The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Eugene A. Olevsky - One of the best experts on this subject based on the ideXlab platform.
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densification of zirconium nitride by spark plasma sintering and high voltage Electric Discharge consolidation a comparative analysis
Ceramics International, 2015Co-Authors: Maria Yurlova, E. G. Grigoryev, Eugene A. Olevsky, Diletta Giuntini, O L Khasanov, Joanna MckittrickAbstract:Abstract The densification behavior of zirconium nitride powder is investigated for various temperature and pressure conditions imposed by spark plasma sintering and high voltage Electric Discharge consolidation techniques. The crystal structure, chemical composition, porosity, and grain size of the powders and processed specimens are analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The outcomes of the two considered consolidation techniques are comparatively assessed. Vickers micro-hardness of the processed ZrN specimens is investigated, and hardness dependence on porosity is analyzed. The densification mechanism of ZrN consolidated by spark plasma sintering is revealed by applying the constitutive equation of the continuum theory of sintering, and it turns out to be a similar mechanism to hot pressing. Application of the sintering constitutive equations shows that the mechanism of ZrN densification by high voltage Electric Discharge consolidation method depends on the magnitude of the applied voltage.
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Thermal processes during high-voltage Electric Discharge consolidation of powder materials
Scripta Materialia, 2012Co-Authors: E. G. Grigoryev, Eugene A. OlevskyAbstract:The results of a simulation of the thermal processes occurring within interparticle contacts of powder materials under high-voltage Electric Discharge consolidation are presented. The thermal processes in the contacts between powder particles are characterized by significant spatial inhomogeneity and time dependence. The determination of the behavior of the interparticle contact zones enables optimization of the pulse Electrical current parameters. A good correlation between the modeling and experimental data for compacted iron and heat-resistant steel powders is demonstrated.
Bulent Ekmekci - One of the best experts on this subject based on the ideXlab platform.
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debris and consequences in micro Electric Discharge machining of micro holes
International Journal of Machine Tools & Manufacture, 2013Co-Authors: Bulent Ekmekci, Atakan SayarAbstract:Abstract The tip shape of a blind micro-hole produced using micro Electrical Discharge machining varies with respect to the process parameters used during machining. The usual tip shape is a blunt geometry within the common range of applications, however, under specific machining conditions and machining depths, the tip shape changes drastically to an inverted concaved shape. The origin of such tip deformation in micro Electric Discharge machining of blind micro-holes was investigated. It was observed that debris particles produced during machining accumulated at the tip, formed a hill and functioned as a tool electrode especially when using fine machining conditions. The phenomena is elaborated experimentally with the affecting parameters to describe the wear mechanism. Open gap voltage, pulse energy and tool rotation speed are examined as varying parameters during the experiments.
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residual stresses and white layer in Electric Discharge machining edm
Applied Surface Science, 2007Co-Authors: Bulent EkmekciAbstract:The effect of diElectric liquid and electrode type on white layer structure in Electric Discharge machined surfaces has been studied in terms of retained austenite and residual stresses using X-ray diffraction method. The machining tests were conducted by using two different tool electrodes (copper and graphite) and diElectric liquid (kerosene and de-ionized water) under same operational conditions. The present work suggests that the surface is saturated with carbon irrespective of the tool electrode material when machining with kerosene diElectric liquid. But, retained austenite is formed on the surface due to carbon uptake from graphite tool electrode when machining with de-ionized water diElectric liquid. On the other hand, even though surface residual stresses increase with structural non-homogeneities in the white layer, no clear consequences have been observed in residual stress distribution beneath the white layer.
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a semi empirical approach for residual stresses in Electric Discharge machining edm
International Journal of Machine Tools & Manufacture, 2006Co-Authors: Bulent Ekmekci, Erman A Tekkaya, Abdulkadir ErdenAbstract:High residual stresses are developed on the surfaces of Electric Discharge machined parts. In this study, layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function.
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residual stress state and hardness depth in Electric Discharge machining de ionized water as diElectric liquid
Machining Science and Technology, 2005Co-Authors: Bulent Ekmekci, Oktay Elkoca, Erman A Tekkaya, Abdulkadir ErdenAbstract:ABSTRACT Procedures and results of experimental work to measure residual stresses and hardness depth in Electric Discharge machined surfaces are presented. Layer removal method is used to express the residual stress profile as a function of depth caused by a die sinking type EDM. Thin stressed layers are removed from machined samples by electrochemical machining. Corresponding deformations due to stress relaxation are recorded for each removal to determine the stress profile from elasticity theory. The relational dependence of the machining parameters with residual stresses is obtained and a semi-empirical model is proposed for plastic mold steel for de-ionized water as diElectric liquid. These stresses are found to be increasing rapidly with respect to depth, attaining to its maximum value, around the yield strength, and then fall rapidly to compressive residual stresses in the core of the material since the stresses within plastically deformed layers are equilibrated with elastic stresses.
Wayne C Solomon - One of the best experts on this subject based on the ideXlab platform.
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continuous wave laser oscillation in subsonic flow on the 1315nm atomic iodine transition pumped by Electric Discharge produced o2 aδ1
Applied Physics Letters, 2006Co-Authors: J T Verdeyen, David L Carroll, Darren M King, J K Laystrom, G F Benavides, J W Zimmerman, Brian S Woodard, Wayne C SolomonAbstract:Herein the authors report on the demonstration of a continuous-wave laser in subsonic flow on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited Electric Discharge. The Electric Discharge was sustained in an O2–He–NO gas mixture. Downstream of the Discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow to shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 540mW in a stable cavity with two 99.993% reflective mirrors.
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measurement of positive gain on the 1315nm transition of atomic iodine pumped by o2 a1δ produced in an Electric Discharge
Applied Physics Letters, 2004Co-Authors: David L Carroll, J T Verdeyen, Darren M King, J K Laystrom, J W Zimmerman, Brian S Woodard, N Richardson, K Kittell, Mark J Kushner, Wayne C SolomonAbstract:Laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ), which is produced using wet-solution chemistry. The system difficulties of chemically producing O2(a1Δ) has motivated investigations into gas phase methods to produce O2(a1Δ) using low-pressure Electric Discharges. In this letter we report on positive gain on the 1315nm transition of atomic iodine where the O2(a1Δ) was produced in a flowing Electric Discharge. The Electric Discharge was followed by a continuously flowing supersonic cavity that was necessary to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(P1∕22) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the measurements of gain.
David L Carroll - One of the best experts on this subject based on the ideXlab platform.
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continuous wave laser oscillation in subsonic flow on the 1315nm atomic iodine transition pumped by Electric Discharge produced o2 aδ1
Applied Physics Letters, 2006Co-Authors: J T Verdeyen, David L Carroll, Darren M King, J K Laystrom, G F Benavides, J W Zimmerman, Brian S Woodard, Wayne C SolomonAbstract:Herein the authors report on the demonstration of a continuous-wave laser in subsonic flow on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited Electric Discharge. The Electric Discharge was sustained in an O2–He–NO gas mixture. Downstream of the Discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow to shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 540mW in a stable cavity with two 99.993% reflective mirrors.
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continuous wave laser oscillation on the 1315nm transition of atomic iodine pumped by o2 a1δ produced in an Electric Discharge
Applied Physics Letters, 2005Co-Authors: David L Carroll, J T Verdeyen, Darren M King, J K Laystrom, G F Benavides, J W Zimmerman, Brian S Woodard, K Kittell, Shane D Stafford, Mark J KushnerAbstract:Laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ) which is produced using wet-solution chemistry. The difficulties in chemically producing O2(a1Δ) has motivated investigations into purely gas phase methods to produce O2(a1Δ) using low-pressure Electric Discharges. In this letter, we report on the demonstration of a continuous-wave laser on the 1315nm transition of atomic iodine where the O2(a1Δ) used to pump the iodine was produced by a radio-frequency-excited Electric Discharge. The Electric Discharge was sustained in a He∕O2 gas mixture upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 220mW in a stable cavity composed of two 99.99% reflective mirrors.
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measurement of positive gain on the 1315nm transition of atomic iodine pumped by o2 a1δ produced in an Electric Discharge
Applied Physics Letters, 2004Co-Authors: David L Carroll, J T Verdeyen, Darren M King, J K Laystrom, J W Zimmerman, Brian S Woodard, N Richardson, K Kittell, Mark J Kushner, Wayne C SolomonAbstract:Laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ), which is produced using wet-solution chemistry. The system difficulties of chemically producing O2(a1Δ) has motivated investigations into gas phase methods to produce O2(a1Δ) using low-pressure Electric Discharges. In this letter we report on positive gain on the 1315nm transition of atomic iodine where the O2(a1Δ) was produced in a flowing Electric Discharge. The Electric Discharge was followed by a continuously flowing supersonic cavity that was necessary to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(P1∕22) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the measurements of gain.
E. G. Grigoryev - One of the best experts on this subject based on the ideXlab platform.
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densification of zirconium nitride by spark plasma sintering and high voltage Electric Discharge consolidation a comparative analysis
Ceramics International, 2015Co-Authors: Maria Yurlova, E. G. Grigoryev, Eugene A. Olevsky, Diletta Giuntini, O L Khasanov, Joanna MckittrickAbstract:Abstract The densification behavior of zirconium nitride powder is investigated for various temperature and pressure conditions imposed by spark plasma sintering and high voltage Electric Discharge consolidation techniques. The crystal structure, chemical composition, porosity, and grain size of the powders and processed specimens are analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The outcomes of the two considered consolidation techniques are comparatively assessed. Vickers micro-hardness of the processed ZrN specimens is investigated, and hardness dependence on porosity is analyzed. The densification mechanism of ZrN consolidated by spark plasma sintering is revealed by applying the constitutive equation of the continuum theory of sintering, and it turns out to be a similar mechanism to hot pressing. Application of the sintering constitutive equations shows that the mechanism of ZrN densification by high voltage Electric Discharge consolidation method depends on the magnitude of the applied voltage.
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Thermal processes during high-voltage Electric Discharge consolidation of powder materials
Scripta Materialia, 2012Co-Authors: E. G. Grigoryev, Eugene A. OlevskyAbstract:The results of a simulation of the thermal processes occurring within interparticle contacts of powder materials under high-voltage Electric Discharge consolidation are presented. The thermal processes in the contacts between powder particles are characterized by significant spatial inhomogeneity and time dependence. The determination of the behavior of the interparticle contact zones enables optimization of the pulse Electrical current parameters. A good correlation between the modeling and experimental data for compacted iron and heat-resistant steel powders is demonstrated.