Grain boundary structure in Al–Mg and Al–Mg–Sc alloys after equal-channel angular pressing

2001 ◽  
Vol 16 (2) ◽  
pp. 583-589 ◽  
Author(s):  
Keiichiro Oh-ishi ◽  
Zenji Horita ◽  
David J. Smith ◽  
Terence G. Langdon
Keyword(s):  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
High Pressure Torsion ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Boundary Structure ◽  
Angular Pressing ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Before And After

Samples of an Al–3% Mg alloy and an Al–3% Mg–0.2% Sc alloy were subjected to equal-channel angular pressing (ECAP) to reduce the grain size to approximately 0.2–0.3 μm. Some samples of each alloy were also annealed for 1 h at temperatures of either 423 or 673 K, respectively. High-resolution electron microscopy was used to examine the microstructure both before and after annealing. The grain boundaries after ECAP were wavy and faceted and in high-energy nonequilibrium configurations. These results were consistent with earlier observations of materials subjected to severe plastic deformation using high-pressure torsion. In addition, some grain boundaries in the Al–Mg–Sc alloy had a zigzag appearance after annealing at 673 K, where the straight portions of the boundary were identified as low-energy {111} planes. It is suggested these are mobile boundaries lying in a lowest energy configuration where mobility may be restricted by the presence of incoherent Al3Sc particles.

Observations of grain boundary structure in submicrometer-grained Cu and Ni using high-resolution electron microscopy

1998 ◽  
Vol 13 (2) ◽  
pp. 446-450 ◽  
Author(s):  
Zenji Horita ◽  
David J. Smith ◽  
Minoru Nemoto ◽  
Ruslan Z. Valiev ◽  
Terence G. Langdon
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Nonequilibrium State ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Typical Feature ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Resolution Electron

Submicrometer-grained (SMG) structures were produced in Cu and Ni using an intense plastic straining technique, and the grain boundaries and their vicinities were observed by high-resolution electron microscopy. The grain boundaries exhibited zigzag configurations with irregular arrangements of facets and steps, and thus they were found to be in a high-energy nonequilibrium state. A similar conclusion was reached earlier for SMG Al–Mg solid solution alloys which have much lower melting points than Cu and Ni, suggesting that nonequilibrium grain boundaries are a typical feature of metals processed by intense plastic straining.

Finding the Right Problems: Some HREM Applications to Interfaces

1984 ◽  
Vol 42 ◽  
pp. 376-379
Author(s):  
D. Cherns
Keyword(s):  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Atomic Structures ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Point To Point ◽  
The Right ◽  
New Generation ◽  
Better Than

The use of high resolution electron microscopy (HREM) to determine the atomic structure of grain boundaries and interfaces is a topic of great current interest. Grain boundary structure has been considered for many years as central to an understanding of the mechanical and transport properties of materials. Some more recent attention has focussed on the atomic structures of metalsemiconductor interfaces which are believed to control electrical properties of contacts. The atomic structures of interfaces in semiconductor or metal multilayers is an area of growing interest for understanding the unusual electrical or mechanical properties which these new materials possess. However, although the point-to-point resolutions of currently available HREMs, ∼2-3Å, appear sufficient to solve many of these problems, few atomic models of grain boundaries and interfaces have been derived. Moreover, with a new generation of 300-400kV instruments promising resolutions in the 1.6-2.0 Å range, and resolutions better than 1.5Å expected from specialist instruments, it is an appropriate time to consider the usefulness of HREM for interface studies.

Effect of Cu and Al Substitutions on the Microstructure of R-Fe-B Magnets

1991 ◽  
Vol 232 ◽  
Author(s):  
Y. J. Zhang ◽  
L. Withanawasam ◽  
G. C. Hadjipanayis ◽  
A. Kim
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Secondary Phases ◽  
Al Substitution ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Melt Spun

ABSTRACTThe coercivity of melt-spun Pr-Fe-B ribbons was found to increase with the addition of Cu and Al. The change in size and shape of grains with Cu and Al substitution were investigated by transmission eletron microscopy (TEM) and the grain boundary structure was further examined with high resolution electron microscopy (HREM). For small substitutions only “disturbed lattice” regions were observed at most of the grain boundaries. Secondary phases rich in the added elements were observed mostly at tripple grain boundaries and sometimes at grain boundaries in samples with larger amounts of substitution. The grain size in the substituted samples does not decrease much with further substitution. However, the shape of grains changes from polyhexagons to facets. The enhancement in coercivity can be explained by the grain size reduction and the modification of microstructure at the grain boundary regions.

An investigation of grain boundaries in submicrometer-grained Al-Mg solid solution alloys using high-resolution electron microscopy

1996 ◽  
Vol 11 (8) ◽  
pp. 1880-1890 ◽  
Author(s):  
Zenji Horita ◽  
David J. Smith ◽  
Minoru Furukawa ◽  
Minoru Nemoto ◽  
Ruslan Z. Valiev ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
High Resolution ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Boundary Energy ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Structural Features ◽  
Resolution Electron

High-resolution electron microscopy was used to examine the structural features of grain boundaries in Al–1.5% Mg and Al–3% Mg solid solution alloys produced with submicrometer grain sizes using an intense plastic straining technique. The grain boundaries were mostly curved or wavy along their length, and some portions were corrugated with regular or irregular arrangements of facets and steps. During exposure to high-energy electrons, grain boundary migration occurred to reduce the number of facets and thus to reduce the total boundary energy. The observed features demonstrate conclusively that the grain boundaries in these submicrometer-grained materials are in a high-energy nonequilibrium configuration.

Characterization of structural units in tilt grain boundaries

1992 ◽  
Vol 50 (1) ◽  
pp. 120-121
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Structural Units ◽  
Symmetric Tilt ◽  
Resolution Electron ◽  
Special Cases ◽  
High Resolution Electron Microscope

General tilt grain boundaries can be viewed in terms of small structural units of varying complexity. High-resolution electron microscope (HREM) images of these boundaries in many materials show this repetitive similarity of the atomic structure at the boundary plane. The structure of particular grain boundaries has been examined for several special cases and commonly observed configurations include symmetric tilt grain boundaries and asymmetric tilt grain boundaries with one grain having a prominent, low-index facet. Several different configurations of the boundary structure may possibly occur, even in the same grain boundary. There are thus many possible ways to assemble the basic structural units to form a grain boundary. These structural units and their distribution have traditionally been examined by high-resolution electron microscopy. The images of the projection of the atomic columns (or the tunnels between atomic columns) providing a template for constructing “ball-and-stick ” models of the interface.

TEM Studies of Grain Boundary Structure in a Cast Polycrystalline Silicon

2005 ◽  
Vol 475-479 ◽  
pp. 1673-1676 ◽  
Author(s):  
Isamu Kuchiwaki ◽  
Takahiro Hirabayashi ◽  
Hiroshi Fukushima
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Twin Boundary ◽  
Polycrystalline Silicon ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Resolution Electron ◽  
The Difference

Cast polycrystalline silicon for solar cell contains mostly straight twin boundaries which are thought to have little effect on the electrical activity. There are, however, some complicated grain boundaries in it. One of these boundaries consists of slightly curved and straight parts. The structure of this boundary was analyzed to investigate the difference of these two types of boundaries. The conventional transmission electron microscopy (TEM) found that this slightly curved boundary was the zigzag shaped boundary made by (11 _ ,2) and ( _ ,211) planes. High resolution electron microscopy (HREM) confirmed that (11 _ ,2) plane was the boundary of {112} Σ3 twin boundary which formed a straight grain boundary at the other end of the analyzed grain boundary, and also confirmed that ( _ ,2 11) plane was also the boundary of {112} Σ3 twin boundary which intersected with the former twin boundary at an angle of 120 [deg].

scholarly journals Effect of warm equal channel angular pressing on the structure and mechanical properties of Ti0.16Pd0.14Fe (wt%) alloy

2019 ◽  
Vol 58 (1) ◽  
pp. 22-31
Author(s):  
Victor Grishkov ◽  
Vladimir Kopylov ◽  
Alexander Lotkov ◽  
Svetlana Latushkina ◽  
Anatoly Baturin ◽  
...  
Keyword(s):  
Phase Composition ◽  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
Initial Value ◽  
Initial Strength ◽  
Torsional Strain ◽  
Angular Pressing ◽  
Initial Alloy ◽  
Average Grain Size ◽  
Before And After

Abstract Here we analyze the microstructure and phase composition of a Ti alloy with 0.16Pd and 0.14Fe (wt%) alloy exposed to warm equal channel angular pressing (ECAP) at 648 K. The analysis shows that after four ECAP passes, the material assumes a submicrocrystalline structure with an average grain size of 0.28 μm, as against its initial value 10 μm, and that the α phase dominates in the alloy both before and after ECAP. The initial alloy reveals a high content of Fe and Pd atoms near grain boundaries compared to central grain regions. Such near-boundary zones contain orthorhombic α′′ martensite in addition to the α phase, and β or α + β particles are found directly at the grain boundaries. These features of the phase composition are inherited after ECAP. The yield strength of the ECAP treated alloy is 500 MPa, being greater than the initial strength 350 MPa, and its margin of plasticity is rather high. The torsional strain up to fracture in the initial and in the ECAP treated alloy is 70% and 50%, respectively.

Correlations Between Grain Boundary Structure and Energy

1991 ◽  
Vol 229 ◽  
Author(s):  
K. L. Merkle ◽  
D. Wolf
Keyword(s):  
Electron Microscopy ◽  
Computer Simulations ◽  
Volume Expansion ◽  
Unit Area ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Simulation Results

AbstractHigh-resolution electron-microscopy (HREM) and computer simulations of <110> tilt grain boundaries (GBs) in Au are used to investigate correlations between atomic-scale GB structure and energy. The energies calculated for a variety of symmetric and asymmetric GBs suggest that asymmetric GB-plane orientations are often preferred over symmetric ones. The experimentally observed faceting behavior agrees with the computed energies. Computer simulations indicate general interrelations between GB energy and (i) volume expansion and (ii) the number of broken bonds per unit area of GB. These atomic-scale microstructural GB parameters, as evaluated from HREM observations, are compared to simulation results.

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