Grain Boundaries in Polycrystalline Ceramics

1987 ◽  
Vol 17 (1) ◽  
pp. 57-74 ◽  
Author(s):  
D R Clarke
Keyword(s):  
Grain Boundaries ◽  
Polycrystalline Ceramics

scholarly journals Properties of Na 0.5Bi0.5TiO3 and Na0.5Bi0.5 TiO3-based single crystals

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
J. Suchanicz ◽  
K. Kluczewska-Chmielarz ◽  
P. Czaja ◽  
M. Nowakowska-Malczyk ◽  
M. Was ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Single Crystals ◽  
Ferroelectric Materials ◽  
Processing Technology ◽  
Lead Free ◽  
Structural Defects ◽  
Polycrystalline Ceramics ◽  
Compositional Homogeneity ◽  
Piezoelectric Behavior

Most studies of ferroelectric materials were focused on polycrystalline ceramics. However, it is difficult to improve their properties significantly (particularly piezoelectric one) due to grain/grain boundaries, compositional homogeneity, isotropic characteristics, and structural defects. It is commonly accepted that single crystals often have better piezoelectric behavior and less structural defects than ceramics. In this paper, we provide the processing technology and properties of lead-free Na0.5Bi0.5TiO3 and Na0.5Bi0.5TiO 3-based single crystals. #FERROELECTRICS #NBT_SINGLE_CRYSTALS #FLUX_METHOD #CZOCHRALSKI_METHOD #DIELECTRIC_PROPERTIES

Migration of Silicate Liquid Out of Grain Boundaries in Ceramics

1999 ◽  
Vol 5 (S2) ◽  
pp. 800-801
Author(s):  
N. Ravishankar ◽  
C. Barry Carter
Keyword(s):  
Grain Boundaries ◽  
Strong Dependence ◽  
Liquid Phase Sintering ◽  
Laser Deposition ◽  
Intergranular Phase ◽  
Commercial Alumina ◽  
Special Boundaries ◽  
Polycrystalline Ceramics ◽  
Film Assembly ◽  
Twist Boundaries

Liquid-Phase Sintering (LPS) is a conventional fabrication route for the densification of alumina and other ceramics. The polycrystalline ceramics processed by LPS contain siliceous phases along the grain boundaries. This wetting of the grain boundaries has a strong dependence on the crystallography of the boundary. The liquid preferentially wets certain orientations while some special boundaries are ‘dry’. The mechanism of dewetting of these boundaries is not well understood. Several approaches have been adopted to study the nature of the liquid-solid interaction at the grain boundaries. In commercial alumina, anorthite is the most commonly found intergranular phase.Basal twist boundaries in alumina which contain a thin layer of anorthite glass have been investigated in the present study. Pulsed laser deposition has been used to deposit thin films of anorthite glass on optically flat basal sapphire. The substrate-film assembly is then bonded to an optically polished basal sapphire by sintering the assembly at 1650°C for 2h.

The interaction between basal-twin boundaries and a glassy phase in α-Alumina compacts

1988 ◽  
Vol 46 ◽  
pp. 570-571
Author(s):  
Yonn Kouh Simpson ◽  
C. Barry Carter
Keyword(s):  
Liquid Phase ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Glassy Phase ◽  
Liquid Phase Sintering ◽  
Boundary Mobility ◽  
Scientific Interest ◽  
Strong Anisotropy ◽  
Grain Boundary Mobility ◽  
Polycrystalline Ceramics

Understanding the nature of glass/crystalline interfaces is not only of fundamental scientific interest but is directly relevant to the liquid-phase sintering of polycrystalline ceramics such as α-alumina. Faceting behavior of alumina in the presence of SiO2 glass has been of much interest in the field of sintering with respect to the grain growth and the grain boundary mobility during sintering. The study of grain boundaries containing a glassy phase in alumina compacts is difficult however, since many of the TEM techniques presently available for the identification of a glassy phase at grain boundaries can give ambiguous results due to grain boundary grooving. A method for systematically studying glassy / crystalline interfaces without such ambiguity is therefore needed. Part of this study of the interaction of grain boundaries in alumina with an anorthite-based glassy phase is presented here.Previous systematic studies4 of different low-index surfaces of single crystal alumina showed that there is strong anisotropy in the faceting behavior of alumina and in the mobility of these facets in the presence of an anorthite-based glassy phase.

Photo-enhanced ionic conductivity across grain boundaries in polycrystalline ceramics

2022 ◽  
Author(s):  
Thomas Defferriere ◽  
Dino Klotz ◽  
Juan Carlos Gonzalez-Rosillo ◽  
Jennifer L. M. Rupp ◽  
Harry L. Tuller
Keyword(s):  
Ionic Conductivity ◽  
Grain Boundaries ◽  
Polycrystalline Ceramics

Twinning-Induced Stress Concentrations in Polycrystalline Solids

1996 ◽  
Vol 1 (1) ◽  
pp. 95-110
Author(s):  
Yongqiang Wang ◽  
Qing Jiang
Keyword(s):  
Grain Boundaries ◽  
Mechanical Twinning ◽  
External Loading ◽  
Internal Stresses ◽  
Stress Concentrations ◽  
Polycrystalline Ceramics ◽  
Polycrystalline Solids ◽  
Mechanical Twins ◽  
High Processing ◽  
Usual Formula

Polycrystalline ceramics and metals can undergo induced cracking under external loading programs or spontaneous cracking when cooled from high processing temperatures. The formation of these microcracks is often attributable to internal stresses. This analysis shows that interaction of mechanical twins with grain boundaries can result in concentrations of stress fields whose asymptotic behavior, near intersections of twinning planes with grain boundaries, corresponds to a power-law singularity. Considering that microcracks are often generated at various stages of a manufacturing process, such as annealing or quenching, the authors have studied the interaction of mechanical twinning with pre-existing microcracks, both intergranular and transgranular. Their numerical results obtained by using the material properties of α-iron and copper zirconium show that the stress field near the crack tip intersected by twinning planes exhibits a singularity of higher order than the usual [Formula: see text]-singularity. This indicates that the interaction magnifies the stress concentration and hence promotes the crack growth.

Morphology, Distribution and Identification of Micro-Constituents Along Grain Boundaries in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 176-177
Author(s):  
D. E. Fornwalt ◽  
A. R. Geary ◽  
B. H. Kear
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
Rupture Life ◽  
Stress Rupture ◽  
High Volume ◽  
Precipitate Morphology ◽  
Stress Rupture Life ◽  
Nickel Base ◽  
Scanning Electron

A systematic study has been made of the effects of various heat treatments on the microstructures of several experimental high volume fraction γ’ precipitation hardened nickel-base alloys, after doping with ∼2 w/o Hf so as to improve the stress rupture life and ductility. The most significant microstructural chan§e brought about by prolonged aging at temperatures in the range 1600°-1900°F was the decoration of grain boundaries with precipitate particles.Precipitation along the grain boundaries was first detected by optical microscopy, but it was necessary to use the scanning electron microscope to reveal the details of the precipitate morphology. Figure 1(a) shows the grain boundary precipitates in relief, after partial dissolution of the surrounding γ + γ’ matrix.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

The Effect of Specimen Thickness and Probe Size on Aem Analysis of Cr-Depletion Profiles in Sensitized Stainless Steel

1982 ◽  
Vol 40 ◽  
pp. 518-519
Author(s):  
E. L. Hall
Keyword(s):  
Grain Boundaries ◽  
Boundary Region ◽  
Chromium Concentration ◽  
Foil Thickness ◽  
Specimen Thickness ◽  
Probe Size ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Sensitization Process ◽  
Compositional Gradients

Sensitization in stainless steels is caused by the formation of chromium-rich M23C6 carbides at grain boundaries, which depletes the adjacent matrix and boundary region of chromium, and hence leads to rapid intergranular attack. To fully understand the sensitization process, and to test the accuracy of theories proposed to model this process, it is necessary to obtain very accurate measurements of the chromium concentration at grain boundaries in sensitized specimens. Quantitative X-ray spectroscopy in the analytical electron microscope (AEM) enables the chromium concentration profile across these boundaries to be studied directly; however, it has been shown that a strong effect of foil thickness and electron probe size may be present in the analysis of rapidly-changing compositional gradients. The goal of this work is to examine these effects.

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