The Effect of Y and Zr on the Oxidation of NiA1

1994 ◽  
Vol 364 ◽  
Author(s):  
Eckart Schumann ◽  
J. C. Yang ◽  
M. Rühle ◽  
M. J. Graham
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Metal Oxide ◽  
Grain Boundaries ◽  
Oxidation Behaviour ◽  
Oxide Interface ◽  
Analytical Tem ◽  
Outward Transport ◽  
Tracer Experiments

AbstractThe effect of Y and Zr on the oxidation behaviour of NiAl has been investigated using high resolution SIMS and analytical TEM. 18O tracer experiments in conjunction with SIMS showed that Y and Zr reduce the outward transport of cations during the growth of the AI2O3 scale. Complementary STEM-EDS measurements revealed segregation of Y and Zr at the metal/oxide interface as well as the grain boundaries in the AI2O3 scale. The amounts of segregation at both the interface and grain boundary were calculated to be less than one monolayer.

Mechanisms of Oxidation of Fuel Cladding Alloys Revealed by High Resolution APT, TEM and SIMS Analysis

2012 ◽  
Vol 1383 ◽  
Author(s):  
Chris R. M. Grovenor ◽  
Na Ni ◽  
Daniel Hudson ◽  
Sean S. Yardley ◽  
Katie L. Moore ◽  
...  
Keyword(s):  
High Resolution ◽  
Metal Oxide ◽  
Oxide Layer ◽  
Electrochemical Impedance ◽  
Complex Structure ◽  
Oxygen Stoichiometry ◽  
Aqueous Environment ◽  
Oxide Interface ◽  
Aqueous Corrosion ◽  
Sims Analysis

ABSTRACTAqueous corrosion of zirconium alloys has become the major factor limiting prolonged fuel campaigns in nuclear plant. Studies using SEM, TEM and electrochemical impedance measurements have been interpreted as showing a dense inner-most oxide layer, and an increased thickness of the layer has been correlated to a better corrosion resistance. Many authors have reported that an ‘intermediate layer’ at the metal oxide interface has a complex structure or/and stochiometry different to that of both the bulk oxide and bulk metal, sometimes claimed to be a suboxide phase. Diffraction evidence has suggested the presence of both cubic ZrO and rhombohedral Zr3O phases, and compositional analysis has revealed similar variations in local oxygen stoichiometry.We have carried out a systematic investigation of the structure and chemistry of the metal/oxide interface in samples of commercial ZIRLO corroded for times up to 180 days. We have developed new experimental techniques for the study of these interfaces both by Electron Energy Loss Spectroscopy (EELS) analysis in the Transmission Electron Microscope (TEM) and by Atom Probe Tomography (APT), and exactly the same samples have been investigated by both techniques. Our results show the development of a clearly defined suboxide layer of stoichiometry close to ZrO, and the subsequent disappearance of this layer at the first of the characteristic ‘breakaway’ transitions in the oxidation kinetics. We can correlate this behaviour with changes in the structure of the oxide layer, and particularly the development of interconnected porosity that links the corroding interface with the aqueous environment. Using high resolution SIMS analysis of isotopically spiked samples we demonstrate the penetration of the oxidising species through these porous outer oxide layers.

Analytical Electron Microscopy And High-Resolution Electron Microscopy Studies Of Grain-Boundary Films In Silicon Nitride-Based Ceramics

1991 ◽  
Vol 238 ◽  
Author(s):  
H.-J. Kleebe ◽  
M. Rühle
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Film Thickness ◽  
Grain Boundaries ◽  
Liquid Phase Sintering ◽  
Chemical Compositions ◽  
Phase Boundaries ◽  
Intergranular Films ◽  
Boundary Films

ABSTRACTThe microstructures of post-sintered reaction-bonded Si3N4 materials (SRBSN) were investigated. The materials consist of large elongated β-Si3N4 grains embedded in a finegrained matrix. Amorphous secondary phases exist at triple grain junctions owing to the liquid phase sintering involved during densificacition. Those amorphous phases can be crystallized (nearly completely) by post-sintering heat treatment. Apart from these crystalline grain pockets the grains of all materials are covered with thin (<l-2 nm) amorphous intergranular films on both Si3N4/Si3N4 grain boundaries as well as on secondary-phase/Si3N4 phase boundaries. A control of the intergranular films is most desirable since they limit the high-temperature mechanical properties of Si3N4-based ceramics. Therefore, the required characterization was performed by analytical and high-resolution transmission electron microscopy (AEM/HREM). Si3N4 materials with different rare-earth and transition-element oxide additions were studied. AEM and HREM investigations revealed marked differences in thicknesses and chemical compositions of the different intergranular films depending on the system analyzed indicating a strong dependence of film thickness on chemical composition. However, a given composition of each investigated material showed a characteristic intergranular film thickness, independent of grain misorientation, with the only exception of low-energy grain boundaries. The thickness of the intergranular films was constant within 0.2 nm. In addition, the film thickness of phase boundaries was always greater (by 1–2 nm) compared to grain-boundary films.

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.

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.

High-resolution imaging of symmetric tilt and mixed character boundaries in Al

1990 ◽  
Vol 48 (4) ◽  
pp. 336-337
Author(s):  
M. Shamzuzzoha ◽  
P.A. Deymier ◽  
David J. Smith
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Thin Foil ◽  
Polycrystalline Materials ◽  
Voltage Electron ◽  
Symmetric Tilt ◽  
Resolution Electron ◽  
Resolution Imaging ◽  
Electron Microscopes

The determination of the core structure of grain boundaries is central to a better understanding of the properties of polycrystalline materials. With the recent advent of intermediate-voltage electron microscopes (300-400kV), it is possible to obtain atomic-resolution images of grain boundaries in many metals - for example, the atomic structure of periodic grain boundaries in selected metals has been studied. Our knowledge of materials properties can be further enhanced by investigating more complex, arbitrarily misoriented grain boundaries. In this paper, we will report HREM imaging of a symmetric tilt low-angle grain boundary and a twist-and-tilt (mixed character) grain boundary in Al.The Al bicrystals used in this study were produced by cross-rolling and annealing methods described in detail elsewhere. Thin foil specimens of 3mm diameter containing specific boundaries were obtained by spark-cutting and subsequent electropolishing in 73% methanol, 25% nitric acid and 2% hydrochloric acid. HREM was performed with a JEM-4000EX operated at 400kV, using axial illumination and without an objective aperture. High-resolution electron micrographs were recorded near the optimum defocus, typically at a magnification of 500,000 times.

Void Formation and Filling under Alumina Scales Formed on Fe-20Cr-5Al Alloy Thin Foils

2008 ◽  
Vol 595-598 ◽  
pp. 1093-1101 ◽  
Author(s):  
D.J. Potter ◽  
G.J. Tatlock
Keyword(s):  
Metal Oxide ◽  
Void Formation ◽  
Thin Foil ◽  
Alumina Scale ◽  
Oxidation Behaviour ◽  
Sustainable Growth ◽  
Aluminium Content ◽  
Oxide Interface ◽  
Thin Foils ◽  
Electron Microscopes

The oxidation behaviour and the subsequent chemical failure of a Fe-20Cr-5Al based alloy were studied at 1200°C in laboratory air, at times of up to 700 hours. Tests on 70 micron thick foils, showed void formation at the metal/oxide interface soon after the aluminium content in the alloy dropped below a critical level (≤0.5 wt%). At this stage, the alloy could no longer sustain alumina scale formation and resulted in the initiation and development of a Cr-rich sub-layer. This chromia layer was found to be continuous and of a uniform thickness. As the sub-layer formed, voids were also observed at the metal/oxide interface. The voids were found to fill with chromia after further exposure. It is thought that the change in oxide growth mechanism from alumina to chromia growth is responsible for the void formation. This also explains the lack of void formation during the sustainable growth of the alumina scale. The introduction of silicon to the Fe-20Cr-5Al based alloy via a diffusion couple was found to significantly influence the oxidation behaviour of the thin foils. Void formation was observed directly beneath the alumina scale and filled voids were now found to contain silicon oxide rather than chromia. The void filling mechanism also appeared to be different. With chromia filled voids, the filling commenced from the underside of the oxide, with the oxide growing inwards, while silica containing voids were filled by silica growing outwards into the void from the substrate. Throughout the study, optical and scanning electron microscopes were used to analyse all stages of oxidation and the subsequent failure of the thin foil samples. EBSD was also used to generate a more comprehensive analysis of selected locations.

Z-Contrast Imaging of Grain-Boundary Core Structures in Semiconductors

MRS Bulletin ◽  
1997 ◽  
Vol 22 (8) ◽  
pp. 53-57 ◽  
Author(s):  
M.F. Chisholm ◽  
S.J. Pennycook
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Phase Contrast ◽  
Atomic Scale ◽  
Resolving Power ◽  
Boundary Structure ◽  
Contrast Imaging ◽  
Contrast Technique ◽  
Z Contrast

Interest in semiconductor grain boundaries relates to the development of polycrystalline materials for photovoltaics and integrated-circuit interconnects. Although these structures are responsible for deleterious electrical effects, there are few experimental techniques available to study them at the required atomic scale. Therefore models of the physical processes occurring at grain boundaries have necessarily taken a macroscopic approach. Fortunately recent developments have resulted in tools that provide unprecedented glimpses into these interfaces and that will allow us to address anew the connection between grain-boundary structure and properties.Z-Contrast ImagingWhen exploring the unknown, we rely heavily on our eyes (incoherent imaging) to provide a direct image of a new object. In order to explore the unforeseen atomic configurations present at extended defects in materials, it again would be desirable if one could obtain a directly interpretable image of the unfamiliar structures present in the defect cores. Z-contrast electron microscopy provides such a view with both atomic resolution and compositional sensitivity.This high-resolution imaging technique differs from conventional high-resolution phase-contrast imaging. The phase-contrast technique produces a coherent image, an interference pattern formed by recombining the waves diffracted by the specimen. In the Z-contrast technique, the image is incoherent; it is essentially a map of the scattering power of the specimen. Additionally as was first determined by Lord Rayleigh, the incoherent mode of image formation has double the resolving power of the coherent mode.

Possible evidence for overcoordination at semiconductor grain boundaries

1990 ◽  
Vol 5 (3) ◽  
pp. 587-592 ◽  
Author(s):  
W. Krakow ◽  
A. A. Levi ◽  
S. T. Pantelides
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Experimental Evidence ◽  
Screw Dislocation ◽  
Electron Micrograph ◽  
Resolution Electron ◽  
Tilt Grain Boundary

The structure of a near coincidence Ge tilt grain boundary, containing a step, has been derived from a high resolution electron micrograph. There are two possible interpretations of portions of this interface, one of which is the existence of a sheet of fivefold coordinated atoms between the Σ = 19 and Σ = 27 coincidence misorientations. This finding may represent the first experimental evidence that overcoordinated atoms are present at semiconductor grain boundaries free of a screw dislocation.

A Tem Investigation of Secondary Dislocations in Grain Boundaries in Germanium

1989 ◽  
Vol 163 ◽  
Author(s):  
M. Griss ◽  
M. Seibt ◽  
H.J. Möller
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Low Energy ◽  
Dislocation Network ◽  
Tilt Axis ◽  
Secondary Dislocation ◽  
Tilt Grain Boundary

AbstractGermanium bicrystals containing dissociated low energy grain boundaries with a common [011] tilt axis were studied. The dislocation structure of a grain boundary with a misorientation of about 28° has been investigated in detail and could be interpreted as a near-coincidence Σ 27 - tilt grain boundary. Both conventional and high-resolution techniques were applied to analyze the Burgers vectors of the secondary dislocation network. In all cases non - primitive Burgers vectors were observed. The comparison with previous results indicates that the Burgers vectors of the dislocation network may depend on the degree of misorientation of the bicrystal.

Sign in / Sign up

Export Citation Format

Share Document