Jagadeesh Sure | Vellore Institute of Technology (original) (raw)

Papers by Jagadeesh Sure

Ceramics International, 2012

... Jagadeesh Sure, A. Ravi Shankar, S. Ramya, U. Kamachi Mudali Corresponding Author Contact Inf... more ... Jagadeesh Sure, A. Ravi Shankar, S. Ramya, U. Kamachi Mudali Corresponding Author Contact Information , E-mail The Corresponding Author. ... and permeability towards oxygen was reduced by thermal spraying of Al 2 O 3 , ZrO 2 with different bond coats (SiC or Cr 3 C 2 ) [20 ...

Surface Review and Letters

Energies

Carbon nanotubes (CNTs) are being increasingly studied as electrode materials for supercapacitors... more Carbon nanotubes (CNTs) are being increasingly studied as electrode materials for supercapacitors (SCs) due to their high electronic conductivity and chemical and mechanical stability. However, their energy density and specific capacitance have not reached the commercial stage due to their electrostatic charge storage system via a non-faradic mechanism. Moreover, magnetite (Fe3O4) exhibits higher specific capacitance originating from its pseudocapacitive behaviour, while it has irreversible volume expansion during cycling. Therefore, a very interesting and facile strategy to arrive at better performance and stability is to integrate CNTs and Fe3O4. In this study, we demonstrate the microwave-solvothermal process for the synthesis of Fe3O4 nanoparticles uniformly grown on a CNT composite as an electrode for SCs. The synthesized Fe3O4/CNT composite delivers a reversible capacitance of 187.1 F/g at 1 A/g, superior rate capability by maintaining 61.6% of 10 A/g (vs. 1 A/g), and cycling ...

Metallurgical and Materials Transactions B, 2021

The study has aimed at understanding the key factors involved in the synthesis of porous Ti-based... more The study has aimed at understanding the key factors involved in the synthesis of porous Ti-based β-Ti-35Nb-7.9Sn alloy by electro-deoxidation of compacted and sintered TiO2-Nb2O5-SnO2 mixed oxide disks in molten calcium chloride. Processing parameters assessed were the sintering temperature, and thus, the open porosity, of the oxide precursor as well as the temperature, voltage, and time of electro-deoxidation. Process conditions were arrived at that enable the complete and efficient reduction of the mixed oxide. The Ti-35Nb-7.9Sn alloy product was single-phase bcc and had a porous microstructure with nodular particles. Electro-deoxidation experiments of different durations allowed the identification of the main intermediate phases occurring during the reduction as well as the mechanism of the oxide-to-alloy conversion. The porous Ti-35Nb-7.9Sn alloy prepared was subjected to corrosion testing in Hanks’ simulated body fluid solution and was found to exhibit superior performance when compared with dense 304L and 316L steels and brass.

Electrochimica Acta, 2021

Lithium-sulfur batteries have shown increasing promise for high energy densities and reduced cost... more Lithium-sulfur batteries have shown increasing promise for high energy densities and reduced costs. Facile sulfur loading techniques demonstrate a critical way to achieving high dispersions of sulfur in the host's matrix, improving conductivity and simultaneously decreasing the active mass loss from the cathode. Here we investigate the effect of sulfur loading methods on the electrochemical performance of porous carbon/sulfur composites containing approximately 70 wt% sulfur. Three different loading techniques are tested, including one-step molten sulfur impregnation (155 °C), two-step molten sulfur impregnation (155 °C + 300 °C) and a sulfur organic solution impregnation, in which the entire microporous volume of carbon is filled by sulfur. It is found that the simple sulfur organic solution impregnation method is the most effective in enhancing the electrochemical performance of the hierarchical porous carbon/sulfur composite cathode in the lithium-sulfur battery system, due to the weaker interaction occurring between the sulfur and microporous carbon. Our work demonstrates the impact of sulfur loading method on the electrochemical performance of lithium-sulfur batteries, which offers new insights into the preparation technology of electrodes.

Materials Today Communications, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Angewandte Chemie, 2020

High-entropy alloys and compounds are becoming an important class of new materials due to their o... more High-entropy alloys and compounds are becoming an important class of new materials due to their outstanding refractory and high-temperature properties. However, preparation in bulk quantities and in powder form via classical metallurgical methods is challenging. Here, we report the first-time synthesis of an ultra-high-temperature highentropy carbide, (TiNbTaZrHf)C, via a facile electrochemical process. In this, a mixture of the individual metal oxides and graphite is deoxidised in a melt of CaCl2 at a temperature of only 1173 K. The (TiNbTaZrHf)C prepared is single-phase fcc and has a powdery morphology with a particle size range of 15-80 nm. Such materials are in demand for modern additive manufacturing techniques while preliminary tests have also indicated a possible application in supercapacitors. The successful synthesis of (TiNbTaZrHf)C powder may now guide the way towards establishing the electrochemical route for the preparation of many other entropy-stabilised materials.

Journal of The Electrochemical Society, 2020

The cost of tantalum (Ta), and thus of Ta capacitors, is undesirably high owing to the limited av... more The cost of tantalum (Ta), and thus of Ta capacitors, is undesirably high owing to the limited availability of its ores and the energy-intensive production. Reported herein is the economically viable electrochemical synthesis of Ta-Nb alloys as a potential replacement for Ta in capacitors. Ta-xNb (x = 20, 50, 80) alloys were prepared directly by electro-deoxidation of Ta2O5-Nb2O5 mixed oxide disks in CaCl2 melt at 900 °C and the results were compared with those for the pure metals. The alloys and metals thus made were in the form of powders and consisted solely of the body-centered cubic phase. The overall compositions of the alloys were close to the target values. EDX and XPS analyses revealed that the particles underwent surface oxidation during the post-electrolytic washing process, thereby forming the required dielectric coating around the metallic cores. Cyclic voltammetry in an aqueous electrolytic cell demonstrated that all powders behaved as typical capacitor materials. TG/D...

Energy Storage Materials, 2019

Solid state electrochemically synthesised β-SiC nanowires as the anode material in lithium ion ba... more Solid state electrochemically synthesised β-SiC nanowires as the anode material in lithium ion batteries Energy Storage Materials,

Journal of The Electrochemical Society, 2018

Silicon carbide was synthesized from mixtures of SiO 2 and graphite by applying the concept of th... more Silicon carbide was synthesized from mixtures of SiO 2 and graphite by applying the concept of the FFC-Cambridge process and several fundamental aspects of the synthesis route were investigated. Porous disks composed of powders of SiO 2 and graphite in molar ratios of 1:0.5, 1:1 and 1:1.5 were prepared by sintering in inert atmosphere and subjected to electro-deoxidation in molten CaCl 2 at 1173 K under a range of experimental conditions. Disks of molar ratio 1:1.5, reduced at an applied voltage of 2.8 V for a duration of 6 h, yielded exclusively phase-pure SiC of nanowire morphology as the reaction product, while the other precursor compositions provided significant amounts of calcium silicides. Voltages lower than 2.8 V gave mixtures of SiC with elemental Si and graphite, and voltages higher than that gave CaSi alone. Shorter electro-deoxidation times led to incomplete reduction and allowed for the identification of CaSiO 3 as a transient phase. Based on the experimental results a multipath reaction mechanism is proposed, consisting of the electrochemical reduction of SiO 2 and CaSiO 3 to Si and the subsequent in-situ carbonization of the Si formed to SiC. The effect of N 2 at high temperature on the electrochemically synthesized SiC was investigated and the formation of nanowire Si 2 N 2 O was observed. Overall, the process presented is a facile single-step and low-temperature method for the synthesis of SiC with possible commercial prospects.

MATERIALS TRANSACTIONS, 2019

TixNbySn alloys with different Nb and Sn contents, of x = 24, 35, 42 mass% and y = 4, 7.9 mass%, ... more TixNbySn alloys with different Nb and Sn contents, of x = 24, 35, 42 mass% and y = 4, 7.9 mass%, were synthesised directly from TiO 2 , Nb 2 O 5 and SnO 2 mixtures via the FFC-Cambridge process. Compacted powder discs were employed as the cathode versus graphite as the anode in molten CaCl 2 as the electrolyte. XRD analysis of the as-synthesised alloys showed that the two alloys with Nb content of 24 mass% were dual-phase ¡/¢-Ti whereas the other four alloys with Nb contents of 35 and 42 mass% were single-phase ¢-Ti. SEM analysis showed that the alloys were highly porous, and that particle size decreased with increase in Nb and Sn contents. Alloy samples of each composition were subjected to short-term and long-term immersion tests in Hanks' simulated body fluid solution. XPS studies then identified a passive oxide film on the surface of the alloy, and a hydroxyapatite layer on top of the oxide. Potentiodynamic polarisation studies revealed excellent corrosion resistance with very small corrosion current densities despite high open porosities. Furthermore, alloy samples were subjected to heat treatment in vacuum. Mechanical testing of these identified a substantial increase of elastic modulus and Vickers hardness. Overall, the experimental programme has brought out that the properties of the TiNbSn alloys prepared are influenced markedly by their Nb and Sn contents, and that single-phase ¢-Ti35Nb4Sn holds promise as a candidate material for body implant applications.

MATERIALS TRANSACTIONS, 2019

Alloy of composition Ti5Ta2Nb (numbers in mass%) was synthesised directly from the corresponding ... more Alloy of composition Ti5Ta2Nb (numbers in mass%) was synthesised directly from the corresponding mixed metal oxides via the FFC-Cambridge process. Compacted powder discs of TiO 2 Ta 2 O 5 Nb 2 O 5 were cathodically polarised against a graphite anode in a molten CaCl 2 electrolyte, and the effect of various process parameters on the synthesis of the alloy was investigated. The samples retained their disc-type shape throughout the oxide-to-metal conversion under appropriate processing conditions. XRD analysis showed that the electrochemically prepared alloy existed as single-phase ¡-Ti and changed into dual-phase (¡+¢)-Ti upon heat treatment. SEM/EDX analysis revealed a nodular porous microstructure and confirmed the intended chemical composition. Backscattered SEM analysis after heat treatment provided direct evidence of micron-sized ¢-phase precipitates at the boundaries of the ¡-phase particles. Microhardness of the heat-treated alloy compared well with literature data for the same material prepared by conventional metallurgical methods. Overall, the study has demonstrated the feasibility of the single-step electrochemical fabrication of Ti5Ta2Nb alloy bodies directly from oxides for structural application.

Journal of Alloys and Compounds, 2019

Single-phase equiatomic CoCrFeNi high-entropy alloy has been synthesised by direct electrochemica... more Single-phase equiatomic CoCrFeNi high-entropy alloy has been synthesised by direct electrochemical reduction from oxide precursors according to the concept of the FFC-Cambridge process. Metal oxide mixtures were heat treated in air to provide a blend of spinels, which were then employed as the cathode in the electro-deoxidation process. Melts of eutectic CaCl 2-NaCl and pure CaCl 2 were used as the electrolytes. Varying the experimental conditions in terms of processing temperature and time yielded CoCrFeNi alloys of diverse morphologies, ranging from fine dispersed powders to solid threedimensional objects, as they are of relevance for additive manufacturing and near-netshape fabrication. Notably, all solid alloy samples exhibited a higher hardness than calculated by the rule of mixture, despite the presence of significant residual porosity. The results highlight the versatility of the FFC-Cambridge process for alloy preparation and suggest the possibility of economically viable large-scale manufacture of steel-type highentropy alloys.

Materials Science and Engineering: C, 2018

Porous titanium-niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by el... more Porous titanium-niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO2 and Nb2O5 powders in molten CaCl2 at 1173 K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase α/β-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase β-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310 K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the bestsuited candidate of the materials studied in regard to biomedical applications.

Transactions of the Indian Institute of Metals, 2016

Plasma sprayed alumina–40 wt% titania (A40T) coatings deposited on high density graphite were las... more Plasma sprayed alumina–40 wt% titania (A40T) coatings deposited on high density graphite were laser melted and immersed in molten LiCl–KCl salt for 24 h at 873 K to compare the corrosion behavior of the coatings before and after laser surface treatment. The as-sprayed and laser melted coatings after exposure to molten salt were characterized to evaluate their microstructure and phase composition. Uniform microstructure and homogeneous surface generated by laser melting process facilitated enhanced protection of the A40T coatings from molten salt attack. Absence of phase change in the coating after corrosion test, implied that no reaction occurred between the molten salt and coating. While keeping other beam parameters constant, increasing the laser average power from 6.4 to 8 W had not only resulted in improving the surface quality and the corrosion resistance of A40T coating, but also reduced the penetration and settling of molten salt on the coating.

Applied Materials Today, 2017

Abstract It has been demonstrated for the first time that high-entropy alloys can be synthesised ... more Abstract It has been demonstrated for the first time that high-entropy alloys can be synthesised by electrochemical reduction in a molten salt. This was accomplished by means of an electrolytic cell in which pre-mixed solid metal oxides were subjected to cathodic polarisation in an electrolyte of molten CaCl 2 salt at 1173 K, such that the equiatomic refractory alloys TiNbTaZr and TiNbTaZrHf were produced in a single-step alloying process. Structural investigations revealed that the TiNbTaZr alloy comprises two body-centred cubic phases while the TiNbTaZrHf alloy has one disordered body-centred cubic phase. Further examinations were carried out to assess the alloys’ morphological and mechanical properties. These novel findings promise a straightforward, low-energy and cost-affordable electrometallurgical process for the production of high-entropy alloys for advanced structural applications.

Journal of Thermal Spray Technology, 2015

The thermal cycling behavior of partially stabilized zirconia (PSZ)-coated by plasma-spray proces... more The thermal cycling behavior of partially stabilized zirconia (PSZ)-coated by plasma-spray process on NiCrAlY bond-coated high-density (HD) graphite substrate was investigated. Thermal cycling was carried out at 600 and 750 °C under vacuum, up to 200 cycles. Each cycle comprised a 10-min heating followed by forced air cooling for 10 min down to room temperature. Characterization of the microstructure and the phase analysis of thermal-cycled PSZ coatings by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction (XRD), and Raman spectroscopy revealed the correlation between the microstructural/crystallographic phases and the mechanical integrity of the coating up to 200 cycles. Segmented and vertical cracks generated on the coating during thermal cycling were observed to propagate with increase in the number of cycles. Macrocracks and variations in elemental compositions were not observed until 200 cycles at 600 and 750 °C. XRD and Raman spectroscopic analysis confirmed the presence of nontransformable tetragonal phase only in all the thermal-cycled PSZ coatings, irrespective of temperature up to 200 cycles.

Ceramics International, 2012

... Jagadeesh Sure, A. Ravi Shankar, S. Ramya, U. Kamachi Mudali Corresponding Author Contact Inf... more ... Jagadeesh Sure, A. Ravi Shankar, S. Ramya, U. Kamachi Mudali Corresponding Author Contact Information , E-mail The Corresponding Author. ... and permeability towards oxygen was reduced by thermal spraying of Al 2 O 3 , ZrO 2 with different bond coats (SiC or Cr 3 C 2 ) [20 ...

Surface Review and Letters

Energies

Carbon nanotubes (CNTs) are being increasingly studied as electrode materials for supercapacitors... more Carbon nanotubes (CNTs) are being increasingly studied as electrode materials for supercapacitors (SCs) due to their high electronic conductivity and chemical and mechanical stability. However, their energy density and specific capacitance have not reached the commercial stage due to their electrostatic charge storage system via a non-faradic mechanism. Moreover, magnetite (Fe3O4) exhibits higher specific capacitance originating from its pseudocapacitive behaviour, while it has irreversible volume expansion during cycling. Therefore, a very interesting and facile strategy to arrive at better performance and stability is to integrate CNTs and Fe3O4. In this study, we demonstrate the microwave-solvothermal process for the synthesis of Fe3O4 nanoparticles uniformly grown on a CNT composite as an electrode for SCs. The synthesized Fe3O4/CNT composite delivers a reversible capacitance of 187.1 F/g at 1 A/g, superior rate capability by maintaining 61.6% of 10 A/g (vs. 1 A/g), and cycling ...

Metallurgical and Materials Transactions B, 2021

The study has aimed at understanding the key factors involved in the synthesis of porous Ti-based... more The study has aimed at understanding the key factors involved in the synthesis of porous Ti-based β-Ti-35Nb-7.9Sn alloy by electro-deoxidation of compacted and sintered TiO2-Nb2O5-SnO2 mixed oxide disks in molten calcium chloride. Processing parameters assessed were the sintering temperature, and thus, the open porosity, of the oxide precursor as well as the temperature, voltage, and time of electro-deoxidation. Process conditions were arrived at that enable the complete and efficient reduction of the mixed oxide. The Ti-35Nb-7.9Sn alloy product was single-phase bcc and had a porous microstructure with nodular particles. Electro-deoxidation experiments of different durations allowed the identification of the main intermediate phases occurring during the reduction as well as the mechanism of the oxide-to-alloy conversion. The porous Ti-35Nb-7.9Sn alloy prepared was subjected to corrosion testing in Hanks’ simulated body fluid solution and was found to exhibit superior performance when compared with dense 304L and 316L steels and brass.

Electrochimica Acta, 2021

Lithium-sulfur batteries have shown increasing promise for high energy densities and reduced cost... more Lithium-sulfur batteries have shown increasing promise for high energy densities and reduced costs. Facile sulfur loading techniques demonstrate a critical way to achieving high dispersions of sulfur in the host's matrix, improving conductivity and simultaneously decreasing the active mass loss from the cathode. Here we investigate the effect of sulfur loading methods on the electrochemical performance of porous carbon/sulfur composites containing approximately 70 wt% sulfur. Three different loading techniques are tested, including one-step molten sulfur impregnation (155 °C), two-step molten sulfur impregnation (155 °C + 300 °C) and a sulfur organic solution impregnation, in which the entire microporous volume of carbon is filled by sulfur. It is found that the simple sulfur organic solution impregnation method is the most effective in enhancing the electrochemical performance of the hierarchical porous carbon/sulfur composite cathode in the lithium-sulfur battery system, due to the weaker interaction occurring between the sulfur and microporous carbon. Our work demonstrates the impact of sulfur loading method on the electrochemical performance of lithium-sulfur batteries, which offers new insights into the preparation technology of electrodes.

Materials Today Communications, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Angewandte Chemie, 2020

High-entropy alloys and compounds are becoming an important class of new materials due to their o... more High-entropy alloys and compounds are becoming an important class of new materials due to their outstanding refractory and high-temperature properties. However, preparation in bulk quantities and in powder form via classical metallurgical methods is challenging. Here, we report the first-time synthesis of an ultra-high-temperature highentropy carbide, (TiNbTaZrHf)C, via a facile electrochemical process. In this, a mixture of the individual metal oxides and graphite is deoxidised in a melt of CaCl2 at a temperature of only 1173 K. The (TiNbTaZrHf)C prepared is single-phase fcc and has a powdery morphology with a particle size range of 15-80 nm. Such materials are in demand for modern additive manufacturing techniques while preliminary tests have also indicated a possible application in supercapacitors. The successful synthesis of (TiNbTaZrHf)C powder may now guide the way towards establishing the electrochemical route for the preparation of many other entropy-stabilised materials.

Journal of The Electrochemical Society, 2020

The cost of tantalum (Ta), and thus of Ta capacitors, is undesirably high owing to the limited av... more The cost of tantalum (Ta), and thus of Ta capacitors, is undesirably high owing to the limited availability of its ores and the energy-intensive production. Reported herein is the economically viable electrochemical synthesis of Ta-Nb alloys as a potential replacement for Ta in capacitors. Ta-xNb (x = 20, 50, 80) alloys were prepared directly by electro-deoxidation of Ta2O5-Nb2O5 mixed oxide disks in CaCl2 melt at 900 °C and the results were compared with those for the pure metals. The alloys and metals thus made were in the form of powders and consisted solely of the body-centered cubic phase. The overall compositions of the alloys were close to the target values. EDX and XPS analyses revealed that the particles underwent surface oxidation during the post-electrolytic washing process, thereby forming the required dielectric coating around the metallic cores. Cyclic voltammetry in an aqueous electrolytic cell demonstrated that all powders behaved as typical capacitor materials. TG/D...

Energy Storage Materials, 2019

Solid state electrochemically synthesised β-SiC nanowires as the anode material in lithium ion ba... more Solid state electrochemically synthesised β-SiC nanowires as the anode material in lithium ion batteries Energy Storage Materials,

Journal of The Electrochemical Society, 2018

Silicon carbide was synthesized from mixtures of SiO 2 and graphite by applying the concept of th... more Silicon carbide was synthesized from mixtures of SiO 2 and graphite by applying the concept of the FFC-Cambridge process and several fundamental aspects of the synthesis route were investigated. Porous disks composed of powders of SiO 2 and graphite in molar ratios of 1:0.5, 1:1 and 1:1.5 were prepared by sintering in inert atmosphere and subjected to electro-deoxidation in molten CaCl 2 at 1173 K under a range of experimental conditions. Disks of molar ratio 1:1.5, reduced at an applied voltage of 2.8 V for a duration of 6 h, yielded exclusively phase-pure SiC of nanowire morphology as the reaction product, while the other precursor compositions provided significant amounts of calcium silicides. Voltages lower than 2.8 V gave mixtures of SiC with elemental Si and graphite, and voltages higher than that gave CaSi alone. Shorter electro-deoxidation times led to incomplete reduction and allowed for the identification of CaSiO 3 as a transient phase. Based on the experimental results a multipath reaction mechanism is proposed, consisting of the electrochemical reduction of SiO 2 and CaSiO 3 to Si and the subsequent in-situ carbonization of the Si formed to SiC. The effect of N 2 at high temperature on the electrochemically synthesized SiC was investigated and the formation of nanowire Si 2 N 2 O was observed. Overall, the process presented is a facile single-step and low-temperature method for the synthesis of SiC with possible commercial prospects.

MATERIALS TRANSACTIONS, 2019

TixNbySn alloys with different Nb and Sn contents, of x = 24, 35, 42 mass% and y = 4, 7.9 mass%, ... more TixNbySn alloys with different Nb and Sn contents, of x = 24, 35, 42 mass% and y = 4, 7.9 mass%, were synthesised directly from TiO 2 , Nb 2 O 5 and SnO 2 mixtures via the FFC-Cambridge process. Compacted powder discs were employed as the cathode versus graphite as the anode in molten CaCl 2 as the electrolyte. XRD analysis of the as-synthesised alloys showed that the two alloys with Nb content of 24 mass% were dual-phase ¡/¢-Ti whereas the other four alloys with Nb contents of 35 and 42 mass% were single-phase ¢-Ti. SEM analysis showed that the alloys were highly porous, and that particle size decreased with increase in Nb and Sn contents. Alloy samples of each composition were subjected to short-term and long-term immersion tests in Hanks' simulated body fluid solution. XPS studies then identified a passive oxide film on the surface of the alloy, and a hydroxyapatite layer on top of the oxide. Potentiodynamic polarisation studies revealed excellent corrosion resistance with very small corrosion current densities despite high open porosities. Furthermore, alloy samples were subjected to heat treatment in vacuum. Mechanical testing of these identified a substantial increase of elastic modulus and Vickers hardness. Overall, the experimental programme has brought out that the properties of the TiNbSn alloys prepared are influenced markedly by their Nb and Sn contents, and that single-phase ¢-Ti35Nb4Sn holds promise as a candidate material for body implant applications.

MATERIALS TRANSACTIONS, 2019

Alloy of composition Ti5Ta2Nb (numbers in mass%) was synthesised directly from the corresponding ... more Alloy of composition Ti5Ta2Nb (numbers in mass%) was synthesised directly from the corresponding mixed metal oxides via the FFC-Cambridge process. Compacted powder discs of TiO 2 Ta 2 O 5 Nb 2 O 5 were cathodically polarised against a graphite anode in a molten CaCl 2 electrolyte, and the effect of various process parameters on the synthesis of the alloy was investigated. The samples retained their disc-type shape throughout the oxide-to-metal conversion under appropriate processing conditions. XRD analysis showed that the electrochemically prepared alloy existed as single-phase ¡-Ti and changed into dual-phase (¡+¢)-Ti upon heat treatment. SEM/EDX analysis revealed a nodular porous microstructure and confirmed the intended chemical composition. Backscattered SEM analysis after heat treatment provided direct evidence of micron-sized ¢-phase precipitates at the boundaries of the ¡-phase particles. Microhardness of the heat-treated alloy compared well with literature data for the same material prepared by conventional metallurgical methods. Overall, the study has demonstrated the feasibility of the single-step electrochemical fabrication of Ti5Ta2Nb alloy bodies directly from oxides for structural application.

Journal of Alloys and Compounds, 2019

Single-phase equiatomic CoCrFeNi high-entropy alloy has been synthesised by direct electrochemica... more Single-phase equiatomic CoCrFeNi high-entropy alloy has been synthesised by direct electrochemical reduction from oxide precursors according to the concept of the FFC-Cambridge process. Metal oxide mixtures were heat treated in air to provide a blend of spinels, which were then employed as the cathode in the electro-deoxidation process. Melts of eutectic CaCl 2-NaCl and pure CaCl 2 were used as the electrolytes. Varying the experimental conditions in terms of processing temperature and time yielded CoCrFeNi alloys of diverse morphologies, ranging from fine dispersed powders to solid threedimensional objects, as they are of relevance for additive manufacturing and near-netshape fabrication. Notably, all solid alloy samples exhibited a higher hardness than calculated by the rule of mixture, despite the presence of significant residual porosity. The results highlight the versatility of the FFC-Cambridge process for alloy preparation and suggest the possibility of economically viable large-scale manufacture of steel-type highentropy alloys.

Materials Science and Engineering: C, 2018

Porous titanium-niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by el... more Porous titanium-niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO2 and Nb2O5 powders in molten CaCl2 at 1173 K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase α/β-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase β-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310 K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the bestsuited candidate of the materials studied in regard to biomedical applications.

Transactions of the Indian Institute of Metals, 2016

Plasma sprayed alumina–40 wt% titania (A40T) coatings deposited on high density graphite were las... more Plasma sprayed alumina–40 wt% titania (A40T) coatings deposited on high density graphite were laser melted and immersed in molten LiCl–KCl salt for 24 h at 873 K to compare the corrosion behavior of the coatings before and after laser surface treatment. The as-sprayed and laser melted coatings after exposure to molten salt were characterized to evaluate their microstructure and phase composition. Uniform microstructure and homogeneous surface generated by laser melting process facilitated enhanced protection of the A40T coatings from molten salt attack. Absence of phase change in the coating after corrosion test, implied that no reaction occurred between the molten salt and coating. While keeping other beam parameters constant, increasing the laser average power from 6.4 to 8 W had not only resulted in improving the surface quality and the corrosion resistance of A40T coating, but also reduced the penetration and settling of molten salt on the coating.

Applied Materials Today, 2017

Abstract It has been demonstrated for the first time that high-entropy alloys can be synthesised ... more Abstract It has been demonstrated for the first time that high-entropy alloys can be synthesised by electrochemical reduction in a molten salt. This was accomplished by means of an electrolytic cell in which pre-mixed solid metal oxides were subjected to cathodic polarisation in an electrolyte of molten CaCl 2 salt at 1173 K, such that the equiatomic refractory alloys TiNbTaZr and TiNbTaZrHf were produced in a single-step alloying process. Structural investigations revealed that the TiNbTaZr alloy comprises two body-centred cubic phases while the TiNbTaZrHf alloy has one disordered body-centred cubic phase. Further examinations were carried out to assess the alloys’ morphological and mechanical properties. These novel findings promise a straightforward, low-energy and cost-affordable electrometallurgical process for the production of high-entropy alloys for advanced structural applications.

Journal of Thermal Spray Technology, 2015

The thermal cycling behavior of partially stabilized zirconia (PSZ)-coated by plasma-spray proces... more The thermal cycling behavior of partially stabilized zirconia (PSZ)-coated by plasma-spray process on NiCrAlY bond-coated high-density (HD) graphite substrate was investigated. Thermal cycling was carried out at 600 and 750 °C under vacuum, up to 200 cycles. Each cycle comprised a 10-min heating followed by forced air cooling for 10 min down to room temperature. Characterization of the microstructure and the phase analysis of thermal-cycled PSZ coatings by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction (XRD), and Raman spectroscopy revealed the correlation between the microstructural/crystallographic phases and the mechanical integrity of the coating up to 200 cycles. Segmented and vertical cracks generated on the coating during thermal cycling were observed to propagate with increase in the number of cycles. Macrocracks and variations in elemental compositions were not observed until 200 cycles at 600 and 750 °C. XRD and Raman spectroscopic analysis confirmed the presence of nontransformable tetragonal phase only in all the thermal-cycled PSZ coatings, irrespective of temperature up to 200 cycles.