scholarly journals Texture and Microstructure Development in Al2O3-Platelet Reinforced Ce-ZrO2/Al2O3 Laminates Produced by Centrifugal Consolidation

1995 ◽  
Vol 24 (1-3) ◽  
pp. 43-52 ◽  
Author(s):  
Ryan K. Roeder ◽  
Keith J. Bowman ◽  
Kevin P. Trumble
Keyword(s):  
Microstructural Evolution ◽  
Volume Fraction ◽  
Phase Segregation ◽  
Functionally Gradient ◽  
Property Evaluation ◽  
Quantitative Image ◽  
Microstructural Design ◽  
Efficient Packing ◽  
And Control ◽  
Platelet Content

A dispersed, low-solids-fraction suspension containing Ce-ZrO2, fine Al2O3 and 5 vol% Al2O3-platelets was segregated using centrifugal consolidation to produce functionally gradient laminates (FGLs). Platelet alignment facilitated efficient packing of highly anisometric platelets to high densities. The complexity and anisotropy of the microstructure warrants a quantitative analysis of the microstructural evolution prior to any property evaluation. Quantitative image analysis was used to examine changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets with sintering time. In all cases, special attention was given to the effects of texture during microstructural evolution. Platelet alignment enhanced densification via anisotropic shrinkage, overcoming constraint that otherwise inhibits densification in platelet-containing materials. Also, platelet alignment and microstructural design were used to initiate and control anisotropic grain growth. Platelet growth (at the expense of smaller particles of the same phase) during annealing promoted further phase segregation and produced higher platelet content composites consisting of larger platelets, without having to consolidate high contents of large platelets.

scholarly journals A magnetic resonance study of temperature-dependent microstructural evolution and self-diffusion of water in Arctic first-year sea ice

2005 ◽  
Vol 40 ◽  
pp. 179-184 ◽  
Author(s):  
C. Bock ◽  
H. Eicken
Keyword(s):  
Magnetic Resonance ◽  
Sea Ice ◽  
Microstructural Evolution ◽  
Volume Fraction ◽  
Bulk Liquid ◽  
Liquid Volume ◽  
Liquid Volume Fraction ◽  
Cross Sectional ◽  
Pore Connectivity ◽  
Pore Number

AbstractThe microstructural evolution of brine inclusions in granular and columnar sea ice has been investigated through magnetic resonance imaging (MRI) for temperatures between –28 and –3˚C. Thin-section and salinity measurements were completed on core samples obtained from winter sea ice near Barrow, Alaska, USA. Subsamples of granular (2–5cm depth in core) and columnar sea ice (20–23 cm depth) were investigated with morphological spin-echo and diffusion-weighted imaging in a Bruker 4.7T MRI system operating at field gradients of 200 mTm–1 at temperatures of approximately –28, –15, –6 and –3˚C. Average linear pore dimensions range from 0.2 to 1 mm and increase with bulk liquid volume fraction as temperatures rise from –15 to –3˚C. Granular ice pores are significantly larger than columnar ice pores and exhibit a higher degree of connectivity. No evidence is found of strongly non-linear increases in pore connectivity based on the MRI data. This might be explained by shortcomings in resolution, sensitivity and lack of truly three-dimensional data, differences between laboratory and field conditions or the absence of a percolation transition. Pore connectivity increases between –6 and –3˚C. Pore-number densities average at 1.4±1.2mm–2. The pore-number density distribution as a function of cross-sectional area conforms with power-law and lognormal distributions previously identified, although significant variations occur as a function of ice type and temperature. At low temperatures (< –26˚C), pore sizes were estimated from 1H self-diffusivity measurements, with self-diffusivity lower by up to an order of magnitude than in the free liquid. Analysis of diffusional length scales suggests characteristic pore dimensions of <1 μm at < –26˚C.

scholarly journals Effects of vertebroplasty on endplate subsidence in elderly female spines

2015 ◽  
Vol 22 (3) ◽  
pp. 273-282 ◽  
Author(s):  
Srinidhi Nagaraja ◽  
Hassan K. Awada ◽  
Maureen L. Dreher ◽  
John T. Bouck ◽  
Shikha Gupta
Keyword(s):  
Bone Cement ◽  
Trabecular Bone ◽  
Volume Fraction ◽  
Micro Ct ◽  
Control Groups ◽  
Bone Volume Fraction ◽  
Elderly Female ◽  
Maximum Subsidence ◽  
And Control ◽  
Adjacent Vertebra

OBJECT The aim in this study was to quantify the effects of vertebroplasty on endplate subsidence in treated and adjacent vertebrae and their relationship to endplate thickness and underlying trabecular bone in elderly female spines. METHODS Vertebral compression fractures were created in female cadaveric (age range 51–88 years) thoracolumbar spine segments. Specimens were placed into either the control or vertebroplasty group (n = 9/group) such that bone mineral density, trabecular microarchitecture, and age were statistically similar between groups. For the vertebroplasty group, polymethylmethacrylate bone cement was injected into the fractured vertebral body under fluoroscopy. Cyclic compression (685–1370 N sinusoid) was performed on all spine segments for 115,000 cycles. Micro-CT scans were obtained before and after cyclic loading to quantify endplate subsidence. Maximum subsidence was compared between groups in the caudal endplate of the superior adjacent vertebra (SVcau); cranial (TVcra) and caudal (TVcau) endplates of the treated vertebra; and the cranial endplate of the inferior adjacent vertebra (IVcra). In addition, micro-CT images were used to quantify average endplate thickness and trabecular bone volume fraction. These parameters were then correlated with maximum endplate subsidence for each endplate. RESULTS The maximum subsidence in SVcau endplate for the vertebroplasty group (0.34 ± 0.58 mm) was significantly (p < 0.05) greater than for the control group (−0.13 ± 0.27 mm). Maximum subsidence in the TVcra, TVcau, and IVcra endplates were greater in the vertebroplasty group, but these differences were not significant (p > 0.16). Increased subsidence in the vertebroplasty group manifested locally in the anterior region of the SVcau endplate and in the posterior region of the TVcra and TVcau endplates (p < 0.10). Increased subsidence was observed in thinner endplates with lower trabecular bone volume fraction for both vertebroplasty and control groups (R2 correlation up to 62%). In the SVcau endplate specifically, these 2 covariates aided in understanding subsidence differences between vertebroplasty and control groups. CONCLUSIONS Bone cement injected during vertebroplasty alters local biomechanics in elderly female spines, resulting in increased endplate disruption in treated and superior adjacent vertebrae. More specifically, bone cement increases subsidence in the posterior regions of the treated endplates and the anterior region of the superior caudal endplate. This increased subsidence may be the initial mechanism leading to subsequent compression fractures after vertebroplasty, particularly in vertebrae superior to the treated level.

Microstructural Changes of a Creep-Damaged Nickel-Based K002 Superalloy Containing Hf Element under Different HIP Temperatures

2016 ◽  
Vol 35 (2) ◽  
pp. 153-159 ◽  
Author(s):  
Xiaomeng Wang ◽  
Yu Zhou ◽  
Jian Dong ◽  
Tianyou Wang ◽  
Zihua Zhao ◽  
...  
Keyword(s):  
Microstructural Evolution ◽  
Temperature Increase ◽  
Volume Fraction ◽  
Hot Isostatic Pressing ◽  
Nucleation And Growth ◽  
Dissolution Process ◽  
Microstructural Changes ◽  
Isostatic Pressing ◽  
Solute Atoms

AbstractEffects of hot isostatic pressing (HIP) temperature on the microstructural evolution of a nickel-based K002 superalloy containing Hf element after long-term service were investigated using three different soaking temperatures during HIP. The degraded γ′ precipitates represented coarse and irregular morphology after long-term service. These γ′ precipitates still were of coarse and irregular shape, but the size and volume fraction of γ′ precipitates were markedly reduced under HIP condition of 1,190°C/200 MPa/4 h, indicating that the γ′ precipitates were experiencing a dissolution process. Meanwhile, the concentrically oriented N-type γ′ rafting structure around the cavities was formed. With HIP temperature increase to 1,220°C and 1,250°C, the small-sized, cubic and regular γ′ precipitates were re-precipitated, and the concentrically oriented γ′ structure vanished. The unstable morphology induced by the nucleation and growth of γ matrix was found near the creep cavities, indicating that the solute atoms diffused inward the creep-induced cavities during HIP. However, at HIP temperature of 1,220°C and 1,250°C, a large number of blocky MC(2)-type carbides containing amounts of Hf elements were precipitated, demonstrating that HIP treatment at higher temperatures can result in the formation of a large number of blocky MC(2)-type carbides.

Microstructural Evolution of Al–Zn–Mg–Cu Alloys in Accordance with Homogenization Time

2020 ◽  
Vol 20 (11) ◽  
pp. 6890-6896
Author(s):  
Woojin An ◽  
Jaewon Heo ◽  
Dongchan Jang ◽  
Kwang Jun Euh ◽  
Im Doo Jung ◽  
...  
Keyword(s):  
Microstructural Evolution ◽  
Focused Ion Beam ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Ion Beam ◽  
Homogenization Temperature ◽  
Strain Burst ◽  
Cu Alloys ◽  
Homogenization Time ◽  
Backscatter Diffraction

The microstructural evolution of Al–Zn–Mg–Cu alloys has been investigated for the homogenization time effect on the texture, grain orientation and dislocation density. The Al–Zn–Mg–Cu alloys were casted and homogenized for 4, 8, 16 and 24 hours. Electron backscatter diffraction (EBSD) analysis was conducted to characterize the microstructural behavior. Micropillars were fabricated using focused ion beam (FIB) milling in grains of specific crystallographic orientations. Coarse precipitations in the grain boundaries are S (Al2CuMg) and T (Al2Mg3Zn3) phases verified by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) observation. With increasing homogenization time, equiaxed cell sizes increased. The volume fraction of S and T phases decreased with the diffusion of atomic elements into matrix. The Vickers hardness and tensile strength values decreased with homogenization temperature. The micropillar compression analysis was compared to macro tensile test results to understand the size effect and strain burst phenomenon on the mechanical properties of Al–Zn–Mg–Cu alloys.

Hot Deformation Behavior and Microstructural Evolution of Mg-Nd-Zn-Zr Magnesium Alloy

2013 ◽  
Vol 747-748 ◽  
pp. 320-326 ◽  
Author(s):  
Wen Xiang Wu ◽  
Li Jin ◽  
Jie Dong ◽  
Zhen Yan Zhang ◽  
Wen Jiang Ding
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Hot Deformation ◽  
Fine Particles ◽  
Volume Fraction ◽  
Strain Rate Range ◽  
Compression Tests ◽  
Average Size

The hot deformation behaviors and microstructural evolution of Mg-3.0Nd-0.2Zn-0.4Zr (wt. %, NZ30K) alloy were investigated by means of the isothermal hot compression tests at temperatures of 350-500 °C with strain rates of 0.001, 0.01, 0.1 and 1s-1. The results showed that the flow stress increased to a peak and then decreased which showed a dynamic flow softening. The flow stress behavior was described by the hyperbolic sine constitutive equation with an average activation energy of 193.8 kJ/mol. The average size of dynamically recrystallized grains of hot deformed NZ30K alloy was reduced by increasing the strain rate and/or decreasing the deformation temperature. A large amount of fine particles precipitated in the grains interior and at the grain boundaries when heated to the compression temperatures and soaked for 5min below 450 °C. However, the volume fraction of particles decreased significantly when soaked for 5 min at 500 °C, and the coarse particles precipitated mainly at the grain boundaries. Hot deformation at the temperature of 500 °C around and at the strain rate range of 0.1s-1 was desirable for NZ30K alloy.

Re-Meshing in Finite Element Simulations of Hot Working Including a Microstructural Evolution Model

2014 ◽  
Vol 611-612 ◽  
pp. 505-512
Author(s):  
Markus Bambach
Keyword(s):  
Finite Element ◽  
Microstructural Evolution ◽  
Volume Fraction ◽  
Substantial Reduction ◽  
Large Error ◽  
Hot Working ◽  
Data Mapping ◽  
Element Mesh ◽  
Standard Data ◽  
Least Squares Fit

Material models that couple the evolution of flow stress to the evolution of the microstructure are important for the simulation of hot working processes in which the microstructure undergoes large changes. Among the microstructural evolution mechanisms in hot working, dynamic recrystallization (DRX) plays a central role as it occurs during deformation. When the workpiece deforms, the element shape may deteriorate, which makes re-meshing necessary. At the same time, certain regions of the finite element mesh undergo DRX and a sharp interface between recrystallized and non-recrystallized portions of the workpiece develops. Elements of the old mesh that are cut by the interface contain nodes with a non-zero recrystallized volume fraction and nodes where the recrystallized volume fraction is zero. During re-meshing, when the microstructural data is transferred to the new mesh, nodes or integration points that are actually in region of the workpiece that is not yet recrystallized may be assigned a non-zero recrystallized volume fraction. As a consequence, the interface moves, which is unwanted and may produce large errors when re-meshing is frequently done. In this paper, the problem of the propagation of the DRX interface during re-meshing is treated. It is shown that the propagation occurs with standard data mapping algorithms and produces a large error at the interface. A re-meshing scheme is proposed that uses a smooth mesh-free interpolating function based on radial basis functions to interpolate the recrystallized volume fraction. The interface is the zero level set of this interpolant. Performing the mapping as a least squares fit of the interpolant allows for a substantial reduction of the mapping error and suppresses the propagation of the DRX front.

Analysis on the Residual Stresses in Functionally Gradient Fe360/Glass-Ceramic Coatings

2013 ◽  
Vol 717 ◽  
pp. 215-220
Author(s):  
Li Ming Zhou ◽  
Wei Gong ◽  
En Ze Wang
Keyword(s):  
Residual Stress ◽  
Glass Ceramic ◽  
Volume Fraction ◽  
Geometric Model ◽  
Low Carbon Steel ◽  
Ceramic Coatings ◽  
Low Carbon ◽  
Element Analysis ◽  
Functionally Gradient ◽  
Gradient Coatings

A novel functionally gradient composite was reported in this article. The composite material are composed of plain low carbon steel Fe360 as a substrate and glass-ceramics containing ZrO2 reinforcing particles as a coating. Based on a mathematical model of the residual stress, the geometric model and finite element analysis models of the Fe360/glass-ceramic gradient coatings were established. The residual stress of the gradient layers was calculated with the commercial software ANSYS 10.0. The results showed that the differences of thermal expansion coefficient and shrinkage rate in each layer resulting from the difference of the volume fraction of ZrO2 in each gradient layer could make the surface layer generate suitable compressive stress. The maximum residual stress presents itself at the interface between the substrate and the gradient coatings. The layer numbers and the thickness of graded coatings have a significant effect on the residual stress.

Segregation Measurement of Inconel 718 Feedstocks Used in Low-Pressure Metal Injection Molding

2016 ◽  
Vol 857 ◽  
pp. 286-290 ◽  
Author(s):  
Faoud Fareh ◽  
V. Demers ◽  
S. Turenne ◽  
O. Scalzo
Keyword(s):  
Injection Molding ◽  
Inconel 718 ◽  
Volume Fraction ◽  
Phase Segregation ◽  
Ethylene Vinyl Acetate ◽  
Low Pressure ◽  
Paraffin Wax ◽  
Metal Injection Molding ◽  
Solid Loading ◽  
Molten State

Low-pressure metal injection molding (LP-MIM) is an advanced manufacturing technology where a wax-based feedstock is injected into a complex shape before densification heat treatments. Feedstock is generally designed to minimize segregation, maximize flowability, maximize the strength of the molded component, maximize the solid loading potential and ease of debinding. In this study, the emphasis is placed on the evaluation of the effect of segregation on different wax-based Inconel 718 superalloy feedstocks used in LP-MIM. In powder metallurgy, particle or phase segregation generates a fluctuation of the particle distribution in powder-binder mixtures from point to point. Such demixing generally occurs before or during the injection process, and can lead to the formation of defects such as cracks, distortions or heterogeneous shrinkage of the sintered parts. Different wax-based feedstocks were poured in cylindrical hot molds (95°C), maintained in molten state for 1 minutes or for 60 minutes, and rapidly cooled to room temperature. The specimens were then extracted from the top and bottom regions of each cylindrical part. A thermogravimetric analysis technique was used to measure the volume fraction of powder at these two locations in order to quantify the degree of segregation in green parts. The best candidate feedstocks minimizing segregation are the mixtures containing only paraffin wax, or those containing paraffin wax and ethylene vinyl acetate combined. An increase in the time spent in the molten state and the use of beeswax or stearic acid promote the powder-binder separation of feedstocks.

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