes are observed in Mg-rich phases near areas with significant segregations of Zn. The Mg-rich phase appears to retain less deformation than the Zn-rich phase. Bending and vortex phenomena, that are usually reported in microscale for materials mixed by HPT, are observed in nanoscale in this work. There is evidence of the MgZn2 intermetallic phase with a morphology that varies with composition. Higher levels of deformation imposed by HPT leads to an increase in hardening and a decrease in strain-rate sensitivity which are attributed to the tendency to form intermetallics and Zn segregations that prevent grain boundary sliding. Moreover, a model is proposed to explain the mixing of phases in microscale and its relation to the evolution of mechanical properties.

Research paper thumbnail of Corrosion Behavior in Hank's Solution of a Magnesium–Hydroxyapatite Composite Processed by High‐Pressure Torsion

Advanced Engineering Materials, 2020

It is known that magnesium (Mg)-hydroxyapatite (HA) composites can be produced by the room temper... more It is known that magnesium (Mg)-hydroxyapatite (HA) composites can be produced by the room temperature consolidation of particles. The present study analyzes the corrosion behavior of an Mg-HA composite and makes a direct comparison with pure Mg. Samples of Mg-HA and of pure Mg were immersed in Hank`s solution for up to 60 hours and the microstructure and corrosion products were characterized by scanning and transmission electron microscopy and X-ray diffraction. Electrochemical tests were used to evaluate the corrosion behavior and a hydrogen evolution test was undertaken to determine the corrosion rate. The results show the corrosion rate of the Mg-HA composite is higher than for pure Mg but decreases significantly after ~10 hours of immersion in Hank`s solution. The increase in corrosion resistance of the composite is attributed to the formation of a protective layer of corrosion products with an external surface layer rich in Ca, P and O.

Research paper thumbnail of Developing magnesium-based composites through high-pressure torsion

Letters on Materials, 2019

Magnesium and its alloys display interesting properties such as low density and biocompatibility ... more Magnesium and its alloys display interesting properties such as low density and biocompatibility but the lack of ductility and low strength compromise their performance in many applications. Fabrication of metal matrix composites may alleviate these challenges and improve overall performance. Magnesium matrix composites can be produced by cold consolidation of particles through high-pressure torsion and this paper summarizes recent findings in processing routes for the fabrication of composites, the microstructure developed, mechanical properties obtained and potential applications. It is shown that ductile materials can be mixed with magnesium by processing half samples placed side by side and hard and brittle materials can be incorporated by processing mixed particles. The distribution of phases may be controlled by the amount of rotation imposed during processing. Well-dispersed second phase particles within a continuous magnesium matrix can be obtained. Thus, it is possible to incorporate bioactive materials within a biodegradable magnesium matrix. Detailed characterization using transmission electron microscopy reveals the processing also refines the grain structure of the metallic matrix. The composites may display good ductility, improved strength and an ability to precipitate intermetallics through thermal treatment. The composites produced using high-pressure torsion have different potential applications including the development of bioactive and biodegradable biological implants.

Research paper thumbnail of Consolidation of magnesium and magnesium-quasicrystal composites through high‑pressure torsion

Letters on Materials, 2019

It is of great interest to produce magnesium-based composites through room temperature consolidat... more It is of great interest to produce magnesium-based composites through room temperature consolidation of particles using highpressure torsion. However, the lack of bonding between the particles compromises the integrity and ductility of such materials. The present work evaluates the microstructure of the composites involving pure magnesium and a magnesium alloy AZ91 with the incorporation of quasicrystal particles as a reinforcement phase. Thus, an Al-Cu-Fe icosahedral quasicrystalline alloy was produced by gas atomization and mixed with magnesium particles in a proportion of 80 % in weight of metal and 20 % of quasicrystal. The mix was processed by different number of turns of high-pressure torsion. The microstructure was observed using scanning electron microscopy and the mechanical behavior was evaluated using tensile testing. Generalized lack of bonding is observed in the AZ91 alloy matrix composite and localized lack of bonding in the pure magnesium matrix. High tensile strength has been achieved after consolidation of pure magnesium with and without quasicrystal reinforcement but all samples display limited ductility. The elongations are less than 5 % in all conditions. This is attributed to pre-existing areas with lack of bonding in the matrix, cracking of the hard particles and lack of bonding between the matrix and the reinforcement particles.

Research paper thumbnail of Inverse Hall–Petch Behaviour in an AZ91 Alloy and in an AZ91–Al 2 O 3 Composite Consolidated by High‐Pressure Torsion

Advanced Engineering Materials, 2019

Research paper thumbnail of Magnesium-Based Bioactive Composites Processed at Room Temperature

Materials, 2019

Hydroxyapatite and bioactive glass particles were added to pure magnesium and an AZ91 magnesium a... more Hydroxyapatite and bioactive glass particles were added to pure magnesium and an AZ91 magnesium alloy and then consolidated into disc-shaped samples at room temperature using high-pressure torsion (HPT). The bioactive particles appeared well-dispersed in the metal matrix after multiple turns of HPT. Full consolidation was attained using pure magnesium, but the center of the AZ91 disc failed to fully consolidate even after 50 turns. The magnesium-hydroxyapatite composite displayed an ultimate tensile strength above 150 MPa, high cell viability, and a decreasing rate of corrosion during immersion in Hank’s solution. The composites produced with bioactive glass particles exhibited the formation of calcium phosphate after 2 h of immersion in Hank’s solution and there was rapid corrosion in these materials.

Research paper thumbnail of A magnesium-aluminium composite produced by high-pressure torsion

Journal of Alloys and Compounds, 2019

A magnesium / aluminium composite was produced by room temperature consolidation through high-pre... more A magnesium / aluminium composite was produced by room temperature consolidation through high-pressure torsion (HPT) processing. Half-discs of the pure metals were placed side-by-side and subjected to different numbers of turns. The initially reduced interface between the phases gradually increased with increasing rotation. The composite displayed a significant ductility even after 10 turns. The distribution of hardness in the HPT-processed discs was bi-modal in the early stages of processing. As the number of turns increased and the thickness of the phases decreased there was a noticeable increase in hardness. The hardness values of the composite further increased after thermal treatment due to the formation of intermetallics within the interface between the magnesium and aluminium-rich phases.

Research paper thumbnail of Consolidation of Magnesium and Magnesium Alloy Machine Chips Using High-Pressure Torsion

Materials Science Forum, 2018

The high-pressure torsion processing technique was used to consolidate and process magnesium-base... more The high-pressure torsion processing technique was used to consolidate and process magnesium-based chips. Chips were prepared by machining commercially pure magnesium and a magnesium alloy AZ91 separately. Optical microscopy and microhardness measurements showed good consolidation of pure magnesium. The magnesium alloy continued to exhibit the boundaries between the chips even after 5 turns of HPT suggesting poor bonding. The results show that soft chips are easier to consolidate through HPT than harder alloys.

Research paper thumbnail of Development of a magnesium-alumina composite through cold consolidation of machining chips by high-pressure torsion

Journal of Alloys and Compounds, 2018

High pressure torsion offers unique conditions for the consolidation of metallic particles at roo... more High pressure torsion offers unique conditions for the consolidation of metallic particles at room temperature owing to the high hydrostatic compressive stresses combined with the high shear strain. A Mg-Al 2 O 3 composite was produced by consolidation of machining chips of pure magnesium with 10% in volume of alumina particles. The consolidation process was investigated by optical and scanning electron microscopy and X-ray microtomography. It is shown that shear deformation concentrates along thick alumina particle layers in the initial stage of deformation. A significant fraction of the hard phase particles are pushed into the outflow in quasiconstrained HPT and a homogeneous composite is achieved after significant straining. The composite exhibits a refined microstructure, a higher hardness and improved resistance against room temperature creep compared to pure magnesium.

Research paper thumbnail of Suppression of mechanical instability in bioabsorbable ultrafine-grained Zn through in-situ stabilization by ZnO nanodispersoids

Journal of Materials Research and Technology

Research paper thumbnail of Architectural design of advanced aluminum matrix composites: a review of recent developments

Critical Reviews in Solid State and Materials Sciences

Research paper thumbnail of Hydrogen Production as a Clean Energy Carrier through Heterojunction Semiconductors for Environmental Remediation

Energies

Today, as a result of the advancement of technology and increasing environmental problems, the ne... more Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is s...

Research paper thumbnail of Development of magnesium-based hybrids through high-pressure torsion

Universidade Federal de Minas Gerais, May 20, 2021

High-pressure torsion (HPT) is a well-established severe plastic deformation technique for achiev... more High-pressure torsion (HPT) is a well-established severe plastic deformation technique for achieving substantial grain refinement and improving mechanical resistance in metallic materials. Besides, HPT can also consolidate metallic particles into a bulk solid disc and incorporate other materials (as hard materials, bioactive materials or other metallic materials) to tailor a variety of hybrids. The present work explores the fabrication of different magnesium matrix hybrids, developed by blending Mg particles with varying kinds of reinforcement, using HPT processing for consolidation. It is shown that hybrids with mechanical integrity can be fabricated by this method. Different characterization techniques, including optical and electron microscopy, are used to analyse the microstructural evolution of the produced hybrids. Well-dispersed second phase particles within continuous and refined magnesium matrix are obtained. The distribution of phases may be controlled by the amount of rotation imposed during processing. The mechanical properties are evaluated by hardness tests and miniature-tensile tests, showing that the composites might display improved strength and tensile resistance, indicating a good bonding of particles. Evidence of a Hall-Petch breakdown was identified in a Mg alloy-alumina hybrid, and higher hardness was achieved in Mg-Zn hybrids due to grain refinement, fragmentation of phases, segregation of alloying elements along grain boundaries and precipitation of intermetallics. The hybrids produced using high-pressure torsion have different potential applications, including the development of bioactive and biodegradable implants.

Research paper thumbnail of Redox reaction in a Mg/Nb2O5 nanocomposite processed by high-pressure torsion

Materials Letters, 2021

Abstract Severe plastic deformation by high-pressure torsion can induce solid-state reactions, in... more Abstract Severe plastic deformation by high-pressure torsion can induce solid-state reactions, including redox reactions, which can affect the mechanical properties of metal matrix composites and hybrids. The present paper shows evidence of a redox reaction between magnesium and nanostructured niobium pentoxide. These chemical reactions release metallic niobium and magnesium oxide. Accordingly, aglomerations of nanocrystalline magnesium oxide is found in the magnesium matrix and a supersaturated solid solution is formed with niobium. Hardness and indentation creep tests show a minor increase in strength and decrease in strain rate sensitivity in the processed material, compared to data for pure magnesium in the literature.

Research paper thumbnail of Mg-Based Composites for Biomedical Applications

Magnesium (Mg) is a promising material for producing temporary orthopedic implants, since it is a... more Magnesium (Mg) is a promising material for producing temporary orthopedic implants, since it is a biodegradable and biocompatible metal which density is very similar to that of the bones. Another benefit is the small strength mismatch when compared to other biocompatible metals, what alleviates stress-shielding effects between bone and the implant. To take advantage of the best materials properties, it is possible to combine magnesium with bioactive ceramics and tailor composites for medical applications with improved biocompatibility, controllable degradation rates and the necessary mechanical properties. To properly insert bioactive reinforcement into the metallic matrix, the fabrication of these composites usually involves at least one high temperature step, as casting or sintering. Yet, recent papers report the development of Mg-based composites at room temperature using severe plastic deformation. This chapter goes through the available data over the development of Mg-composite...

Research paper thumbnail of Using High-pressure Torsion to Consolidate Magnesium Matrix Composites

The high compressive stresses imposed by high pressure torsion allows plastic deformation of mach... more The high compressive stresses imposed by high pressure torsion allows plastic deformation of machine chips and metallic particles until close contact is reached. The severe torsion straining provides the condition for "self-welding" of these particles, creating a continuous metallic matrix. This technique has been used to produce aluminum matrix composites [1, 2] and has also been used to consolidate magnesium particles [3]. Processing magnesium by high pressure torsion is especially interesting since it has been shown that it leads to exceptional ductility [4]. The present work describes the use of high-pressure torsion to consolidate magnesium with reinforcement phases into metal matrix composites. The microstructure of the composite was evaluated by scanning electron microscopy and the mechanical strength was estimated by microhardness testing. It is shown that a dense microstructure is attained after several turns of torsion, and the hardness of the processed composite...

Research paper thumbnail of Estudo da influência da adição de arame frio no processo de soldagem ao arco submerso com dois arames energizados: aspectos operacionais e metalúrgicos

A soldagem ao arco submerso e um processo mecanizado de alta produtividade comumente empregada na... more A soldagem ao arco submerso e um processo mecanizado de alta produtividade comumente empregada na fabricacao de grandes estruturas metalicas. Para atender a crescente demanda da industria, modificacoes na operacao convencional desse processo estao sendo cada vez mais empregadas, a fim de aumentar ainda mais sua capacidade de producao. O presente trabalho aborda uma dessas variacoes, que permite aumentar a taxa de deposicao sem aumentar o consumo de energia atraves da introducao de um arame frio (isolado eletricamente) entre dois arames energizados pela mesma fonte. Essa configuracao foi empregada na soldagem de chapas de aco carbono, com correntes entre 700 e 900 A e razao entre as velocidades de alimentacao dos arames frio e quentes variando de 0 a 1. Os testes foram realizados com o objetivo de avaliar a influencia da adicao do arame frio na morfologia do cordao, nas caracteristicas metalurgicas da solda e na operacionalidade do processo. Os sinais eletricos dos testes experimenta...

Research paper thumbnail of Mechanical mixing of Mg and Zn using high-pressure torsion

Journal of Alloys and Compounds, 2021

Abstract High-pressure torsion (HPT) processing has proved to be a powerful tool to consolidate m... more Abstract High-pressure torsion (HPT) processing has proved to be a powerful tool to consolidate metallic particles and fabricate nanostructured metal-matrix composites with a wide range of compositions. In this study, HPT was used to fabricate different Mg-Zn composites at room temperature, and the evolution of microstructure and mechanical properties were analyzed by x-ray diffraction, scanning and transmission electron microscopy, dynamic hardness and Vickers microhardness tests. The results show that ultrafine-grained microstructures were achieved in all composites compositions. Smaller grain sizes are observed in Mg-rich phases near areas with significant segregations of Zn. The Mg-rich phase appears to retain less deformation than the Zn-rich phase. Bending and vortex phenomena, that are usually reported in microscale for materials mixed by HPT, are observed in nanoscale in this work. There is evidence of the MgZn2 intermetallic phase with a morphology that varies with composition. Higher levels of deformation imposed by HPT leads to an increase in hardening and a decrease in strain-rate sensitivity which are attributed to the tendency to form intermetallics and Zn segregations that prevent grain boundary sliding. Moreover, a model is proposed to explain the mixing of phases in microscale and its relation to the evolution of mechanical properties.

Research paper thumbnail of Corrosion Behavior in Hank's Solution of a Magnesium–Hydroxyapatite Composite Processed by High‐Pressure Torsion

Advanced Engineering Materials, 2020

It is known that magnesium (Mg)-hydroxyapatite (HA) composites can be produced by the room temper... more It is known that magnesium (Mg)-hydroxyapatite (HA) composites can be produced by the room temperature consolidation of particles. The present study analyzes the corrosion behavior of an Mg-HA composite and makes a direct comparison with pure Mg. Samples of Mg-HA and of pure Mg were immersed in Hank`s solution for up to 60 hours and the microstructure and corrosion products were characterized by scanning and transmission electron microscopy and X-ray diffraction. Electrochemical tests were used to evaluate the corrosion behavior and a hydrogen evolution test was undertaken to determine the corrosion rate. The results show the corrosion rate of the Mg-HA composite is higher than for pure Mg but decreases significantly after ~10 hours of immersion in Hank`s solution. The increase in corrosion resistance of the composite is attributed to the formation of a protective layer of corrosion products with an external surface layer rich in Ca, P and O.

Research paper thumbnail of Developing magnesium-based composites through high-pressure torsion

Letters on Materials, 2019

Magnesium and its alloys display interesting properties such as low density and biocompatibility ... more Magnesium and its alloys display interesting properties such as low density and biocompatibility but the lack of ductility and low strength compromise their performance in many applications. Fabrication of metal matrix composites may alleviate these challenges and improve overall performance. Magnesium matrix composites can be produced by cold consolidation of particles through high-pressure torsion and this paper summarizes recent findings in processing routes for the fabrication of composites, the microstructure developed, mechanical properties obtained and potential applications. It is shown that ductile materials can be mixed with magnesium by processing half samples placed side by side and hard and brittle materials can be incorporated by processing mixed particles. The distribution of phases may be controlled by the amount of rotation imposed during processing. Well-dispersed second phase particles within a continuous magnesium matrix can be obtained. Thus, it is possible to incorporate bioactive materials within a biodegradable magnesium matrix. Detailed characterization using transmission electron microscopy reveals the processing also refines the grain structure of the metallic matrix. The composites may display good ductility, improved strength and an ability to precipitate intermetallics through thermal treatment. The composites produced using high-pressure torsion have different potential applications including the development of bioactive and biodegradable biological implants.

Research paper thumbnail of Consolidation of magnesium and magnesium-quasicrystal composites through high‑pressure torsion

Letters on Materials, 2019

It is of great interest to produce magnesium-based composites through room temperature consolidat... more It is of great interest to produce magnesium-based composites through room temperature consolidation of particles using highpressure torsion. However, the lack of bonding between the particles compromises the integrity and ductility of such materials. The present work evaluates the microstructure of the composites involving pure magnesium and a magnesium alloy AZ91 with the incorporation of quasicrystal particles as a reinforcement phase. Thus, an Al-Cu-Fe icosahedral quasicrystalline alloy was produced by gas atomization and mixed with magnesium particles in a proportion of 80 % in weight of metal and 20 % of quasicrystal. The mix was processed by different number of turns of high-pressure torsion. The microstructure was observed using scanning electron microscopy and the mechanical behavior was evaluated using tensile testing. Generalized lack of bonding is observed in the AZ91 alloy matrix composite and localized lack of bonding in the pure magnesium matrix. High tensile strength has been achieved after consolidation of pure magnesium with and without quasicrystal reinforcement but all samples display limited ductility. The elongations are less than 5 % in all conditions. This is attributed to pre-existing areas with lack of bonding in the matrix, cracking of the hard particles and lack of bonding between the matrix and the reinforcement particles.

Research paper thumbnail of Inverse Hall–Petch Behaviour in an AZ91 Alloy and in an AZ91–Al 2 O 3 Composite Consolidated by High‐Pressure Torsion

Advanced Engineering Materials, 2019

Research paper thumbnail of Magnesium-Based Bioactive Composites Processed at Room Temperature

Materials, 2019

Hydroxyapatite and bioactive glass particles were added to pure magnesium and an AZ91 magnesium a... more Hydroxyapatite and bioactive glass particles were added to pure magnesium and an AZ91 magnesium alloy and then consolidated into disc-shaped samples at room temperature using high-pressure torsion (HPT). The bioactive particles appeared well-dispersed in the metal matrix after multiple turns of HPT. Full consolidation was attained using pure magnesium, but the center of the AZ91 disc failed to fully consolidate even after 50 turns. The magnesium-hydroxyapatite composite displayed an ultimate tensile strength above 150 MPa, high cell viability, and a decreasing rate of corrosion during immersion in Hank’s solution. The composites produced with bioactive glass particles exhibited the formation of calcium phosphate after 2 h of immersion in Hank’s solution and there was rapid corrosion in these materials.

Research paper thumbnail of A magnesium-aluminium composite produced by high-pressure torsion

Journal of Alloys and Compounds, 2019

A magnesium / aluminium composite was produced by room temperature consolidation through high-pre... more A magnesium / aluminium composite was produced by room temperature consolidation through high-pressure torsion (HPT) processing. Half-discs of the pure metals were placed side-by-side and subjected to different numbers of turns. The initially reduced interface between the phases gradually increased with increasing rotation. The composite displayed a significant ductility even after 10 turns. The distribution of hardness in the HPT-processed discs was bi-modal in the early stages of processing. As the number of turns increased and the thickness of the phases decreased there was a noticeable increase in hardness. The hardness values of the composite further increased after thermal treatment due to the formation of intermetallics within the interface between the magnesium and aluminium-rich phases.

Research paper thumbnail of Consolidation of Magnesium and Magnesium Alloy Machine Chips Using High-Pressure Torsion

Materials Science Forum, 2018

The high-pressure torsion processing technique was used to consolidate and process magnesium-base... more The high-pressure torsion processing technique was used to consolidate and process magnesium-based chips. Chips were prepared by machining commercially pure magnesium and a magnesium alloy AZ91 separately. Optical microscopy and microhardness measurements showed good consolidation of pure magnesium. The magnesium alloy continued to exhibit the boundaries between the chips even after 5 turns of HPT suggesting poor bonding. The results show that soft chips are easier to consolidate through HPT than harder alloys.

Research paper thumbnail of Development of a magnesium-alumina composite through cold consolidation of machining chips by high-pressure torsion

Journal of Alloys and Compounds, 2018

High pressure torsion offers unique conditions for the consolidation of metallic particles at roo... more High pressure torsion offers unique conditions for the consolidation of metallic particles at room temperature owing to the high hydrostatic compressive stresses combined with the high shear strain. A Mg-Al 2 O 3 composite was produced by consolidation of machining chips of pure magnesium with 10% in volume of alumina particles. The consolidation process was investigated by optical and scanning electron microscopy and X-ray microtomography. It is shown that shear deformation concentrates along thick alumina particle layers in the initial stage of deformation. A significant fraction of the hard phase particles are pushed into the outflow in quasiconstrained HPT and a homogeneous composite is achieved after significant straining. The composite exhibits a refined microstructure, a higher hardness and improved resistance against room temperature creep compared to pure magnesium.