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Research Interests:
Transient plastic phase processing is a form of reactive hot pressing for fabricating fully dense ceramic‐ceramic composites at relative low homologous temperatures. In this study, this technique has been used on two powder mixtures—4:1... more
Transient plastic phase processing is a form of reactive hot pressing for fabricating fully dense ceramic‐ceramic composites at relative low homologous temperatures. In this study, this technique has been used on two powder mixtures—4:1 Ti/B4C and 1:1 TiC0.5/TiB2, which are equivalent in terms of elemental compositions—to produce fully dense titanium carbide‐titanium boride composites. The composites formed in each case are comprised of the same final phases—TiCx, TiB2, and Ti3B4, in roughly the same volume fractions—but exhibit distinctly different grain morphologies. Ti3B4 phase nucleates and grows as platelets for the 4:1 Ti/B4C starting composition but as equiaxed grains for the 1:1 TiC0.5/TiB2 composition. TiB has been identified as an intermediate phase in the “platelet” composition and appears to be important to the development of the Ti3B4 platelets. X‐ray diffractometry and scanning electron microscopy results indicate that the evolution of the microstructure is governed by...
Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Microstructure, Scanning Electron Microscopy, and 14 moreTitanium, Composite Material, Ceramic, X ray diffraction, Boron Carbide, Scanning Electron Microscope, Microstructures, Titanium Carbide, Chemical Composition, Bulk Density, Volume Fraction, Microstructure evolution, Mechanical Property, and Elemental composition
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Summary The effect of pressure cycling on the densification and ejection of Pb-Al 2 O 3 powder-mixtures is investigated and compared to static loading for volume fractions of Al 2 O 3, between 0 and 80%. The density of all mixtures... more
Summary The effect of pressure cycling on the densification and ejection of Pb-Al 2 O 3 powder-mixtures is investigated and compared to static loading for volume fractions of Al 2 O 3, between 0 and 80%. The density of all mixtures increases with time under constant pressure even at room temperature. This mechanical behavior is the result of the creep of lead. This effect diminishes with increasing volume fraction of Al 2 O 3. Pressure cycling does not have any influence on the final density of lead samples but becomes important ...
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Research Interests:
Research Interests: Mechanical Engineering, Chemical Engineering, Materials Science, Powder Metallurgy, Powder technology, and 11 morePorosity, Composite Material, Relative Density, Validation Studies, Compaction, Cross Section, Porous Material, Pressure Sensor, Coefficient of Friction, Microcrystalline Cellulose, and PHENOMENOLOGICAL MODEL
Research Interests: Materials Science, Medicine, Coating, Physical sciences, Metal, and 3 moreWhisker, Driving force, and Whiskers
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Ambient‐ and high‐temperature properties of a class of titanium carbide‐titanium boride composites that have been produced by transient plastic phase processing are presented. The composites produced are comprised of Ti3B4, TiB2, and... more
Ambient‐ and high‐temperature properties of a class of titanium carbide‐titanium boride composites that have been produced by transient plastic phase processing are presented. The composites produced are comprised of Ti3B4, TiB2, and TiC0.65 at their equilibrium composition (34.5, 30.5, and 34.9 vol%, respectively), and the Ti3B4 phase in these composites occurs either as equiaxed grains or as platelets, depending on the starting mixture composition. Measurements of the ambient‐ and high‐temperature flexure strength and fracture toughness, thermal shock susceptibility, oxidation resistance, and wear resistance of this class of composites are presented. The role of various microstructural parameters—such as the morphology of the Ti3B4 phase, the length scale of the microstructure, and the volume fraction of borides—on these properties has been identified.
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Research Interests:
Sintering aided by pulsed electric current offers the advantage of accelerated densification for a variety of powders. In this work, we employ numerical simulations in order to understand the distributions of current and temperature... more
Sintering aided by pulsed electric current offers the advantage of accelerated densification for a variety of powders. In this work, we employ numerical simulations in order to understand the distributions of current and temperature within the punch/die/specimen assembly. A thermalelectrical finite element model (FEM) with temperature and density dependent thermal and electrical properties is implemented. Electric and temperature fields during sintering of alumina (electrically non-conductive) and solid graphite plug ( ...
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Abstract Realistic microstructures of compacted powders formed by spark plasma sintering or field-activated sintering technology were modeled using the discrete finite-element method. Two key thermoelectric characteristics were... more
Abstract Realistic microstructures of compacted powders formed by spark plasma sintering or field-activated sintering technology were modeled using the discrete finite-element method. Two key thermoelectric characteristics were studied:(1) the effect of the electric current pattern, ie, direct current (DC) and pulsed current, on temperature distributions in the compacted powders, and (2) the effect of compaction modes, ie, isostatic compaction and uniaxial compaction, on conductivity. Simulations showed that, for the same electric power ...
Research Interests: Materials Science, Finite Element Methods, Modeling, Electronic Materials, Discrete Element Method, and 12 moreFinite element method, Anisotropy, Conductivity, Temperature Distribution, Finite element simulation, Microstructures, Spark Plasma Sintering, Electric Power, Experimental Measurement, Spark Plasma Sintering (SPS), Electrical And Electronic Engineering, and Direct Current
Heat transport through porous materials is a fundamental problem in many engineering applications including several powder metallurgy processes. In this work, we analyze the effect of compaction mode on the thermal conductivity of... more
Heat transport through porous materials is a fundamental problem in many engineering applications including several powder metallurgy processes. In this work, we analyze the effect of compaction mode on the thermal conductivity of compacts in closed die compaction and hydrostatic compaction by a two-dimensional (2D) Discrete Finite Element Method (DFEM). The simulations show that the effective thermal conductivity increases with the relative density as expected. However, an anisotropy of conductivity develops in the ...
Low frequency electric field has been applied to particulate system in many techniques. A typical problem in such processes is the localization of the current in few discrete paths in the material. It causes the inhomogeneous temperature... more
Low frequency electric field has been applied to particulate system in many techniques. A typical problem in such processes is the localization of the current in few discrete paths in the material. It causes the inhomogeneous temperature distribution. In this paper we utilize discrete element method (DEM) that elucidates this phenomenon. We demonstrate that pulse current can be used to provide more uniform distribution of the temperature in the system. Relative density (pressure is often applied simultaneously with electric current) ...
A multi-particle finite element model (MPFEM) was used to explore the densification yield surfaces of a collection of monosize particles in 2-D. Individual particles discretized with a finite element mesh allow for a full description of... more
A multi-particle finite element model (MPFEM) was used to explore the densification yield surfaces of a collection of monosize particles in 2-D. Individual particles discretized with a finite element mesh allow for a full description of the contact mechanics and the local and global particle kinematics. Compaction modes ranging from hydrostatic to that of high shear are studied for various levels of interparticle friction. Isodensity curves in stress-space during densification are shown to take the equivalent shape of a cap and cone model whose ...
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Research Interests:
ABSTRACT In an effort to identify the origin and the evolution of damage during the compaction/ejection cycle of powder compacts, an experimental study that compares compacts in straight and tapered dies in terms of the presence and... more
ABSTRACT In an effort to identify the origin and the evolution of damage during the compaction/ejection cycle of powder compacts, an experimental study that compares compacts in straight and tapered dies in terms of the presence and growth of microcracks was carried out using x-ray tomography and environmental scanning electron microscopy. The results presented here document the presence of internal microcracks at high relative densities, and microcracks on the surface of the compacts. Parts compacted in tapered dies exhibit microcracks with smaller crack tip opening and have a higher axial strength than those made in a straight die. These experimental observations, together with the ideas of damage generation under compressive stresses, as well as finite element analysis of the stress field in the compact as it exits from the die, confirm the hypothesis that a two-step mechanism is responsible for damage generation in powder compacts. First, microcracking occurs during unloading within the die at high pressures and subsequently surface cracks grow under the localized stresses as the compact emerges from the die.
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Research Interests:
Abstract The mechanical behavior of alloys in the semisolid state is very sensitive to the volume fraction of solid. In this paper, a simple criterion for processability in the semisolid range is introduced, based on the sensitivity of... more
Abstract The mechanical behavior of alloys in the semisolid state is very sensitive to the volume fraction of solid. In this paper, a simple criterion for processability in the semisolid range is introduced, based on the sensitivity of the volume fraction of solid with respect to minor temperature variations. In addition it is proposed that the processability in the semisolid state can be enhanced using microsegregated material.
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Research Interests:
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Experimental evidence is presented showing that the rolling strain required to produce internal necking in clad sheet depends both on the volume fraction of each constituent in the clad and the geometry of the rolls. This result was not... more
Experimental evidence is presented showing that the rolling strain required to produce internal necking in clad sheet depends both on the volume fraction of each constituent in the clad and the geometry of the rolls. This result was not predicted by earlier localization analysis that approximates the stress/strain field in rolling with that of plane strain compression. The evolution of hardness during rolling and complementary finite element results point to redundant shearing of the soft phase as the reason for this behavior. Such ...
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One of primary goals of the Quality by Design initiative in the pharmaceutical industry is to reduce variation in the product quality through increased understanding and control of the manufacturing process. In the case of roller... more
One of primary goals of the Quality by Design initiative in the pharmaceutical industry is to reduce variation in the product quality through increased understanding and control of the manufacturing process. In the case of roller compaction, in which mixtures of active and inert powders are fed via a screw to counter-rotating rolls, drawn into the nip region and compacted under hydrostatic and shear stresses, variation in density of the roller compacted material has been commonly observed. In the experimental part of this work we report ...
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Abstract: The modelling needs of Solid Oxide Fuel Cell is exemplified by considering two key problems of high temperature cell processing and operation. During processing of cells a one step sintering of a two phase layered structure is... more
Abstract: The modelling needs of Solid Oxide Fuel Cell is exemplified by considering two key problems of high temperature cell processing and operation. During processing of cells a one step sintering of a two phase layered structure is applied called cofiring. Due to different shrinkage rates of both components it results in a more or less intense bending of the planar fuel cell unit which should be minimized. The modelling attempt leads to the introduction of a viscous sintering model allowing the calculation of the deflection ...
A multi-particle finite element model (MPFEM) was used to explore the densification yield surfaces of a collection of monosize particles in 2-D. Individual particles discretized with a finite element mesh allow for a full description of... more
A multi-particle finite element model (MPFEM) was used to explore the densification yield surfaces of a collection of monosize particles in 2-D. Individual particles discretized with a finite element mesh allow for a full description of the contact mechanics and the local and global particle kinematics. Compaction modes ranging from hydrostatic to that of high shear are studied for various levels of interparticle friction. Isodensity curves in stress-space during densification are shown to take the equivalent shape of a cap and cone model whose ...