55 research outputs found
Nanocrystalline Zr3Al Made through Amorphization by Repeated Cold Rolling and Followed by Crystallization
The intermetallic compound Zr3Al is severely deformed by the method of
repeated cold rolling. By X-ray diffraction it is shown that this leads to
amorphization. TEM investigations reveal that a homogeneously distributed
debris of very small nanocrystals is present in the amorphous matrix that is
not resolved by X-ray diffraction. After heating to 773 K, the crystallization
of the amorphous structure leads to a fully nanocrystalline structure of small
grains (10 - 20 nm in diameter) of the non-equilibrium Zr2Al phase. It is
concluded that the debris retained in the amorphous phase acts as nuclei. After
heating to 973 K the grains grow to about 100 nm in diameter and the compound
Zr3Al starts to form, that is corresponding to the alloy composition
High pressure torsion of nickel powders obtained by electrodeposition
A new synthesis route for the production of bulk nanostructured materials is presented.
Fine Ni powder was made by selected appropriate electrolysis conditions. A
compact material with an average grain size below 40 nm was obtained by subsequent
cold pressing. Then, using the high pressure torsion (HPT) deformation technique dense
bulk nanocrystalline Ni was achieved. The detailed structural investigations of the asprepared
and HPT deformed Ni powder, including X-ray diffraction (XRD) and transmission
electron microscopy (TEM), reveal in both cases the presence of a face centered
cubic (FCC) phase without presence of any oxides. Coherently scattering domain size
measurements by XRD show a value of 24 nm for the as-deposited powder and an even
smaller value of 13.5 nm after HPT deformation. In addition, optical emission spectroscopy
was employed to determine the impurity content of the obtained nanostructured
material, showing a relatively low content of 0.9 % carbon and oxygen. The microhardness
increased after deformation from (1.5 ± 0.08) GPa for the as-deposited Ni powder
to (6.6 ± 0.2) GPa for the HPT deformed Ni powder.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2061
Giant crystals inside mitochondria of equine chondrocytes
The present study reports for the first time the presence of giant crystals in mitochondria of equine chondrocytes. These structures show dark contrast in TEM images as well as a granular substructure of regularly aligned 12 nm small units. Different zone axes of the crystalline structure were analysed by means of Fourier transformation of lattice-resolution TEM images proving the crystalline nature of the structure. Elemental analysis reveals a high content of nitrogen referring to protein. The outer shape of the crystals is geometrical with an up to hexagonal profile in cross sections. It is elongated, spanning a length of several micrometres through the whole cell. In some chondrocytes, several crystals were found, sometimes combined in a single mitochondrion. Crystals were preferentially aligned along the long axis of the cells, thus appearing in the same orientation as the chondrocytes in the tissue. Although no similar structures have been found in the cartilage of any other species investigated, they have been found in cartilage repair tissue formed within a mechanically stimulated equine chondrocyte construct. Crystals were mainly located in superficial regions of cartilage, especially in joint regions of well-developed superficial layers, more often in yearlings than in adult horses. These results indicate that intramitochondrial crystals are related to the high mechanical stress in the horse joint and potentially also to the increased metabolic activity of immature individuals.(VLID)353386
Atomic Scale Self Accommodation Observed at hcp/dhcp Martensitic Transformation Interfaces
The martensitic hcp→dhcp transformation was studied in single crystals of Co-0.85at.%Fe by transmission electron microscopy (TEM) methods. During in-situ heating dhcp lamellae emerge into the hcp areas of the TEM specimens. The minimum thickness of the lamellae is about 15 close packed planes. Frequently lamellae are observed that grow in thickness by the movement of superledges that are up to about 100 close packed planes in height. The partials at the fronts of the transformation were analysed on an atomic level in TEM images with atomic resolution. The analysis shows that the transformation fronts consists of a sequence of very narrow dipoles compensating their long range strain fields. Since dipoles of a common Burgers vector are observed it is proposed that their short range interactions might promote their correlated nucleation
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