Experimental Measurement of the Local Electronic Structure of Grain Boundaries in Ni3Al

1993 ◽  
Vol 319 ◽  
Author(s):  
D.A. Muller ◽  
P.E. Batson ◽  
S. Subramanian ◽  
S. L. Sass ◽  
J. Silcox
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Material ◽  
Local Strain ◽  
Dark Field ◽  
Hole Density ◽  
Spatially Resolved ◽  
Boron Segregation ◽  
Annular Dark Field

AbstractWe have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24 using electron energy loss spectroscopy (EELS), x-ray fluorescence (EDX) and annular dark field (ADF) imaging in a UHV STEM. A detailed study of a high angle grain boundary in nickel rich Ni3Al doped with 1000 ppm boron shows nickel enrichment occurring in a 5Å wide region. Boron segregation to the boundary is observed with EELS and is seen to vary along the boundary, coinciding with ADF contrast changes in the surrounding grains that may be due to local strain fields. Spatially resolved EELS of the Ni L2,3 core edge, which is sensitive to changes in the hole density in the nickel d band, shows boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. Boundary regions without boron have an electronic structure similar to that of the undoped grain boundaries where the Fermi level lies deeper in the nickel d band. In addition to studying boron segregation, EELS provides a unique opportunity to examine the changes in bonding that control the local properties of the material.

Local Electronic Structure and Cohesion of Grain Boundaries in Ni3Al

1994 ◽  
Vol 364 ◽  
Author(s):  
D. A. Muller ◽  
S. Subramanian ◽  
S. L. Sass ◽  
J. Silcox ◽  
P. E. Batson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Cohesive Energy ◽  
Bulk Material ◽  
Large Angle ◽  
Spatially Resolved ◽  
Boron Segregation ◽  
Environmental Embrittlement ◽  
Boron Doped ◽  
Local Electronic Structure

AbstractOne of the fundamental questions concerning Ni3Al is why doping with boron improves the room temperature ductility of the polycrystalline material. Boron is thought to prevent environmental embrittlement and increase the cohesive strength of grain boundaries since it changes the fracture mode from intergranular to transgranular. This change in cohesive energy must be reflected in the bonding changes at the grain boundary which can be probed using spatially resolved electron energy loss spectroscopy (EELS). We have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24 using EELS, EDX and ADF imaging in a UHV STEM. Ni-enrichment is seen in a 0.5–1 nm wide region at large angle grain boundaries, both in the absence and presence of B. EELS shows that B segregation can vary along the interface. The Ni L2, 3 core edge fine structure which is sensitive to the filling of the Ni d-band, shows only the boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. These results demonstrate that boron segregation increases the cohesive energy and hence improves the fracture resistance of the grain boundary, by making the bonding at boundaries similar to that in the bulk. The measured changes in d band filling may also affect the local solubility of hydrogen.

EELS Measurement of the Local Electronic Structure of Copper Atoms Segregated to Aluminum Grain Boundaries

1996 ◽  
Vol 54 ◽  
pp. 342-343
Author(s):  
S.J. Splinter ◽  
J. Bruley ◽  
P.E. Batson ◽  
D.A. Smith ◽  
R. Rosenberg
Keyword(s):  
Electronic Structure ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Thin Layers ◽  
Nominal Composition ◽  
Spatially Resolved ◽  
Service Lifetime ◽  
Heat Treated ◽  
Probe Size ◽  
Local Electronic Structure

It has long been known that the addition of Cu to Al interconnects improves the resistance to electromigration failure. It is generally accepted that this improvement is the result of Cu segregation to Al grain boundaries. The exact mechanism by which segregated Cu increases service lifetime is not understood, although it has been suggested that the formation of thin layers of θ-CuA12 (or some metastable substoichiometric precursor, θ’ or θ”) at the boundaries may be necessary. This paper reports measurements of the local electronic structure of Cu atoms segregated to Al grain boundaries using spatially resolved EELS in a UHV STEM. It is shown that segregated Cu exists in a chemical environment similar to that of Cu atoms in bulk θ-phase precipitates.Films of 100 nm thickness and nominal composition Al-2.5wt%Cu were deposited by sputtering from alloy targets onto NaCl substrates. The samples were solution heat treated at 748K for 30 min and aged at 523K for 4 h to promote equilibrium grain boundary segregation. EELS measurements were made using a Gatan 666 PEELS spectrometer interfaced to a VG HB501 STEM operating at 100 keV. The probe size was estimated to be 1 nm FWHM. Grain boundaries with the narrowest projected width were chosen for analysis. EDX measurements of Cu segregation were made using a VG HB603 STEM.

Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

2001 ◽  
Vol 7 (S2) ◽  
pp. 400-401
Author(s):  
Y. Lei ◽  
Y. Ito ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Material ◽  
Atomic Scale ◽  
Structure Property ◽  
Contrast Imaging ◽  
Structure Property Relationships ◽  
Commercial Applications ◽  
Z Contrast ◽  
Electron Energy Loss

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.

Atom-probe tomography of surface oxides and oxidized grain boundaries in alloys from nuclear reactors

2013 ◽  
Vol 1514 ◽  
pp. 107-118 ◽  
Author(s):  
Karen Kruska ◽  
David W Saxey ◽  
Takumi Terachi ◽  
Takuyo Yamada ◽  
Peter Chou ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atom Probe Tomography ◽  
Nuclear Reactors ◽  
Bulk Material ◽  
Chemical Characterization ◽  
Atom Probe ◽  
Aqueous Environment ◽  
Pressurized Water ◽  
Surface Oxides

ABSTRACTThe preparation of site-specific atom-probe tomography (APT) samples containing localized features has become possible with the use of focused ion beams (FIBs). This technique was used to achieve the analysis of surface oxides and oxidized grain boundaries in this paper. Transmission electron microscopy (TEM), providing microstructural and chemical characterization of the same features, has also been used, revealing crucial additional information.The study of grain boundary oxidation in stainless steels and nickel-based alloys is required in order to understand the mechanisms controlling stress corrosion cracking in nuclear reactors. Samples oxidized under simulated pressurized water reactor primary water conditions were used, and FIB lift-out TEM and APT specimens containing the same oxidized grain boundary were prepared and fully characterized. The results from both techniques were found fully consistent and complementary.Chromium-rich spinel oxides grew at the surface and into the bulk material, along grain boundaries. Nickel was rejected from the oxides and accumulated ahead of the oxidation front. Lithium, which was present in small quantities in the aqueous environment during oxidation, was incorporated in the oxide. All phases were accurately quantified and the effect of different experimental parameters were analysed.

Fracture Modes in Ll2 Compounds

1988 ◽  
Vol 133 ◽  
Author(s):  
C. L. Briant ◽  
A. I. Taub
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intermetallic Compounds ◽  
Boundary Segregation ◽  
Grain Boundary Segregation ◽  
Fracture Modes ◽  
Beneficial Effects ◽  
Boron Segregation ◽  
Total Composition ◽  
Carbon Additions

ABSTRACTThis paper reports a study of grain boundary segregation and fracture modes in Ll2 intermetallic compounds. Data obtained on Ni3A1, Ni3Si, Ni3Ga, Ni3Ge, and Pt3Ga will be presented. It will be shown that the amount of boron segregation and its ability to improve cohesion depends on the total composition of the compound. The beneficial effects of boron can be counteracted by the presence of borides on the grain boundaries. Carbon additions also produce some improvement in ductility in Ni3Si.

An atom probe field ion microscope analysis of grain boundary chemistry in boron and carbon doped NiAl

1992 ◽  
Vol 50 (2) ◽  
pp. 1220-1221
Author(s):  
Raman Jayaram ◽  
M.K Miller
Keyword(s):  
Grain Boundary ◽  
Enrichment Factor ◽  
Grain Boundaries ◽  
Atom Probe ◽  
Probe Field ◽  
Carbon Doped ◽  
Boron Segregation ◽  
Microanalytical Technique ◽  
Microalloying Elements ◽  
Boundary Chemistry

The low temperature brittleness of nickel aluminides has been a serious impediment to their technological applications. A commonly employed technique to ductilize these materials involves the addition of suitable microalloying elements and correlating grain boundary chemistry with fracture mode. In the well documented case of Ni3Al, boron segregation to grain boundaries is accompanied by suppression of intergranular fracture and a significant increase in ductility. The high resolution microanalytical technique of atom probe field ion microscopy (APFIM) has been used in this study to analyze grain boundaries in order to characterize similar attempts to ductilize NiAl. APFIM specimens were prepared from tensile specimens of stoichiometric NiAl doped with either 0.04 or 0.12 at. % boron or 0.1 at % carbon, respectively. A field ion image of a grain boundary in a B-doped NiAl specimen is shown in Fig. 1. The brightly-imaging spots decorating the boundary were determined by atom probe analysis to be boron atoms. The boron enrichment factor at the boundary depends on the assumed thickness of the segregation as shown in Fig. 2 with an enrichment factor of ∼850 times for a monolayer coverage (i.e. 0.2 nm).

Elemental Analysis of Matrix Grain Boundaries in Sic Whisker Reinforced Si3N4 Based Composites

1992 ◽  
Vol 287 ◽  
Author(s):  
J. Liu ◽  
K. Das Chowdhury ◽  
R. W. Carpenter ◽  
W. Braue
Keyword(s):  
Grain Boundaries ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Light Element ◽  
Ceramic Matrix Composites ◽  
High Resolution Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Scanning Transmission ◽  
Annular Dark Field

ABSTRACTThe structures of SiC/Si3N4 interfaces and Si3N4 matrix grain boundaries in Ceramic Matrix Composites (CMC) were investigated by high resolution electron microscopy. The light element chemistry of the interfaces was analyzed by high spatial resolution (∼3 nm) position resolved EELS in a field emission TEM and by high spatial resolution EDS in a dedicated scanning transmission electron microscope (STEM). High-angle annular dark-field (HAADF) imaging (resolution < 1 nm) technique was used to determine the distribution of yttrium atoms at matrix grain boundaries and at SiC/Si3N4 interfaces. HAADF images suggest that yttrium might diffuse into Si3N4 crystals bounding the interfacial and grain boundary regions.

Investigations of the Bonding Changes Associated with Grain Boundary Embrittlement

1996 ◽  
Vol 458 ◽  
Author(s):  
V. J. Keast ◽  
J. Bruley ◽  
D. B. Williams
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Edge Structure ◽  
Grain Boundary Embrittlement ◽  
Impurity Elements ◽  
Electron Energy Loss ◽  
Segregation Of Impurities ◽  
Boundary Embrittlement

ABSTRACTThe embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.

scholarly journals The Electronic Structure of Grain Boundaries in NB

1990 ◽  
Vol 209 ◽  
Author(s):  
Erik C. Sowa ◽  
A. Gonis ◽  
X. -G. Zhang
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Multiple Scattering ◽  
First Principles ◽  
Scattering Theory ◽  
Real Space ◽  
First Principles Calculations ◽  
Densities Of States ◽  
Local Densities

ABSTRACTWe present first-principles calculations of the electronic structure of Nb grain boundaries. These are the first such calculations for a bcc metal using the real-space multiple-scattering theory (RSMST). Local densities of states near a Σ5 twist grain boundary are compared to those for bulk Nb.

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