Superlattice dislocations and magnetic transition in Fe-Al alloys with the B2-type ordered structure

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.

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Observation of faint contrast at planar faults in alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108842 ◽

1978 ◽

Vol 36 (1) ◽

pp. 340-341

Author(s):

K. Kuroda ◽

Y. Tomokiyo ◽

T. Kumano ◽

T. Eguchi

Keyword(s):

Reciprocal Lattice ◽

Beam Theory ◽

Al Alloys ◽

Small Displacement ◽

Electron Microscopic ◽

Lattice Vector ◽

Fringe Contrast ◽

Planar Fault ◽

Lattice Displacement ◽

The Many

The contrast in electron microscopic images of planar faults in a crystal is characterized by a phase factor , where is the reciprocal lattice vector of the operating reflection, and the lattice displacement due to the fault under consideration. Within the two-beam theory a planar fault with an integer value of is invisible, but a detectable contrast is expected when the many-beam dynamical effect is not negligibly small. A weak fringe contrast is also expected when differs slightly from an integer owing to an additional small displacement of the lattice across the fault. These faint contrasts are termed as many-beam contrasts in the former case, and as ε fringe contrasts in the latter. In the present work stacking faults in Cu-Al alloys and antiphase boundaries (APB) in CuZn, FeCo and Fe-Al alloys were observed under such conditions as mentioned above, and the results were compared with the image profiles of the faults calculated in the systematic ten-beam approximation.

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Microstructure of an extruded rapidly solidified Al-8Fe-2Mo alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144218 ◽

1986 ◽

Vol 44 ◽

pp. 548-549

Author(s):

W. T. Donlon ◽

J. E. Allison ◽

S. Shinozaki

Keyword(s):

Electron Microscopy ◽

Automotive Industry ◽

Fuel Economy ◽

High Strength ◽

Al Alloys ◽

Light Weight ◽

Thin Sections ◽

Strength And Durability ◽

Rapidly Solidified ◽

Whitney Aircraft

Light weight materials which possess high strength and durability are being utilized by the automotive industry to increase fuel economy. Rapidly solidified (RS) Al alloys are currently being extensively studied for this purpose. In this investigation the microstructure of an extruded Al-8Fe-2Mo alloy, produced by Pratt & Whitney Aircraft, Goverment Products Div. was examined in a JE0L 2000FX AEM. Both electropolished thin sections, and extraction replicas were examined to characterize this material. The consolidation procedure for producing this material included a 9:1 extrusion at 340°C followed by a 16:1 extrusion at 400°C, utilizing RS powders which have also been characterized utilizing electron microscopy.

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Characterisation of planar crystal defects in Y2Fe17Cx (0.6 ≤ x ≤ 1.6) magnetic material by High Resolution Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177003 ◽

1990 ◽

Vol 48 (4) ◽

pp. 774-775

Author(s):

W. Coene ◽

F. Hakkens ◽

T.H. Jacobs ◽

K.H.J. Buschow

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Permanent Magnets ◽

Annealing Treatment ◽

High Resolution Electron Microscopy ◽

Crystal Defects ◽

Ordered Structure ◽

X Ray ◽

Planar Crystal ◽

Resolution Electron

Intermetallic compounds of the type RE2Fe17Cx (RE= rare earth element) are promising candidates for permanent magnets. In case of Y2Fe17Cx, the Curie temperature increases from 325 K for x =0 to 550 K for x = 1.6 . X ray and electron diffraction reveal a carbon - induced structural transformation in Y2Fe17Cx from the hexagonal Th2Ni17 - type (x < 0.6 ) to the rhombohedral Th2Zn17 - type ( x ≥ 0.6). Planar crystal defects introduce local sheets of different magnetic anisotropy as compared with the ordered structure, and therefore may have an important impact on the coercivivity mechanism .High resolution electron microscopy ( HREM ) on a Philips CM30 / Super Twin has been used to characterize planar crystal defects in rhombohedral Y2Fe17Cx ( x ≥ 0.6 ). The basal plane stacking sequences are imaged in the [100] - orientation, showing an ABC or ACB sequence of Y - atoms and Fe2 - dumbbells, for both coaxial twin variants, respectively . Compounds resulting from a 3 - week annealing treatment at high temperature ( Ta = 1000 - 1100°C ) contain a high density of planar defects.

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