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Papers by Kamanio CHATTOPADHYAY

Research paper thumbnail of The ω Phase Formation during Laser Cladding and Remelting of Quasicrystal Forming AlCuFe on Pure Aluminum

MRS Proceedings, 2003

ABSTRACTWe report the formation ω phase in the remelted layers during laser cladding and remeltin... more ABSTRACTWe report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω ...

Research paper thumbnail of Continuous welding of Cu–Ni dissimilar couple using CO 2 laser

Science and Technology of Welding and Joining, 2005

The evolution of microstructure during continuous laser welding of dissimilar metals has been stu... more The evolution of microstructure during continuous laser welding of dissimilar metals has been studied for a binary Cu-Ni couple. The effects of laser beam scan speed and laser power on the shape and size of the melt pool, the weldment-substrate interface, the composition profiles, and microstructures of the weldments have been investigated. It is shown that the melt pools exhibit a characteristic asymmetry in shape. The observed microstructure is characterised by the existence of compositional and microstructural variations leading to a banded appearance suggesting localised mixing. Distinct differences exist in the evolution of the microstructure in the copper and nickel sides of the weld pool. An attempt is made to explain some of the experimental observations using thermodynamic and thermal transport arguments.

Research paper thumbnail of Solidification microstructure development

Sadhana, 2001

In the present article, evolution of microstructure during solidification, as a function of vario... more In the present article, evolution of microstructure during solidification, as a function of various parameters, is discussed. Macrosegregation is described as being due to insufficient diffusivity of solute in the solid. Pattern formation is discussed in the light of instabilities at the solidification growth front. An overview of the scaling relations for various microstructures is given. Metastable extensions to equilibrium phase diagrams and corrections to equilibrium quantities are described.

Research paper thumbnail of Characterization of a continuous CO2 laser-welded Fe-Cu dissimilar couple

Metallurgical and Materials Transactions A, 2005

Continuous CO 2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different ... more Continuous CO 2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different process conditions is studied. The process conditions are varied to identify and characterize the microstructural features that are independent of the welding mode. The study presents a characterization of the microstructure and mechanical properties of the welds. Detailed microstructural analysis of the weld/base-metal interface shows features that are different on the two sides of the weld. The iron side can grow into the weld with a local change in length scale, whereas the interface on the copper side indicates a barrier to growth. The interface is jagged, and a banded microstructure consisting of iron-rich layers could be observed next to the weld/Cu interface. The observations suggest that solidification initiates inside the melt, where iron and copper are mixed due to convective flow. The transmission electron microscopy (TEM) of the weld region also indicates the occasional presence of droplets of iron and copper. The microstructural observations are rationalized using arguments drawn from a thermodynamic analysis of the Fe-Cu system.

Research paper thumbnail of Microstructural evolution during remelting of laser surface alloyed hyper-monotectic Al–Bi alloy

Materials Science and Engineering: A, 2004

The present investigation explores the possibility of synthesizing a two-phase microstructure con... more The present investigation explores the possibility of synthesizing a two-phase microstructure consisting of a fine dispersion of bismuth particles in an aluminium matrix using the laser surface alloying technique. The possibility of controlling the size distribution of bismuth particles by subsequent remelting is also investigated. The microstructural analysis of the surface alloyed samples shows that the average size of the bismuth particles reduces with increase in laser scan speed. In order to understand the factors that determine the nature of the size distribution of the particles, a detailed model is developed. The model incorporates heat and fluid flow induced by the laser to arrive at the evolution of the temperature and velocity of the melt in three dimensions. Using these as inputs, a kinetic analysis of the nucleation, growth and coarsening induced by collision-controlled coalescence of the bismuth particles from the melt is carried out. Comparison with the experiments indicates that coalescence due to convection plays an important role in the evolution of the size distribution of bismuth particles.

Research paper thumbnail of Microstructure evolution in laser alloyed layer of Cu–Fe–Al–Si on Cu substrate

Materials Science and Engineering: A, 2004

Laser alloyed layers of Cu-Fe-Al-Si were prepared using an 8 kW CO 2 laser on copper substrate an... more Laser alloyed layers of Cu-Fe-Al-Si were prepared using an 8 kW CO 2 laser on copper substrate and a detailed TEM investigation of the cross-section microstructure was carried out. This paper elucidates on the sequence of evolution of various phases constituting a complex microstructure due to non-equilibrium solidification of the laser alloyed layer. The formation of micron size Fe-rich globules having DO 3 structure within Cu-rich fcc matrix suggests access to a submerged miscibility gap during the laser processing. The solute rejection processes during later stages of solidification and solid state cooling result in the evolution of submicron size Cu-rich dispersoids inside the Fe-rich globules and the Fe-rich nanoscale fully coherent precipitates within the surrounding Cu-rich matrix.

Research paper thumbnail of Non-equilibrium solidification of concentrated Fe–Ge alloys

Materials Science and Engineering: A, 2007

Research paper thumbnail of Laser cladding of quasicrystal forming Al–Cu–Fe on aluminum

Journal of Non-Crystalline Solids, 2004

Composite quasicrystalline coatings are developed by laser cladding of an elemental powder mixtur... more Composite quasicrystalline coatings are developed by laser cladding of an elemental powder mixture of aluminum, copper and iron on an aluminum substrate. Some of the tracks are remelted to see the effect of phase formation and related changes in hardness during remelting. The clad layers start growing with a cellular morphology from the substrate. The icosahedral phase forms in all the tracks along with some aluminides. It has also been found that the icosahedral phase forms both by a peritectic reaction between the liquid and Al 13 Fe 4 and by direct nucleation from the liquid. This is a clear indication of a different levels of undercooling that the liquid undergoes before the nucleation of the primary phase inside the clad layers during laser processing. The formation of Al 13 Fe 4 with a ten-pointed star like morphology has also been found at the bottom of the clad. The remelting of the clad tracks leads to a change in microstructure as far as phase formation is concerned. The formation of long lath-shaped Al 13 Fe 4 can be observed in the remelted layer. The hardness profiles of the clad and remelted layers reveal a hardness (HV 0:025) around 600.

Research paper thumbnail of Densification and microstructure development in spark plasma sintered WC–6 wt% ZrO2 nanocomposites

Journal of Materials Research, 2007

In this paper, we report the results of a transmission electron microscopy investigation on WC–6 ... more In this paper, we report the results of a transmission electron microscopy investigation on WC–6 wt% ZrO2nanocomposite, spark plasma sintered at 1300 °C, for varying times of up to 20 min. The primary aim of this work was to understand the evolution of microstructure during such a sintering process. The investigation revealed the presence of nanocrystalline ZrO2particles (30–50 nm) entrapped within submicron WC grains. In addition, relatively coarser ZrO2(60–100 nm) particles were observed to be either attached to WC grain boundaries or located at WC triple grain junctions. The evidence of the presence of a small amount of W2C, supposed to have been formed due to sintering reaction between WC and ZrO2, is presented here. Detailed structural investigation indicated that ZrO2in the spark plasma sintered nanocomposite adopted an orthorhombic crystal structure, and the possible reasons for o-ZrO2formation are explained. The increase in kinetics of densification due to the addition of Zr...

Research paper thumbnail of Microstructural evolution in laser-ablation-deposited Fe–25 at.% Ge thin film

Journal of Materials Research, 2006

Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single cry... more Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single crystal NaCl and Cu substrates at room temperature. Both the vapor and liquid droplets generated in this process are quenched on the substrate. The microstructures of the embedded droplets show size as well as composition dependence. The hierarchy of phase evolution from amorphous to body-centered cubic (bcc) to DO3 has been observed as a function of size. Some of the medium-sized droplets also show direct formation of ordered DO19 phase from the starting liquid. The evolution of disordered bcc structure in some of the droplets indicates disorder trapping during liquid to solid transformation. The microstructural evolution is analyzed on the basis of heat transfer mechanisms and continuous growth model in the solidifying droplets.

Research paper thumbnail of Melting and superheating of metals and alloys

Progress in Materials Science, 1997

Research paper thumbnail of Depression of melting point of multidomained bismuth in aluminum based metallic glass nanocomposites

Applied Physics Letters, 1996

Research paper thumbnail of Melting of Bi nanoparticles embedded in a Zn matrix

Acta Materialia, 2004

We report the melting behavior of nanometric-Bi particles embedded in the zinc matrix synthesized... more We report the melting behavior of nanometric-Bi particles embedded in the zinc matrix synthesized by the rapid solidification processing. These particles have specific orientation relation with the matrix given by {0 0 0 1} Zn i{1 0-1 2} Bi and AE1 1-2 0ae Zn nearly iAE1-2 1 0ae Bi. A change in melting behavior is observed on thermal cycling. The differential scanning calorimetry (DSC) results reveal that a fraction of Bi particles melts at 91-95 K below the bulk melting temperature during the second DSC-cycle. It is shown that the division of a single crystalline nano-Bi particle into several grains during solidification results in the significant reduction in melting, which can be explained by the phenomenological theory of melting.

Research paper thumbnail of Solidification of undercooled peritectic Fe–Ge alloy

Acta Materialia, 2005

Bulk samples of Fe-25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic ... more Bulk samples of Fe-25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic levitation technique. The growth rate of the primary phase is measured using a capacitance proximity sensor technique. Solidification microstructure is studied as a function of undercooling. The microstructure of samples at low undercoolings consists of a residual primary phase a 2 , peritectic phase e and inter-dendritic e-b eutectic. Microstructure at higher undercoolings is nearly phase-pure e. Time resolved diffraction analysis of the levitated droplets using synchrotron radiation indicates the nucleation of primary a 2 in all cases. The growth rate is analysed using current theories to explain the experimental observations. Interfacial undercooling is found to play an important role in the growth kinetics. Our results also suggest suppression of peritectic reaction.

Research paper thumbnail of The Role of Interfaces in Diffusional Growth

Research paper thumbnail of Behaviour of Embedded Metals and Alloys at Small Sizes

Research paper thumbnail of Morphogenesis and mechanostabilization of complex natural and 3D printed shapes

Science Advances, 2015

The natural selection and the evolutionary optimization of complex shapes in nature are closely r... more The natural selection and the evolutionary optimization of complex shapes in nature are closely related to their functions. Mechanostabilization of shape of biological structure via morphogenesis has several beautiful examples. With the help of simple mechanics-based modeling and experiments, we show an important causality between natural shape selection as evolutionary outcome and the mechanostabilization of seashells. The effect of biological growth on the mechanostabilization process is identified with examples of two natural shapes of seashells, one having a diametrically converging localization of stresses and the other having a helicoidally concentric localization of stresses. We demonstrate how the evolved shape enables predictable protection of soft body parts of the species. The effect of bioavailability of natural material is found to be a secondary factor compared to shape selectivity, where material microstructure only acts as a constraint to evolutionary optimization. T...

Research paper thumbnail of Hardness behaviour of ultrafine dispersed materials with soft dispersoids: The case of rapidly solidified Zn-Bi immiscible alloy

Scripta Metallurgica et Materialia, 1993

ABSTRACT

Research paper thumbnail of An electron microscopic study of quasicrystals in a quaternary alloy : Mg32(Al, Zn, Cu)49

Scripta Metallurgica, 1986

The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapi... more The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapidly solidified Al-14at%Mn alloy has activated intensive studies of a new class of solids, termed as quasicrystals (2). While the original discovery reported the existence of quasicrystals in AI-Mn. AI-Fe and AI-Cr alloys, subsequent work has revealed their existence in Mg-Zn-Al(3,4), Mg-A]-Cu(5), AI-Mn-Si(6) and Ti-Ni-V(7) alloys (Table l). We had earlier reported on the variety of electron diffraction patterns from quasicrystals h~ AI-Mn alloys (g-10). Ramachandrarao and Sastry (3) had argued the existence of quasicrystals in Mg-Zn-AI and Mg-AI-Cu alloys on the basis of the prevalence of icosahedrai coordination in crystalline Mg32(AI, Zn)49 structure~ as was demonstrated by Bergman et. al. (ll). The quaternary system Mg-AI-Zn-C~ had been investigated much earlier by Strawbridge et. al. (12). Fig. 1 gives from their classical work the domain of existence of the crystalline T-phase in the quaternary system Mg-AI-Zn-Cu. We felt that this quaternary alloy should also give rise to quasicrystals with additional stability endowed by the addition of Cu. A comparison of electron diffraction patterns from quasicrystals in AI-Mn and Mg-AI-Zn-Cu alloys revealed interesting differences. These are interpreted here on the basis of variation in 'local isomorphism' (13).

Research paper thumbnail of Electron microscopy of quasi-crystals in rapidly solidified Al-14% Mn alloys

Scripta Metallurgica, 1985

Research paper thumbnail of The ω Phase Formation during Laser Cladding and Remelting of Quasicrystal Forming AlCuFe on Pure Aluminum

MRS Proceedings, 2003

ABSTRACTWe report the formation ω phase in the remelted layers during laser cladding and remeltin... more ABSTRACTWe report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω ...

Research paper thumbnail of Continuous welding of Cu–Ni dissimilar couple using CO 2 laser

Science and Technology of Welding and Joining, 2005

The evolution of microstructure during continuous laser welding of dissimilar metals has been stu... more The evolution of microstructure during continuous laser welding of dissimilar metals has been studied for a binary Cu-Ni couple. The effects of laser beam scan speed and laser power on the shape and size of the melt pool, the weldment-substrate interface, the composition profiles, and microstructures of the weldments have been investigated. It is shown that the melt pools exhibit a characteristic asymmetry in shape. The observed microstructure is characterised by the existence of compositional and microstructural variations leading to a banded appearance suggesting localised mixing. Distinct differences exist in the evolution of the microstructure in the copper and nickel sides of the weld pool. An attempt is made to explain some of the experimental observations using thermodynamic and thermal transport arguments.

Research paper thumbnail of Solidification microstructure development

Sadhana, 2001

In the present article, evolution of microstructure during solidification, as a function of vario... more In the present article, evolution of microstructure during solidification, as a function of various parameters, is discussed. Macrosegregation is described as being due to insufficient diffusivity of solute in the solid. Pattern formation is discussed in the light of instabilities at the solidification growth front. An overview of the scaling relations for various microstructures is given. Metastable extensions to equilibrium phase diagrams and corrections to equilibrium quantities are described.

Research paper thumbnail of Characterization of a continuous CO2 laser-welded Fe-Cu dissimilar couple

Metallurgical and Materials Transactions A, 2005

Continuous CO 2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different ... more Continuous CO 2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different process conditions is studied. The process conditions are varied to identify and characterize the microstructural features that are independent of the welding mode. The study presents a characterization of the microstructure and mechanical properties of the welds. Detailed microstructural analysis of the weld/base-metal interface shows features that are different on the two sides of the weld. The iron side can grow into the weld with a local change in length scale, whereas the interface on the copper side indicates a barrier to growth. The interface is jagged, and a banded microstructure consisting of iron-rich layers could be observed next to the weld/Cu interface. The observations suggest that solidification initiates inside the melt, where iron and copper are mixed due to convective flow. The transmission electron microscopy (TEM) of the weld region also indicates the occasional presence of droplets of iron and copper. The microstructural observations are rationalized using arguments drawn from a thermodynamic analysis of the Fe-Cu system.

Research paper thumbnail of Microstructural evolution during remelting of laser surface alloyed hyper-monotectic Al–Bi alloy

Materials Science and Engineering: A, 2004

The present investigation explores the possibility of synthesizing a two-phase microstructure con... more The present investigation explores the possibility of synthesizing a two-phase microstructure consisting of a fine dispersion of bismuth particles in an aluminium matrix using the laser surface alloying technique. The possibility of controlling the size distribution of bismuth particles by subsequent remelting is also investigated. The microstructural analysis of the surface alloyed samples shows that the average size of the bismuth particles reduces with increase in laser scan speed. In order to understand the factors that determine the nature of the size distribution of the particles, a detailed model is developed. The model incorporates heat and fluid flow induced by the laser to arrive at the evolution of the temperature and velocity of the melt in three dimensions. Using these as inputs, a kinetic analysis of the nucleation, growth and coarsening induced by collision-controlled coalescence of the bismuth particles from the melt is carried out. Comparison with the experiments indicates that coalescence due to convection plays an important role in the evolution of the size distribution of bismuth particles.

Research paper thumbnail of Microstructure evolution in laser alloyed layer of Cu–Fe–Al–Si on Cu substrate

Materials Science and Engineering: A, 2004

Laser alloyed layers of Cu-Fe-Al-Si were prepared using an 8 kW CO 2 laser on copper substrate an... more Laser alloyed layers of Cu-Fe-Al-Si were prepared using an 8 kW CO 2 laser on copper substrate and a detailed TEM investigation of the cross-section microstructure was carried out. This paper elucidates on the sequence of evolution of various phases constituting a complex microstructure due to non-equilibrium solidification of the laser alloyed layer. The formation of micron size Fe-rich globules having DO 3 structure within Cu-rich fcc matrix suggests access to a submerged miscibility gap during the laser processing. The solute rejection processes during later stages of solidification and solid state cooling result in the evolution of submicron size Cu-rich dispersoids inside the Fe-rich globules and the Fe-rich nanoscale fully coherent precipitates within the surrounding Cu-rich matrix.

Research paper thumbnail of Non-equilibrium solidification of concentrated Fe–Ge alloys

Materials Science and Engineering: A, 2007

Research paper thumbnail of Laser cladding of quasicrystal forming Al–Cu–Fe on aluminum

Journal of Non-Crystalline Solids, 2004

Composite quasicrystalline coatings are developed by laser cladding of an elemental powder mixtur... more Composite quasicrystalline coatings are developed by laser cladding of an elemental powder mixture of aluminum, copper and iron on an aluminum substrate. Some of the tracks are remelted to see the effect of phase formation and related changes in hardness during remelting. The clad layers start growing with a cellular morphology from the substrate. The icosahedral phase forms in all the tracks along with some aluminides. It has also been found that the icosahedral phase forms both by a peritectic reaction between the liquid and Al 13 Fe 4 and by direct nucleation from the liquid. This is a clear indication of a different levels of undercooling that the liquid undergoes before the nucleation of the primary phase inside the clad layers during laser processing. The formation of Al 13 Fe 4 with a ten-pointed star like morphology has also been found at the bottom of the clad. The remelting of the clad tracks leads to a change in microstructure as far as phase formation is concerned. The formation of long lath-shaped Al 13 Fe 4 can be observed in the remelted layer. The hardness profiles of the clad and remelted layers reveal a hardness (HV 0:025) around 600.

Research paper thumbnail of Densification and microstructure development in spark plasma sintered WC–6 wt% ZrO2 nanocomposites

Journal of Materials Research, 2007

In this paper, we report the results of a transmission electron microscopy investigation on WC–6 ... more In this paper, we report the results of a transmission electron microscopy investigation on WC–6 wt% ZrO2nanocomposite, spark plasma sintered at 1300 °C, for varying times of up to 20 min. The primary aim of this work was to understand the evolution of microstructure during such a sintering process. The investigation revealed the presence of nanocrystalline ZrO2particles (30–50 nm) entrapped within submicron WC grains. In addition, relatively coarser ZrO2(60–100 nm) particles were observed to be either attached to WC grain boundaries or located at WC triple grain junctions. The evidence of the presence of a small amount of W2C, supposed to have been formed due to sintering reaction between WC and ZrO2, is presented here. Detailed structural investigation indicated that ZrO2in the spark plasma sintered nanocomposite adopted an orthorhombic crystal structure, and the possible reasons for o-ZrO2formation are explained. The increase in kinetics of densification due to the addition of Zr...

Research paper thumbnail of Microstructural evolution in laser-ablation-deposited Fe–25 at.% Ge thin film

Journal of Materials Research, 2006

Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single cry... more Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single crystal NaCl and Cu substrates at room temperature. Both the vapor and liquid droplets generated in this process are quenched on the substrate. The microstructures of the embedded droplets show size as well as composition dependence. The hierarchy of phase evolution from amorphous to body-centered cubic (bcc) to DO3 has been observed as a function of size. Some of the medium-sized droplets also show direct formation of ordered DO19 phase from the starting liquid. The evolution of disordered bcc structure in some of the droplets indicates disorder trapping during liquid to solid transformation. The microstructural evolution is analyzed on the basis of heat transfer mechanisms and continuous growth model in the solidifying droplets.

Research paper thumbnail of Melting and superheating of metals and alloys

Progress in Materials Science, 1997

Research paper thumbnail of Depression of melting point of multidomained bismuth in aluminum based metallic glass nanocomposites

Applied Physics Letters, 1996

Research paper thumbnail of Melting of Bi nanoparticles embedded in a Zn matrix

Acta Materialia, 2004

We report the melting behavior of nanometric-Bi particles embedded in the zinc matrix synthesized... more We report the melting behavior of nanometric-Bi particles embedded in the zinc matrix synthesized by the rapid solidification processing. These particles have specific orientation relation with the matrix given by {0 0 0 1} Zn i{1 0-1 2} Bi and AE1 1-2 0ae Zn nearly iAE1-2 1 0ae Bi. A change in melting behavior is observed on thermal cycling. The differential scanning calorimetry (DSC) results reveal that a fraction of Bi particles melts at 91-95 K below the bulk melting temperature during the second DSC-cycle. It is shown that the division of a single crystalline nano-Bi particle into several grains during solidification results in the significant reduction in melting, which can be explained by the phenomenological theory of melting.

Research paper thumbnail of Solidification of undercooled peritectic Fe–Ge alloy

Acta Materialia, 2005

Bulk samples of Fe-25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic ... more Bulk samples of Fe-25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic levitation technique. The growth rate of the primary phase is measured using a capacitance proximity sensor technique. Solidification microstructure is studied as a function of undercooling. The microstructure of samples at low undercoolings consists of a residual primary phase a 2 , peritectic phase e and inter-dendritic e-b eutectic. Microstructure at higher undercoolings is nearly phase-pure e. Time resolved diffraction analysis of the levitated droplets using synchrotron radiation indicates the nucleation of primary a 2 in all cases. The growth rate is analysed using current theories to explain the experimental observations. Interfacial undercooling is found to play an important role in the growth kinetics. Our results also suggest suppression of peritectic reaction.

Research paper thumbnail of The Role of Interfaces in Diffusional Growth

Research paper thumbnail of Behaviour of Embedded Metals and Alloys at Small Sizes

Research paper thumbnail of Morphogenesis and mechanostabilization of complex natural and 3D printed shapes

Science Advances, 2015

The natural selection and the evolutionary optimization of complex shapes in nature are closely r... more The natural selection and the evolutionary optimization of complex shapes in nature are closely related to their functions. Mechanostabilization of shape of biological structure via morphogenesis has several beautiful examples. With the help of simple mechanics-based modeling and experiments, we show an important causality between natural shape selection as evolutionary outcome and the mechanostabilization of seashells. The effect of biological growth on the mechanostabilization process is identified with examples of two natural shapes of seashells, one having a diametrically converging localization of stresses and the other having a helicoidally concentric localization of stresses. We demonstrate how the evolved shape enables predictable protection of soft body parts of the species. The effect of bioavailability of natural material is found to be a secondary factor compared to shape selectivity, where material microstructure only acts as a constraint to evolutionary optimization. T...

Research paper thumbnail of Hardness behaviour of ultrafine dispersed materials with soft dispersoids: The case of rapidly solidified Zn-Bi immiscible alloy

Scripta Metallurgica et Materialia, 1993

ABSTRACT

Research paper thumbnail of An electron microscopic study of quasicrystals in a quaternary alloy : Mg32(Al, Zn, Cu)49

Scripta Metallurgica, 1986

The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapi... more The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapidly solidified Al-14at%Mn alloy has activated intensive studies of a new class of solids, termed as quasicrystals (2). While the original discovery reported the existence of quasicrystals in AI-Mn. AI-Fe and AI-Cr alloys, subsequent work has revealed their existence in Mg-Zn-Al(3,4), Mg-A]-Cu(5), AI-Mn-Si(6) and Ti-Ni-V(7) alloys (Table l). We had earlier reported on the variety of electron diffraction patterns from quasicrystals h~ AI-Mn alloys (g-10). Ramachandrarao and Sastry (3) had argued the existence of quasicrystals in Mg-Zn-AI and Mg-AI-Cu alloys on the basis of the prevalence of icosahedrai coordination in crystalline Mg32(AI, Zn)49 structure~ as was demonstrated by Bergman et. al. (ll). The quaternary system Mg-AI-Zn-C~ had been investigated much earlier by Strawbridge et. al. (12). Fig. 1 gives from their classical work the domain of existence of the crystalline T-phase in the quaternary system Mg-AI-Zn-Cu. We felt that this quaternary alloy should also give rise to quasicrystals with additional stability endowed by the addition of Cu. A comparison of electron diffraction patterns from quasicrystals in AI-Mn and Mg-AI-Zn-Cu alloys revealed interesting differences. These are interpreted here on the basis of variation in 'local isomorphism' (13).

Research paper thumbnail of Electron microscopy of quasi-crystals in rapidly solidified Al-14% Mn alloys

Scripta Metallurgica, 1985