The Experts below are selected from a list of 122991 Experts worldwide ranked by ideXlab platform
Fevzi Bedir - One of the best experts on this subject based on the ideXlab platform.
-
modelling of deformation and microstructural changes in p m rene 95 under isothermal forging conditions
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Oktay M Alniak, Fevzi BedirAbstract:Abstract The changes in microstructure induced by forging and their influence on Flow Strength of hot isostatically pressed P/M Rene 95 as revealed by constant strain rate compression tests under simulated isothermal forging conditions are discussed. Results are presented for initially fine (7 μm) and coarse (50 μm) grained compacts tested at temperatures of 1050, 1075 and 1100 °C and at strain rates in the range from 10−4 to 1 s−1. Under these test conditions, both the fine and coarse-grained compacts recrystallize and their grain size is refined during plastic deformation. This grain refinement gives rise to softening in both materials. Ultimately, their microstructures transform into the same equiaxed fine-grained microduplex structure at which point their Flow Strength becomes identical. Continued deformation at that point produces no further change in grain size or Flow Strength. In this regime of deformation, the microduplex grain size and Flow Strength are independent of the original microstructure but are conditioned by the strain rate at a given temperature. The steady state grain size increases whereas the steady Flow Strength decreases with a decrease in strain rate and/or an increase in temperature. It is shown how changes in microstructure and Flow Strength during isothermal forging can be modelled in P/M Rene 95 compacts by means of established deformation models for predicting peak Flow Strength, using the steady state deformation data as a boundary condition for the evolution of microstructure and Flow Strength and a model for deformation-induced recrystallization during forging that has been recently developed for this class of materials.
-
change in grain size and Flow Strength in p m rene 95 under isothermal forging conditions
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2006Co-Authors: Oktay M Alniak, Fevzi BedirAbstract:Abstract The changes in microstructure induced by plastic deformation in hot isostatically pressed (HIPed) P/M Rene 95 under isothermal conditions are discussed. Results of the constant true strain rate compression tests are presented for initially fine (7 μm) and coarse (50 μm) grained compacts deformed at temperatures of 1050 °C, 1075 °C and 1100 °C and at strain rates in the range from 10 −4 s −1 to 1 s −1 . Under these test conditions, both the fine and coarse-grained compacts recrystallize and their grain size are refined during Flow. This grain refinement gives rise to softening in both materials. Ultimately, their microstructures transform into the same equiaxed fine-grained microduplex structure at which point their Flow Strength becomes identical. Continued deformation at that point produces no further change in grain size or Flow Strength. Under this steady state regime of deformation, the microduplex grain size and Flow Strength are independent of the original microstructure but are conditioned by the strain rate at a given temperature. The steady state grain size increases whereas the steady Flow Strength decreases with a decrease in strain rate and/or an increase in temperature.
Keqing Xia - One of the best experts on this subject based on the ideXlab platform.
-
azimuthal motion reorientation cessation and reversal of the large scale circulation in turbulent thermal convection a comparative study in aspect ratio one and one half geometries
Physical Review E, 2008Co-Authors: Keqing XiaAbstract:We report a systematic experimental study of the orientation and the Flow Strength of the large-scale circulation (LSC) in water-filled cylindrical Rayleigh-B\'enard convection cells with aspect ratios 2.3, 1, and 0.5 by both direct velocity measurement and the indirect multithermal-probe measurement. Unlike its weak effect in the system's global heat transport, the aspect ratio $\ensuremath{\Gamma}$ is found to play an important role in the dynamics of the azimuthal motion of the LSC. It is found that in larger $\ensuremath{\Gamma}$ geometries the azimuthal motion of the LSC's vertical plane is confined in smaller azimuthal region than that in smaller $\ensuremath{\Gamma}$ geometries. The twisting motion between top and bottom parts of the LSC observed in the $\ensuremath{\Gamma}=1$ geometry is found to be absent in the $\ensuremath{\Gamma}=1∕2$ case. It is found that in the $\ensuremath{\Gamma}=1∕2$ geometry the orientational change $\ensuremath{\mid}\ensuremath{\Delta}\ensuremath{\phi}\ensuremath{\mid}$ through a reorientation has an exponential distribution, in contrast to the power-law distribution for the $\ensuremath{\Gamma}=1$ case. Despite the difference in orientational change, the occurrence of the reorientations is a Poisson process in both geometries. Using the conditional average of the time interval between adjacent cessations or reversals on the rebound Flow Strength, we demonstrate the possibility to empirically predict when the next cessation or reversal will most likely occur if the rebound Flow Strength of the preceding cessation or reversal is given.
-
azimuthal motion reorientation cessation and reversal of the large scale circulation in turbulent thermal convection a comparative study in aspect ratio one and one half geometries
Physical Review E, 2008Co-Authors: Keqing XiaAbstract:We report a systematic experimental study of the orientation and the Flow Strength of the large-scale circulation (LSC) in water-filled cylindrical Rayleigh-Benard convection cells with aspect ratios 2.3, 1, and 0.5 by both direct velocity measurement and the indirect multithermal-probe measurement. Unlike its weak effect in the system's global heat transport, the aspect ratio Gamma is found to play an important role in the dynamics of the azimuthal motion of the LSC. It is found that in larger Gamma geometries the azimuthal motion of the LSC's vertical plane is confined in smaller azimuthal region than that in smaller Gamma geometries. The twisting motion between top and bottom parts of the LSC observed in the Gamma=1 geometry is found to be absent in the Gamma=1/2 case. It is found that in the Gamma=1/2 geometry the orientational change mid R:Deltavarphimid R: through a reorientation has an exponential distribution, in contrast to the power-law distribution for the Gamma=1 case. Despite the difference in orientational change, the occurrence of the reorientations is a Poisson process in both geometries. Using the conditional average of the time interval between adjacent cessations or reversals on the rebound Flow Strength, we demonstrate the possibility to empirically predict when the next cessation or reversal will most likely occur if the rebound Flow Strength of the preceding cessation or reversal is given.
A Misra - One of the best experts on this subject based on the ideXlab platform.
-
deformation behavior of nanoscale al al2cu eutectics studied by in situ micropillar compression
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2021Co-Authors: Jian Wang, S J Wang, D Y Xie, A MisraAbstract:Abstract Deformation behavior of nanoscale laser processed Al–Al2Cu eutectics at room temperature is characterized through in situ micro-pillar compression testing in a scanning transmission microscope. Interlamellar spacing of Al–Al2Cu eutectics varies from hundreds of nanometers to 20 nm. Three different sizes of micro-pillars are fabricated in order to study the deformation behaviors of single colony and multiple colonies, corresponding to the single crystal and polycrystal respectively. For single colonies, lamellar orientations parallel, normal or inclined to the loading direction were tested. The main findings are: 1) the plasticity mechanisms strongly depend on loading orientation: buckling and kinking in the parallel-loaded eutectics, planar sliding along Al–Al2Cu lamellar interfaces in the incline-loaded eutectics and localized shearing in the normal-loaded eutectics. 2) the incline-loaded eutectics exhibits the lowest compression Flow Strength, and the normal-loaded eutectics has the highest compression Flow Strength. 3) with decreasing inter-lamellar spacing, the Strength increases and plasticity is uniformly distributed, as opposed to shear localization. Highest compressive plasticity is observed in polycrystalline eutectics with an ensemble of lamellar orientations with ~20 nm average spacing: 17.9% at Flow stress of 1.63 GPa, and degenerate, bimodal morphology: 11.1% at Flow stress of 1.36 GPa.
-
effect of laser surface remelting on the microstructure and properties of al al2cu si ternary eutectic alloy
Scientific Reports, 2017Co-Authors: Bhupendera Prashanth Ramakrishnan, A Misra, Qian Lei, Jyoti MazumderAbstract:Bimodal ultrafine eutectic composites (BUECs) exhibit a good combination of Strength and plasticity owing to a dual-hierarchy in eutectic length-scales in the microstructure. The present study investigates the variation of phase, morphology, feature length-scales and modality of microstructures obtained in a Al81Cu13Si6 (at. %) ternary alloy after laser surface remelting. A novel approach of varying component bimodal eutectic volume fractions by controlling the cooling rate of the laser solidification process has been presented. The volume fraction of the fine eutectic matrix has a profound effect on the Flow Strength. Laser remelted microstructures with volume fractions of the fine eutectic varying from 25 to 40% exhibiting compressive Flow Strengths ranging from 500 to 900 MPa have been obtained. The volume fraction of the fine eutectic decreased with cooling rate and completely ceased to exist at cooling rates greater than $$4\times {10}^{4}\,^\circ {\rm{C}}/{\rm{s}}$$ .
-
Strength and plasticity of nanolaminated materials
Materials research letters, 2017Co-Authors: Jian Wang, Qing Zhou, Shuai Shao, A MisraAbstract:ABSTRACTThe mechanical behavior of nanolaminates is dominated by interfaces that act as sources, barriers, and preferred sites for storage and dynamic recovery of glide dislocations. In this article, the deformation mechanisms of a variety of metal-based nanolaminates are reviewed with emphasis on unusual mechanical properties such as ultra-high Flow Strength without loss of plastic deformability.
-
plasticity evolution in nanoscale cu nb single crystal multilayers as revealed by synchrotron x ray microdiffraction
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: A S Budiman, Karthic R Narayanan, Jian Wang, Nobumichi Tamura, Martin Kunz, A MisraAbstract:Abstract In this study, the evolution of dislocation densities during compressive deformation of nanoscale Cu/Nb single crystal multilayers with individual layer thickness of 20 nm is investigated using Synchrotron X-ray micro-diffraction. The samples were subjected to successive compression straining up to a final cumulative strain of 35%. The nanolayer composite exhibited a maximum Flow Strength of ~1.6 GPa at approximately 24% compressive strain. Synchrotron X-ray micro-diffraction experiments, using a monochromatic beam of 10 keV energy were performed after each compression strain increment. We observed a significant increase in X-ray ring width peak broadening in both Cu and Nb layers up to strains of ~3.5% followed by saturation broadening at higher strains. This observation indicates that the interfaces of the Cu/Nb nanolayers are very effective in trapping and annihilating dislocation content during mechanical deformation.
-
deformability of ultrahigh Strength 5 nm cu nb nanolayered composites
Applied Physics Letters, 2008Co-Authors: Nathan A Mara, D Bhattacharyya, P O Dickerson, R G Hoagland, A MisraAbstract:In this work, micropillar compression testing has been used to obtain stress-strain curves for sputter-deposited Cu–Nb nanolaminate composites with nominal bilayer thickness of 10nm. In addition to the extremely high Flow Strength of 2.4GPa, the 5nm Cu∕5nm Nb nanolaminate exhibits significant ductility, in excess of 25% true strain.
Oktay M Alniak - One of the best experts on this subject based on the ideXlab platform.
-
modelling of deformation and microstructural changes in p m rene 95 under isothermal forging conditions
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Oktay M Alniak, Fevzi BedirAbstract:Abstract The changes in microstructure induced by forging and their influence on Flow Strength of hot isostatically pressed P/M Rene 95 as revealed by constant strain rate compression tests under simulated isothermal forging conditions are discussed. Results are presented for initially fine (7 μm) and coarse (50 μm) grained compacts tested at temperatures of 1050, 1075 and 1100 °C and at strain rates in the range from 10−4 to 1 s−1. Under these test conditions, both the fine and coarse-grained compacts recrystallize and their grain size is refined during plastic deformation. This grain refinement gives rise to softening in both materials. Ultimately, their microstructures transform into the same equiaxed fine-grained microduplex structure at which point their Flow Strength becomes identical. Continued deformation at that point produces no further change in grain size or Flow Strength. In this regime of deformation, the microduplex grain size and Flow Strength are independent of the original microstructure but are conditioned by the strain rate at a given temperature. The steady state grain size increases whereas the steady Flow Strength decreases with a decrease in strain rate and/or an increase in temperature. It is shown how changes in microstructure and Flow Strength during isothermal forging can be modelled in P/M Rene 95 compacts by means of established deformation models for predicting peak Flow Strength, using the steady state deformation data as a boundary condition for the evolution of microstructure and Flow Strength and a model for deformation-induced recrystallization during forging that has been recently developed for this class of materials.
-
change in grain size and Flow Strength in p m rene 95 under isothermal forging conditions
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2006Co-Authors: Oktay M Alniak, Fevzi BedirAbstract:Abstract The changes in microstructure induced by plastic deformation in hot isostatically pressed (HIPed) P/M Rene 95 under isothermal conditions are discussed. Results of the constant true strain rate compression tests are presented for initially fine (7 μm) and coarse (50 μm) grained compacts deformed at temperatures of 1050 °C, 1075 °C and 1100 °C and at strain rates in the range from 10 −4 s −1 to 1 s −1 . Under these test conditions, both the fine and coarse-grained compacts recrystallize and their grain size are refined during Flow. This grain refinement gives rise to softening in both materials. Ultimately, their microstructures transform into the same equiaxed fine-grained microduplex structure at which point their Flow Strength becomes identical. Continued deformation at that point produces no further change in grain size or Flow Strength. Under this steady state regime of deformation, the microduplex grain size and Flow Strength are independent of the original microstructure but are conditioned by the strain rate at a given temperature. The steady state grain size increases whereas the steady Flow Strength decreases with a decrease in strain rate and/or an increase in temperature.
Van Der Erik Giessen - One of the best experts on this subject based on the ideXlab platform.
-
discrete dislocation plasticity analysis of the grain size dependence of the Flow Strength of polycrystals
International Journal of Plasticity, 2008Co-Authors: D S Balint, Vikram Deshpande, A Needleman, Van Der Erik GiessenAbstract:Abstract The grain size dependence of the Flow Strength of polycrystals is analyzed using plane strain, discrete dislocation plasticity. Dislocations are modeled as line singularities in a linear elastic solid and plasticity occurs through the collective motion of large numbers of dislocations. Constitutive rules are used to model lattice resistance to dislocation motion, as well as dislocation nucleation, dislocation annihilation and the interaction with obstacles. The materials analyzed consist of micron scale grains having either one or three slip systems and two types of grain arrangements: either a checker-board pattern or randomly dispersed with a specified volume fraction. Calculations are carried out for materials with either a high density of dislocation sources or a low density of dislocation sources. In all cases, the grain boundaries are taken to be impenetrable to dislocations. A Hall–Petch type relation is predicted with Hall–Petch exponents ranging from ≈0.3 to ≈1.6 depending on the number of slip systems, the grain arrangement, the dislocation source density and the range of grain sizes to which a Hall–Petch expression is fit. The grain size dependence of the Flow Strength is obtained even when no slip incompatibility exists between grains suggesting that slip blocking/transmission governs the Hall–Petch effect in the simulations.
-
size effects in uniaxial deformation of single and polycrystals a discrete dislocation plasticity analysis
Modelling and Simulation in Materials Science and Engineering, 2006Co-Authors: D S Balint, Vikram Deshpande, A Needleman, Van Der Erik GiessenAbstract:The effect of specimen size on the uniaxial deformation response of planar single crystals and polycrystals is investigated using discrete dislocation plasticity. The dislocations are all of edge character and modelled as line singularities in a linear elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated through a set of constitutive rules. Grain boundaries are modelled as impenetrable to dislocations. Two types of polycrystalline materials are considered: one that only has grains with a single orientation while the other has a checker-board arrangement of two types of grains which are rotated 90° with respect to each other. The single crystals display a strong size dependence with the Flow Strength increasing with decreasing specimen size. In sufficiently small single crystal specimens, the nucleation rate of the dislocations is approximately equal to the rate at which the dislocations exit the specimens so that below a critical specimen size the Flow Strength is set by the Strength of the initially present Frank–Read sources. On the other hand, grain boundaries acting as barriers to plastic deformation in polycrystalline specimens of the same size lead to a more diffuse deformation pattern and to a nearly size-independent response.