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ANALYTICAL ELECTRON MICROSCOPY OF RAPIDLY SOLIDIFIED METALS
T. F. Kelly, L. M. Holzman, Keesam Shin, Y.-W. Kim, J. C. Bae,
J. E. Flinn, P. P. Camus, and A. J. Melmed
Analytical electron microscopy has been an im-
portant part of studies of rapidly solidified
metals since the beginning of these studies.
This is largely due to the small dimensions of
characteristic microstructural features of rap-
idly solidified materials. Examples of the
need to characterize these materials on the
submicron scale are given below for two types
of rapidly solidified material: centrifugally
atomized steel powder and electrohydrodynami-
cally atomized submicron spheres.
Rapid solidification has a marked effect on
the precipitates in a material. A high-purity
alloy of Fe-40 wt% Ni was prepared by RSP.'
There should be no precipitates in the alloy
after heat treatment at 1200 C. This fact was
confirmed in a conventionally processed sister
material. However, the rapidly solidified ma-
terial has a large number density of small pre-
cipitates present. Figure 1(a) is a bright-
field image of an extraction replica taken from
the alloy. In addition to' some (Fe,Cr)23C6
carbides, aluminum oxide particles are found.
The x-ray spectrum in Fig. 1(b) is taken from
an aluminum oxide precipitat. These oxide
precipitates are not distinguishable from the
carbides by their appearance in the structure.
X-ray and EELS mapping of the elements in the
respective precipitates has been pursued in or-
der to learn about the relative number and dis-
tribution of the precipitate types.
A 304 SS that has been rapidly solidified by
centrifugal atomization2 was found to contain
a large number density of 1-2nm-diameter cavi-
ties. These cavities have been imaged by
through-focal bright-field and annular dark-
field imaging in a field-emission STEM (VG
HB501).3P The images are combined in an image
processor in order to demonstrate that the two
image types indicate the same features. This
approach eliminates the possibility of certain
artifacts (Fig. 2a). The thickness of the sam-
ple was measured by low-loss EELS5 to determine
the number density to be about 1023 m-3. We
conjecture that these cavities are stabilized
by an oxide coating, but they are too small to
analyze with confidence with AEM. This materi-
al was studied in an energy-compensated atom
probe and when oxygen was observed, it was
T. F. Kelly and L. M. Holzman are at the Ma-
terial Sciences Program; K. Shin, Y.-W. Kim,
and J. C. Bae are at the Department of Materi-
als Science and Engineering; and P. P. Camus
and A. J. Melmed are at the Applied Supercon-
ductivity Center, all at the University of Wis-
consin, Madison, WI 53706. J. E. Flinn is at
the Idaho National Engineering Laboratory,
EG&G, Idaho Falls, ID 83415.
present in a highly localized region (Fig. 2b).
These findings are consistent with our concepts
of oxide-stabilized cavities.
Pure elements and alloys have been processed
by electrohydrodynamic atomization to produce
droplets in the size range of 1 nm to 1 um in
diameter. The droplets cool at greater than
106 K/s and as a result, amorphous phases are
produced even in pure metals. Since pure amor-
phous metals solidified from the liquid had
never before been observed the atomic struc-
ture is of great interest. We have obtained
electron diffraction patterns by microdiffrac-
tion in a field emission STEM (VG HB501). The
particle shown in Fig. 3 has crystallized only
partially, an observation that provides infor-
mation about the temperature of nucleation and
the crystal growth rate. A radial distribution
function was determined for a pure amorphous
vanadium particle7 (Fig. 4) by recording of an
energy-filtered profile of the scattered inten-
sity as a function of scattering angle. These
data were converted into the radial distribu-
tion function by standard techniques.
1. K. Shin, M. S. Thesis, Dept. Mat. Sci.
Eng., U. Wisconsin, 1991.
2. R. N. Wright et al., MetaZZ. Trans. 19A:
3. D. F. Dawson-Elli et al., Materials Re-
search Society (R. M. Anderson, Ed.) 199: 75-
4. T. F. Kelly et al., Phil. Mag. (submit-
S. R. F. Egerton et al., Proc. 45th Ann.
Meeting EMSA, 1987, 123-124.
6. Y. W. Kim et al., Acta Metall. 37: 247-
7. L. M. Holzman et al., Proc. XII Int.
Cong. Elec. Micros., vol. 4.
8. This work has been supported by the Na-
tional Science Foundation, Grant DMR 8451933;
and the Department of Energy under Grant
DE-FG02-85ER45215 and Contract C87-101251.
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Kelly, T. F.; Holzman, L. M.; Shin, K.; Kim, Y. W.; Bae, J. C.; Flinn, J. E. et al. Analytical electron microscopy of rapidly solidified metals, article, December 1991; Madison, Wisconsin. (https://digital.library.unt.edu/ark:/67531/metadc619599/m1/1/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.