scholarly journals Emission of Dislocations from Grain Boundaries and Its Role in Nanomaterials

Crystals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 41
Author(s):  
James C. M. Li ◽  
C. R. Feng ◽  
Bhakta B. Rath
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
Supporting Evidence ◽  
Petch Relation ◽  
Direct Observations ◽  
Transmission Electron ◽  
Alternate Mechanism

The Frank-Read model, as a way of generating dislocations in metals and alloys, is widely accepted. In the early 1960s, Li proposed an alternate mechanism. Namely, grain boundary sources for dislocations, with the aim of providing a different model for the Hall-Petch relation without the need of dislocation pile-ups at grain boundaries, or Frank-Read sources inside the grain. This article provides a review of his model, and supporting evidence for grain boundaries or interfacial sources of dislocations, including direct observations using transmission electron microscopy. The Li model has acquired new interest with the recent development of nanomaterial and multilayers. It is now known that nanocrystalline metals/alloys show a behavior different from conventional polycrystalline materials. The role of grain boundary sources in nanomaterials is reviewed briefly.

Direct Observations of Grain Boundary Phenomena during Indentation of Al and Al-Mg Thin Films

2003 ◽  
Vol 795 ◽  
Author(s):  
W. A. Soer ◽  
J. Th. M. De Hosson ◽  
A. M. Minor ◽  
E. A. Stach ◽  
J. W. Morris
Keyword(s):  
Thin Films ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Dislocation Dynamics ◽  
Direct Observations ◽  
Transmission Electron ◽  
The Matrix ◽  
Grain Boundary Motion

ABSTRACTThe deformation behavior of Al and Al-Mg thin films has been studied with the unique experimental approach of in-situ nanoindentation in a transmission electron microscope. This paper concentrates on the role of solute Mg additions in the transfer of plasticity across grain boundaries. The investigated Al alloys were deposited onto a Si substrate as thin films with a thickness of 200–300 nm and Mg concentrations of 0, 1.1, 1.8, 2.6 and 5.0 wt% Mg. The results show that in the Al-Mg alloys, the solutes effectively pin high-angle grain boundaries, while in pure Al considerable grain boundary motion is observed at room temperature. The mobility of low-angle grain boundaries is however not affected by the presence of Mg. In addition, Mg was observed to affect dislocation dynamics in the matrix.

Grain-Boundary Segregation and Phase-Separation Mechanism in Yttria-Stabilized Tetragonal Zirconia Polycrystal

2011 ◽  
Vol 484 ◽  
pp. 82-88
Author(s):  
Koji Matsui ◽  
Hidehiro Yoshida ◽  
Yuichi Ikuhara
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Cubic Phase ◽  
Phase Boundaries ◽  
Transmission Electron ◽  
Sintering Condition

Microstructure development during sintering in 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) was systematically investigated in two sintering conditions: (a) 1100-1650°C for 2 h and (b) 1300°C for 0-50 h. In the sintering condition (a), the density and grain size in Y-TZP increased with the increasing sintering temperature. Scanning transmission electron microscopy (STEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS) measurements revealed that the Y3+ ion distribution was nearly homogeneous up to 1300°C, i.e., most of grains were the tetragonal phase, but cubic-phase regions with high Y3+ ion concentration were clearly formed in grain interiors adjacent to the grain boundaries at 1500°C. High-resolution transmission electron microscopy (HRTEM) and nanoprobe EDS measurements revealed that no amorphous or second phase is present along the grain-boundary faces, and Y3+ ions segregated not only along the tetragonal-tetragonal phase boundaries but also along tetragonal-cubic phase boundaries over a width below about 10 nm, respectively. These results indicate that the cubic-phase regions are formed from the grain boundaries and/or the multiple junctions in which Y3+ ions segregated. We termed this process a “grain boundary segregation-induced phase transformation (GBSIPT)” mechanism. In the sintering condition (b), the density was low and the grain-growth rate was much slow. In the specimen sintered at 1300°C for 50 h, the cubic-phase regions were clearly formed in the grain interiors adjacent to the grain boundaries. This behavior shows that the cubic-phase regions were formed without grain growth, which can be explained by the GBSIPT model.

Grain Boundary Transformations in Bi-Doped Copper

1991 ◽  
Vol 238 ◽  
Author(s):  
Elsie C. Urdaneta ◽  
David E. Luzzi ◽  
Charles J. McMahon
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Treatment Time ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

ABSTRACTBismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.

Grain Boundary Segregation-Induced Phase Transformation and Grain Growth in Y2O3-Stabilized ZrO2 Polycrystals

2014 ◽  
Vol 616 ◽  
pp. 8-13
Author(s):  
Koji Matsui ◽  
Hidehiro Yoshida ◽  
Yuichi Ikuhara
Keyword(s):  
Electron Microscopy ◽  
Phase Transformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Boundary Segregation ◽  
Growth Behavior ◽  
Grain Boundary Segregation ◽  
Transmission Electron ◽  
Grain Growth Behavior

We systematically investigated the phase transformation and grain-growth behaviors during sintering in 2 and 3 mol% Y2O3-stabilized tetragonal ZrO2 (2Y and 3Y) and 8 mol% Y2O3-stabilized cubic ZrO2 polycrystals (8Y). In particular, grain-boundary segregation and grain-interior distribution of Y3+ ions were examined by high-resolution transmission electron microscopy (HRTEM)- and scanning transmission electron microscopy (STEM)-nanoprobe X-ray energy dispersive spectroscopy (EDS) techniques. Above 1200°C, grain growth during sintering in 8Y was much faster than that in 2Y and 3Y. In the grain boundaries in these specimens, amorphous layers did not present; however, Y3+ ions segregated at the grain boundaries over a width of about 10 nm. The amount of segregated Y3+ ions in 8Y was significantly less than in 2Y and 3Y. This indicates that the amount of segregated Y3+ ions is related to grain growth behavior; i.e., an increase in segregated Y3+ ions retards grain growth. Therefore, grain-growth behavior during sintering can be reasonably explained by the solute-drag mechanism of Y3+ ions segregating along the grain boundary. In 2Y and 3Y, the cubic-phase regions were formed in grain interiors adjacent to the grain boundaries and/or the multiple junctions in which Y3+ ions segregated, which can be explained by a grain boundary segregation-induced phase transformation (GBSIPT) mechanism.

The Role of Transmission Electron Microscopy in Characterizing the Nature and Behavior of Grain Boundaries

1971 ◽  
Vol 29 ◽  
pp. 102-103
Author(s):  
L. E. Murr
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Degrees Of Freedom ◽  
Effective Means ◽  
Average Energy ◽  
Interfacial Free Energy ◽  
Transmission Electron ◽  
And Behavior

Grain boundaries represent the single, most dominant imperfection in structural materials of engineering and industrial importance, and are a controlling factor in the strength of materials. Transmission electron microscopy, combined with the ability to gain direct crystallographic information from associated selected-area electron diffraction patterns, represents perhaps the most effective means for the investigation of the nature and behavior of grain boundaries in solids.Any segment of a grain boundary has associated with it five degrees of freedom. The electron microscope has the capability to characterize these degrees of freedom and to uniquely define the geometrical and crystallographic nature of a grain boundary. In addition, once the true geometry of intersecting grain boundaries or grain boundaries intersecting with other interfaces is determined, interfacial free energy ratios can be calculated from which the average energy associated with particular types of interfaces can be determined.

The Detection of 0.5AT% Boron in Ni3Al Using Parallel Energy Loss Spectroscopy

1990 ◽  
Vol 48 (2) ◽  
pp. 80-81
Author(s):  
C B Boothroyd ◽  
K Sato ◽  
K Yamada
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Microscope ◽  
Grain Boundary ◽  
Energy Loss ◽  
Perchloric Acid ◽  
Background Subtraction ◽  
Ethanol Solution ◽  
Transmission Electron

Recent work has suggested that the improvement in ductility when boron is added to the inherently brittle Ni3Al is caused by the segregation of boron to the grain boundaries and that this seems to be associated with the presence of disordered grain boundary “phases”. In order to clarify the role of boron at Ni3Al boundaries at the resolution of transmission electron microscopy we have developed a method for detecting concentrations as low as 0.5at% of boron in Ni3Al using parallel energy loss spectroscopy.Specimens of Ni-24at%Al with and without 0.5at% B were electropolished in a 20% perchloric acid/ethanol solution and examined at 120 kV in a Philips 420T electron microscope equipped with a Gatan parallel energy loss spectrometer. Figure la shows part of the loss spectrum from the Ni3Al-0.5%B matrix after background subtraction. Provided a high enough count rate can be obtained, the major problem for detecting small edges in energy loss spectra is channel to channel variations in the gain, which for figure la produce a noise level (2σ) of ~0.3%.

In-Plane Grain Boundary Effects on the Transport Properties of La0.7Sr0.3MnO3-δ Thin Films

1997 ◽  
Vol 494 ◽  
Author(s):  
J. Y. Gu ◽  
S. B. Ogale ◽  
K. Ghosh ◽  
T. Venkatesan ◽  
R. Ramesh ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Effects ◽  
Epitaxial Relationship ◽  
X Ray ◽  
Low Field ◽  
Grain Structures ◽  
Transmission Electron

ABSTRACTC-axis oriented La0.7Sr0.3MnO3.δ (LSMO) films were fabricated on the top of SrTiO3/YBa2Cu3O7 grown on MgO(001) substrates. From x-ray φ-scan and planar transmission electron microscopy measurements, the LSMO layer in the LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between [100] and [110] grains) in addition to the cube-on-cube epitaxial relationship. Also, epitaxial LSMO/Bi4Ti3O12/LaAl03 (001) and c-axis textured LSMO/Bi4Ti3O12/SiO2/Si(001) with random in-plane grain boundaries are introduced as the counterparts for comparison. The resistivity and magnetoresistance (MR) of LSMO layer were measured and compared in these three different heterostructures. The low field MR at low temperature shows a dramatic dependence on the nature of the grain boundary. An attempt is made to interpret these results on the basis of correlation between the magnetic properties and grain structures.

Structure of the ∑=3 (111) Grain Boundary in Cu-1.5%Sb

1992 ◽  
Vol 295 ◽  
Author(s):  
Richard W. Fonda ◽  
David E. Luzzi
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Auger Electron ◽  
Preliminary Investigation ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

AbstractGrain boundaries in quenched and aged Cu-i.5%Sb were examined with Auger electron microscopy, transmission electron microscopy, and high resolution electron microscopy. The ∑=3 grain boundaries are strongly faceted, with the facets lying primarily along the coincident (111) planes of the two grains. The grain boundaries are enriched in antimony, as demonstrated by both AES and HREM. HREM images of the ∑=3 (111) ║ (111) grain boundary differ from those of the Cu-Bi ∑ =3 (111) ║ (111) grain boundary in the lack of a significant grain boundary expansion to accommodate the excess solute at the boundary. A preliminary investigation of the atomic structure of the ∑=3 (111) ║ (111) facet by HREM and multislice calculations is presented.

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