The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting s... more The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting size and shape of nanocrystalline (NC) silver is presented. It is shown that all the NC silver samples investigated, in this study, have displayed face centered cubic structure. The average coherently scattering domain size is estimated with the help of Scherrer equation. Having computed this, an attempt has been made to understand the UV-Vis spectra of the NC sols in terms of localized surface plasmon resonance (LSPR) behaviour. The change in the nature of LSPR in visible range of spectrum of the sols has been attributed to the complex interplay of shape, size and distribution of NC silver. The chemical reduction synthesis route 1-3 has been employed for producing NC phase of noble metals. The NC particles of these metals have lot of potentials for bio-medical applications 4 . Apart from these, their sols offer very good opportunity to understand the (localized surface plasmon resonance)...
The fracture toughness of a hot pressed ZrB2-20 vol.% MoSi2 based ultra high temperature ceramic ... more The fracture toughness of a hot pressed ZrB2-20 vol.% MoSi2 based ultra high temperature ceramic composite was measured by the Vickers indentation method and single edge notch bend test (SENB). The material was tested for indentation fracture toughness (IFT) at room temperature at four different loads between 49.03 and 196.3 N and four different indentation times between 15 and 30 s. Different formulae that exist to evaluate IFT were compared. The influences of the indentation load and the dwell time on IFT measurement were investigated. Results confirmed that the transformation occur from Palmqvist crack system to median crack system between low load to higher loads. The Palmqvist crack model yielded an IFT of ~3 MPa√m, whereas, the median crack model yielded an IFT of ~3–4 MPa√m. It is seen that the use of actual crack system at a particular test load gives almost similar fracture toughness values which are measured by the standard conventional method.
While descending through different layers of atmosphere with tremendously high velocities, hypers... more While descending through different layers of atmosphere with tremendously high velocities, hypersonic re-entry nosecones fabricated using ultra-high temperature ceramic matrix composites (UHTCMCs) are subjected to repeated thermal shocks. This necessitates extensive investigations on the cyclic oxidation behaviour of UHTCMCs at temperatures ranging from 1100°C to 1300°C (service temperature of the nosecones). To this end, the present work is aimed at investigating the cyclic oxidation behaviour of ZrB2 -20 vol.%MoSi2 (ZM20) UHTCMC (a very widely investigated ZM CMC) by carrying out cycles for 6h, at 1cycle/h and estimating oxidation kinetic law. This has been followed by extensive characterisation using X-Ray Diffraction (XRD) to indicate the phases formed during oxidation and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), in order to determine the chemical composition of the oxides formed between 1100°C and 1300°C.
At present, fabrication of ceramics using AM-based techniques mainly suffers from two primary lim... more At present, fabrication of ceramics using AM-based techniques mainly suffers from two primary limitations, viz: (i) low density and (ii) poor mechanical properties of the finished components. It is worth mentioning that the present state of research in the avenue of AM-based ceramics is focussed mainly on fabricating ceramic and cermet components with enhanced densities and improved mechanical properties. However, to the best of the authors’ knowledge, not much is known about the microstructure evolution and its correlation with the mechanical properties of the finished parts. Addressing the aforementioned avenue is highly essential for understanding the utilisation of these components for structural applications. To this end, the present review article is aimed to address the future perspectives in this avenue has been provided with a special emphasis on the need to establish a systematic structure-property correlation in these materials.
The last two decades have witnessed a large volume of research revolving around structure-propert... more The last two decades have witnessed a large volume of research revolving around structure-property correlation in carbon-based nanocomposites, synthesized by several methods. In the simplest of terms, the electronic properties of these nanomaterials, which form the present context of discussion, vary mainly as a function of three parameters, out of which two are process parameters (viz. (i) the kind of reinforcement and (ii) method of synthesis), and one is a structure-dependent parameter. The structure-dependent parameter is highly influenced by the two process parameters and plays a vital role in determining the ionic and electronic transport phenomenon in these materials. In other words, the interaction between electrons and the equilibrium 0-D (point) defects, along with different types of 2-D interfaces, plays a crucial role in the understanding of electronic properties, apart from physical and chemical properties of these materials. The present chapter provides a brief overvie...
The present decade has witnessed a huge volume of research revolving around a number of Additive ... more The present decade has witnessed a huge volume of research revolving around a number of Additive Manufacturing (AM) techniques, especially for the fabrication of different metallic materials. However, fabrication of ceramics and cermets using AM-based techniques mainly suffers from two primary limitations which are: (i) low density and (ii) poor mechanical properties of the final components. Although there has been a considerable volume of work on AM based techniques for manufacturing ceramic and cermet parts with enhanced densities and improved mechanical properties, however, there is limited understanding on the correlation of microstructure of AM-based ceramic and cermet components with the mechanical properties. The present article is aimed to review some of the most commonly used AM techniques for the fabrication of ceramics and cermets. This has been followed by a brief discussion on the microstructural developments during different AM-based techniques. In addition, an overvie...
In this study, aluminum-based metal matrix composites containing 5, 10, 15, 20, and 25% fly ash p... more In this study, aluminum-based metal matrix composites containing 5, 10, 15, 20, and 25% fly ash particles by weight have been fabricated using a stir casting route. Microstructural observations under an optical microscope suggest that fly ash particles in the cast composites are uniformly distributed throughout the matrix. The mechanical properties such as tensile strength and hardness of the aluminum alloy have enhanced significantly with the addition of fly ash. Wear behavior of base metal and its composite have been studied in dry sliding conditions using a pin-on-disc tribometer. Wear tests have been conducted at three different loads of 9.81, 19.62, and 29.43 N at a constant sliding velocity of 1.3 m s −1. Microstructural observations of worn surfaces and wear debris suggest that wear mechanism in base metal is controlled by adhesion, whereas that for composites is abrasive. The least wear rate has been obtained in Al-10% Fly ash composite. The Al-10% Fly ash is observed to possess an optimum level of mechanical properties and wear behavior.
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019
In this investigation, the hypereutectic in-situ Al-X wt. %M g 2 Si (X=15, 20, 25 and 30) composi... more In this investigation, the hypereutectic in-situ Al-X wt. %M g 2 Si (X=15, 20, 25 and 30) composites have been developed through gravity casting technique with the use of commercially pure Al, Si and M g metals. This composite comprises of three phases, namely the primary M g 2 Si phase, which is formed during the pseudo-eutectic transformation at the time of solidification engulfed by the matrix (α-Al) and the binary eutectic (Al-Mg 2 Si) phase. M icrostructure evaluation and the mechanical properties of these composites has been investigated. It is observed that the change M g 2 Si concentration has a great impression not only on the morphology and volume fraction but also in the hardness of all the phases that exist. The size and volume percentage of M g 2 Si particle increases with the increase in M g 2 Si concentration. Bulk hardness also increases with higher M g 2 Si concentration. The micro hardness of the reinforcement (primary Mg 2 Si) particle decreased slightly with the increase in the M g 2 Si concentration due to the less compact particle. On the contrary, the micro hardness of the other phases showed a gradual rise with the rise in M g 2 Si concentration. The higher values of Quality Index, % elongation, ultimate tensile strength and toughness are achieved in the samples where the M g 2 Si concentration is nearer to the pseudo-eutectic (13.9 wt. %) region. The yield strength, firstly shows a rising trend up to 25 wt. % M g 2 Si and then decreases at 30 wt. % M g 2 Si concentration.
The oxidation behavior of ZrB 2-20 vol % SiC and ZrB 2-20 vol % SiC-5 vol % Si 3 N 4 composites p... more The oxidation behavior of ZrB 2-20 vol % SiC and ZrB 2-20 vol % SiC-5 vol % Si 3 N 4 composites prepared by hot-pressing and subjected to isothermal exposure at 1200 or 1300 • C for durations of 24 or 100 h in air, as well as cyclic exposure at 1300 • C for 24 h, have been investigated. The oxidation resistance of the ZrB 2-20 vol % SiC composite has been found to improve by around 20%-25% with addition of 5 vol % Si 3 N 4 during isothermal or cyclic exposures at 1200 or 1300 • C. This improvement in oxidation resistance has been attributed to the formation of higher amounts of SiO 2 and Si 2 N 2 O, as well as a greater amount of continuity in the oxide scale, because these phases assist in closing the pores and lower the severity of cracking by exhibiting self-healing type behavior. For both the composites, the mass changes are found to be higher during cyclic exposure at 1300 • C by about 2 times compared to that under isothermal conditions.
The fracture toughness of a hot pressed ZrB 2-20 vol.% MoSi 2 based ultra high temperature cerami... more The fracture toughness of a hot pressed ZrB 2-20 vol.% MoSi 2 based ultra high temperature ceramic composite was measured by the Vickers indentation method and single edge notch bend test (SENB). The material was tested for indentation fracture toughness (IFT) at room temperature at four different loads between 49.03 and 196.3 N and four different indentation times between 15 and 30 s. Different formulae that exist to evaluate IFT were compared. The influences of the indentation load and the dwell time on IFT measurement were investigated. Results confirmed that the transformation occur from Palmqvist crack system to median crack system between low load to higher loads. The Palmqvist crack model yielded an IFT of ~3 MPa√m, whereas, the median crack model yielded an IFT of ~3-4 MPa√m. It is seen that the use of actual crack system at a particular test load gives almost similar fracture toughness values which are measured by the standard conventional method.
ABSTRACT The dendritic structure in a cast Cu-12.6 wt pct Sn alloy can be transformed to a globul... more ABSTRACT The dendritic structure in a cast Cu-12.6 wt pct Sn alloy can be transformed to a globular structure if the alloy is heat treated in the semisolid range. A Cu-12.6 wt pct Sn alloy has a wide solidification range which encourages the development of a cored dendritic structure during solidification. In order to transform it into a globular structure, heat treatment was carried out separately at three temperatures in the semisolid range, namely 1183 K, 1153 K, and 1123 K (910 °C, 880 °C, and 850 °C) with corresponding liquid volume fractions of 50, 40, and 20 pct, respectively. An attempt was made to optimize the temperature and vol pct of liquid combination. It was observed that microstructural modification proceeded mainly through coarsening, fragmentation, and spheroidization of the dendrite arms. Semisolid heat treatment at 1123 K (850 °C) for 2 hours with 20 vol pct liquid yielded the best result. This microstructure was compared with the microstructure developed by solid-state heat treatment at 1023 K (750 °C) for 2 hours. Assessment of the structure-property co-relation demonstrated that hardness, yield stress, ultimate tensile stress, and toughness of the semisolid heat-treated samples were superior to those of subcritically annealed samples.
ABSTRACT Compressive creep studies have been carried out on hot-pressed ZrB2–SiC (ZS) and ZrB2–Si... more ABSTRACT Compressive creep studies have been carried out on hot-pressed ZrB2–SiC (ZS) and ZrB2–SiC–Si3N4 (ZSS) composites in air under stress and temperature ranges of 93–140 MPa and 1300°C–1425°C, respectively for time durations of ≈20–40 h. The results of these studies have shown the creep resistance of ZS composite to be greater than that of ZSS. As the temperature is increased from 1300°C to 1425°C, the stress exponent of ZS decreases from 1.7 to 1.1, whereas that of ZSS drops from 1.6 to 0.6. The activation energies for these composites have been found as ≈95 ± 32 kJ/mol at temperatures ≤1350°C, and as ≈470 ± 20 kJ/mol in the range of 1350°C–1425°C. Studies of the postcreep microstructures using scanning and transmission electron microscopy have shown the presence of glassy film with cracks at both ZrB2 grain boundaries and ZrB2–SiC interfaces. These results along with calculated values of activation volumes suggest grain-boundary sliding as the major damage mechanism, which is controlled by O2− diffusion through SiO2 at ≤1350°C, and by viscoplastic flow of the glassy interfacial film at temperatures ≥1350°C. Studies by transmission electron microscopy have shown formation of crystalline precipitates of Si2N2O near ZrB2–SiC interfaces in ZSS tested at ≥1400°C, which along with stress exponent values <1 suggests that grain-boundary sliding involving solution-precipitation-type mechanism is operative at these temperatures.
The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting s... more The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting size and shape of nanocrystalline (NC) silver is presented. It is shown that all the NC silver samples investigated, in this study, have displayed face centered cubic structure. The average coherently scattering domain size is estimated with the help of Scherrer equation. Having computed this, an attempt has been made to understand the UV-Vis spectra of the NC sols in terms of localized surface plasmon resonance (LSPR) behaviour. The change in the nature of LSPR in visible range of spectrum of the sols has been attributed to the complex interplay of shape, size and distribution of NC silver. The chemical reduction synthesis route 1-3 has been employed for producing NC phase of noble metals. The NC particles of these metals have lot of potentials for bio-medical applications 4 . Apart from these, their sols offer very good opportunity to understand the (localized surface plasmon resonance)...
The fracture toughness of a hot pressed ZrB2-20 vol.% MoSi2 based ultra high temperature ceramic ... more The fracture toughness of a hot pressed ZrB2-20 vol.% MoSi2 based ultra high temperature ceramic composite was measured by the Vickers indentation method and single edge notch bend test (SENB). The material was tested for indentation fracture toughness (IFT) at room temperature at four different loads between 49.03 and 196.3 N and four different indentation times between 15 and 30 s. Different formulae that exist to evaluate IFT were compared. The influences of the indentation load and the dwell time on IFT measurement were investigated. Results confirmed that the transformation occur from Palmqvist crack system to median crack system between low load to higher loads. The Palmqvist crack model yielded an IFT of ~3 MPa√m, whereas, the median crack model yielded an IFT of ~3–4 MPa√m. It is seen that the use of actual crack system at a particular test load gives almost similar fracture toughness values which are measured by the standard conventional method.
While descending through different layers of atmosphere with tremendously high velocities, hypers... more While descending through different layers of atmosphere with tremendously high velocities, hypersonic re-entry nosecones fabricated using ultra-high temperature ceramic matrix composites (UHTCMCs) are subjected to repeated thermal shocks. This necessitates extensive investigations on the cyclic oxidation behaviour of UHTCMCs at temperatures ranging from 1100°C to 1300°C (service temperature of the nosecones). To this end, the present work is aimed at investigating the cyclic oxidation behaviour of ZrB2 -20 vol.%MoSi2 (ZM20) UHTCMC (a very widely investigated ZM CMC) by carrying out cycles for 6h, at 1cycle/h and estimating oxidation kinetic law. This has been followed by extensive characterisation using X-Ray Diffraction (XRD) to indicate the phases formed during oxidation and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), in order to determine the chemical composition of the oxides formed between 1100°C and 1300°C.
At present, fabrication of ceramics using AM-based techniques mainly suffers from two primary lim... more At present, fabrication of ceramics using AM-based techniques mainly suffers from two primary limitations, viz: (i) low density and (ii) poor mechanical properties of the finished components. It is worth mentioning that the present state of research in the avenue of AM-based ceramics is focussed mainly on fabricating ceramic and cermet components with enhanced densities and improved mechanical properties. However, to the best of the authors’ knowledge, not much is known about the microstructure evolution and its correlation with the mechanical properties of the finished parts. Addressing the aforementioned avenue is highly essential for understanding the utilisation of these components for structural applications. To this end, the present review article is aimed to address the future perspectives in this avenue has been provided with a special emphasis on the need to establish a systematic structure-property correlation in these materials.
The last two decades have witnessed a large volume of research revolving around structure-propert... more The last two decades have witnessed a large volume of research revolving around structure-property correlation in carbon-based nanocomposites, synthesized by several methods. In the simplest of terms, the electronic properties of these nanomaterials, which form the present context of discussion, vary mainly as a function of three parameters, out of which two are process parameters (viz. (i) the kind of reinforcement and (ii) method of synthesis), and one is a structure-dependent parameter. The structure-dependent parameter is highly influenced by the two process parameters and plays a vital role in determining the ionic and electronic transport phenomenon in these materials. In other words, the interaction between electrons and the equilibrium 0-D (point) defects, along with different types of 2-D interfaces, plays a crucial role in the understanding of electronic properties, apart from physical and chemical properties of these materials. The present chapter provides a brief overvie...
The present decade has witnessed a huge volume of research revolving around a number of Additive ... more The present decade has witnessed a huge volume of research revolving around a number of Additive Manufacturing (AM) techniques, especially for the fabrication of different metallic materials. However, fabrication of ceramics and cermets using AM-based techniques mainly suffers from two primary limitations which are: (i) low density and (ii) poor mechanical properties of the final components. Although there has been a considerable volume of work on AM based techniques for manufacturing ceramic and cermet parts with enhanced densities and improved mechanical properties, however, there is limited understanding on the correlation of microstructure of AM-based ceramic and cermet components with the mechanical properties. The present article is aimed to review some of the most commonly used AM techniques for the fabrication of ceramics and cermets. This has been followed by a brief discussion on the microstructural developments during different AM-based techniques. In addition, an overvie...
In this study, aluminum-based metal matrix composites containing 5, 10, 15, 20, and 25% fly ash p... more In this study, aluminum-based metal matrix composites containing 5, 10, 15, 20, and 25% fly ash particles by weight have been fabricated using a stir casting route. Microstructural observations under an optical microscope suggest that fly ash particles in the cast composites are uniformly distributed throughout the matrix. The mechanical properties such as tensile strength and hardness of the aluminum alloy have enhanced significantly with the addition of fly ash. Wear behavior of base metal and its composite have been studied in dry sliding conditions using a pin-on-disc tribometer. Wear tests have been conducted at three different loads of 9.81, 19.62, and 29.43 N at a constant sliding velocity of 1.3 m s −1. Microstructural observations of worn surfaces and wear debris suggest that wear mechanism in base metal is controlled by adhesion, whereas that for composites is abrasive. The least wear rate has been obtained in Al-10% Fly ash composite. The Al-10% Fly ash is observed to possess an optimum level of mechanical properties and wear behavior.
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019
In this investigation, the hypereutectic in-situ Al-X wt. %M g 2 Si (X=15, 20, 25 and 30) composi... more In this investigation, the hypereutectic in-situ Al-X wt. %M g 2 Si (X=15, 20, 25 and 30) composites have been developed through gravity casting technique with the use of commercially pure Al, Si and M g metals. This composite comprises of three phases, namely the primary M g 2 Si phase, which is formed during the pseudo-eutectic transformation at the time of solidification engulfed by the matrix (α-Al) and the binary eutectic (Al-Mg 2 Si) phase. M icrostructure evaluation and the mechanical properties of these composites has been investigated. It is observed that the change M g 2 Si concentration has a great impression not only on the morphology and volume fraction but also in the hardness of all the phases that exist. The size and volume percentage of M g 2 Si particle increases with the increase in M g 2 Si concentration. Bulk hardness also increases with higher M g 2 Si concentration. The micro hardness of the reinforcement (primary Mg 2 Si) particle decreased slightly with the increase in the M g 2 Si concentration due to the less compact particle. On the contrary, the micro hardness of the other phases showed a gradual rise with the rise in M g 2 Si concentration. The higher values of Quality Index, % elongation, ultimate tensile strength and toughness are achieved in the samples where the M g 2 Si concentration is nearer to the pseudo-eutectic (13.9 wt. %) region. The yield strength, firstly shows a rising trend up to 25 wt. % M g 2 Si and then decreases at 30 wt. % M g 2 Si concentration.
The oxidation behavior of ZrB 2-20 vol % SiC and ZrB 2-20 vol % SiC-5 vol % Si 3 N 4 composites p... more The oxidation behavior of ZrB 2-20 vol % SiC and ZrB 2-20 vol % SiC-5 vol % Si 3 N 4 composites prepared by hot-pressing and subjected to isothermal exposure at 1200 or 1300 • C for durations of 24 or 100 h in air, as well as cyclic exposure at 1300 • C for 24 h, have been investigated. The oxidation resistance of the ZrB 2-20 vol % SiC composite has been found to improve by around 20%-25% with addition of 5 vol % Si 3 N 4 during isothermal or cyclic exposures at 1200 or 1300 • C. This improvement in oxidation resistance has been attributed to the formation of higher amounts of SiO 2 and Si 2 N 2 O, as well as a greater amount of continuity in the oxide scale, because these phases assist in closing the pores and lower the severity of cracking by exhibiting self-healing type behavior. For both the composites, the mass changes are found to be higher during cyclic exposure at 1300 • C by about 2 times compared to that under isothermal conditions.
The fracture toughness of a hot pressed ZrB 2-20 vol.% MoSi 2 based ultra high temperature cerami... more The fracture toughness of a hot pressed ZrB 2-20 vol.% MoSi 2 based ultra high temperature ceramic composite was measured by the Vickers indentation method and single edge notch bend test (SENB). The material was tested for indentation fracture toughness (IFT) at room temperature at four different loads between 49.03 and 196.3 N and four different indentation times between 15 and 30 s. Different formulae that exist to evaluate IFT were compared. The influences of the indentation load and the dwell time on IFT measurement were investigated. Results confirmed that the transformation occur from Palmqvist crack system to median crack system between low load to higher loads. The Palmqvist crack model yielded an IFT of ~3 MPa√m, whereas, the median crack model yielded an IFT of ~3-4 MPa√m. It is seen that the use of actual crack system at a particular test load gives almost similar fracture toughness values which are measured by the standard conventional method.
ABSTRACT The dendritic structure in a cast Cu-12.6 wt pct Sn alloy can be transformed to a globul... more ABSTRACT The dendritic structure in a cast Cu-12.6 wt pct Sn alloy can be transformed to a globular structure if the alloy is heat treated in the semisolid range. A Cu-12.6 wt pct Sn alloy has a wide solidification range which encourages the development of a cored dendritic structure during solidification. In order to transform it into a globular structure, heat treatment was carried out separately at three temperatures in the semisolid range, namely 1183 K, 1153 K, and 1123 K (910 °C, 880 °C, and 850 °C) with corresponding liquid volume fractions of 50, 40, and 20 pct, respectively. An attempt was made to optimize the temperature and vol pct of liquid combination. It was observed that microstructural modification proceeded mainly through coarsening, fragmentation, and spheroidization of the dendrite arms. Semisolid heat treatment at 1123 K (850 °C) for 2 hours with 20 vol pct liquid yielded the best result. This microstructure was compared with the microstructure developed by solid-state heat treatment at 1023 K (750 °C) for 2 hours. Assessment of the structure-property co-relation demonstrated that hardness, yield stress, ultimate tensile stress, and toughness of the semisolid heat-treated samples were superior to those of subcritically annealed samples.
ABSTRACT Compressive creep studies have been carried out on hot-pressed ZrB2–SiC (ZS) and ZrB2–Si... more ABSTRACT Compressive creep studies have been carried out on hot-pressed ZrB2–SiC (ZS) and ZrB2–SiC–Si3N4 (ZSS) composites in air under stress and temperature ranges of 93–140 MPa and 1300°C–1425°C, respectively for time durations of ≈20–40 h. The results of these studies have shown the creep resistance of ZS composite to be greater than that of ZSS. As the temperature is increased from 1300°C to 1425°C, the stress exponent of ZS decreases from 1.7 to 1.1, whereas that of ZSS drops from 1.6 to 0.6. The activation energies for these composites have been found as ≈95 ± 32 kJ/mol at temperatures ≤1350°C, and as ≈470 ± 20 kJ/mol in the range of 1350°C–1425°C. Studies of the postcreep microstructures using scanning and transmission electron microscopy have shown the presence of glassy film with cracks at both ZrB2 grain boundaries and ZrB2–SiC interfaces. These results along with calculated values of activation volumes suggest grain-boundary sliding as the major damage mechanism, which is controlled by O2− diffusion through SiO2 at ≤1350°C, and by viscoplastic flow of the glassy interfacial film at temperatures ≥1350°C. Studies by transmission electron microscopy have shown formation of crystalline precipitates of Si2N2O near ZrB2–SiC interfaces in ZSS tested at ≥1400°C, which along with stress exponent values <1 suggests that grain-boundary sliding involving solution-precipitation-type mechanism is operative at these temperatures.
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Papers by Manab Mallik