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Transmission electron microscopic studies of twin structure of uranium dicarbide
JOURNAL
MATERIALS
45 (1%??./73)i 63-66.
ELECTRON
~IICROS~OPIC
02 NTJfX,EAR
TRANSMISSION
URANIUM
0 ~O~T~~~~~~,A~D
STUDIES
PUBLZSBINC
OF
TVVIN
CO., AMSTERDAM
STRUCTURE
OF
DICARBIDE
Up to the present, some observation of uranium carbide with tra~lsmi~ion ele tron
giving a current density of about 200 mA/cms. In order to remove the oxidized film on the thin
microscope have been made, whose eompos tion was limited to h~erstoiehiometri~ monoca bide
film, the difference of surface tension between aeeton and water was applied. Observations
containing less than 6.1 wt O/c carbon1-5. In addition to the difficulty of thinning techn que, the thin films of uranium carbide mus~ be thinner than most metals because of its high atomic number. Furthermore it is very reac ; ive, causing thin films to oxidize rapidly, an its brittle nature makes handling of thin Ims difficult. This letter is a preliminary r port i about a study of twin structure in ma ium dicarbide (U&s&l with a. transmission ele ‘d” tron microscope operated at 1000 kV. The specimens IJC$.SS (8.58 wt % C) were prepared by arc-melting of high purity ura ium
were carried out in a BEG-1000 electron microscope operated at 1000 kV. Preliminary metallographic studies were done to obtain a general feature of transformed &U%Z phase. A typical microstruoture of asmelt specimen observed with an optical microscope indicates a single phase of the uranium dicarbide as shown in fig. 1. This photograph shows a feature of shear ma~~nsitic transformation which is composed of twinned domains. A large number of internal microtwins were dimly observed in the martensite domain. The microstruoture of the as-melt
metal and spectroscopic grade carbon, i sing nonconsumable tungsten electrodes. These 1specimens were annealed in a tantalum resis & nce furnace at 1600 “C in vacuum of ml,3 x IO- bar (1 x 10-S torr). The thin films having ; reas suitable for transmission electron micros, ~opy were prepared by the following proced’ res. A slice about I mm thick was cut 08 w’ h a diamond-impregnated saw and was grou ~ to 0.3 mm with silicon carbide paper. The ele tropolishing apparatus is similar to that fo the case of Eyre et a1.13) and ~hitton*). A slice / was prehminarily thinned by electrolytica polishing in a 1 :l o~hophosphoric acid [ and methanol mixture, and subsequently finished by jet polishing using the electrolyte. The applied voltage was 4~5
Fig.
1.
Optical
micrograph
which indicates 63
of
as-melt
specimen
a single phase of UC%.
specimen observed microscope graph, but
in the transmission
electron
is shown in fig. 2. In this photo-
dislocation
lamellae
of
Iines were clearly the
microtwins
observed were
not.
A typical transmission electron microscopic structure of the annealed specimen is shown in fig.
3. Many
about 250-1250
microtwins
having
L%were observed.
intervals
of
Such micro-
twins were frequently observed more clearly in the annealed specimen than in the as-melt specimen. The same orientated plane of these microtwins was confirmed to be alternately arrayed from the contrasts of the bend extinetion contours m fig. 3 and of the dsrk-heid image. Furthermore it is noted that! microtwins sf large size and small size were alternately arrayed, having the mean width ratio 3 : 1. It is to say t,hat in real space the twinned domains are simply mirrored against a {I&l) plane. Consequently the twin spots can be
Fig.
2.
Transmission electron mierogmph
of as-melt
specimen.
TRANSMISSION
Fig.
3.
Transmission
electron
ELECTRON
micrograph
MICROSCOPIC
of
65
STUDIES
the specimen annealed at 1600 “C for 19 h.
axis. This microtwin plane was observed to be parallel to the electron beam. The trace of
from ,&UCs phase to ol-UC2 phase. As microtwins might be related to the dislocation
the microtwin plane in the bright-field image (fig. 4a) was perpendicular to the [Ii21direction of the coinciding spot in a selected-area diffrac-
behavior, further studies are required to clarify this relation in detail.
tion pattern (fig. 4b). Thus these microtwins are symmetrical about the (112) twinning plane. The microtwin structure of uranium dicarbide is identified to be a twin system of the type {112)1,.,.t.. This twin system is also expected to be reasonable from the crystallographic consideration of the n-UC2 phase (b.c.t.), being in agreement with the X-ray experimental result 6) and the electron diffraction analysis of UC& precipitation in hyperstoichiometric UCs). Lamellae of the microtwins observed in the martensite domain might be produced in accommodating the inhomogeneous strain of the martensitic transformation
Acknowledgement The authors are much indebted to Dr. T. Taoka (Japan Electron Optics Laboratory Co., Ltd.) for his valuable discussion. References B. L. Eyre and M. J. Sole, Phil. Mag. 9 (1964) 545
3,
B. L. Eyre
and M. J. Sole, J. Nucl.
(1966) 314 B. L. Eyre
and A.
(1967)
F.
Bartlett,
Phil.
Mater.
18
Mag.
15
995
J. L. Whitton,
J. Nucl. Mater.
12 (1964)
15
:; J. E. Bainbridge and L. Thore, J. Nucl. Mater. 34 (1970)
202
6) E. M. Horl, J. Nucl. Mater. 12 (1964) 193
(a) Another example of transmission electron micrograph of the specimen nnncaled at ? 60:: -i’ i’C;r Fig. 4. 12 kL presenting a typical microtwin domain. Intersections of the microtwin as swn 3x1 the u,;gh: :?oivr: corn er are frequently observed. Some precipitaticns arc also observed, which are ;mponsible ‘.:: k xLxt~i SdWll,il tic skcki1 fied. (lo) The selected-area diffraction pattern ofmicrotwins indicating ( L I 0) crystal. plant. cc:,
of dliffraction
pattern of (b) and each spot is indexed.
Notice
the spot doubling
parslEe
to
( i ! 2) d~rcc:tii~r:..
MATERIALS
45 (1%??./73)i 63-66.
ELECTRON
~IICROS~OPIC
02 NTJfX,EAR
TRANSMISSION
URANIUM
0 ~O~T~~~~~~,A~D
STUDIES
PUBLZSBINC
OF
TVVIN
CO., AMSTERDAM
STRUCTURE
OF
DICARBIDE
Up to the present, some observation of uranium carbide with tra~lsmi~ion ele tron
giving a current density of about 200 mA/cms. In order to remove the oxidized film on the thin
microscope have been made, whose eompos tion was limited to h~erstoiehiometri~ monoca bide
film, the difference of surface tension between aeeton and water was applied. Observations
containing less than 6.1 wt O/c carbon1-5. In addition to the difficulty of thinning techn que, the thin films of uranium carbide mus~ be thinner than most metals because of its high atomic number. Furthermore it is very reac ; ive, causing thin films to oxidize rapidly, an its brittle nature makes handling of thin Ims difficult. This letter is a preliminary r port i about a study of twin structure in ma ium dicarbide (U&s&l with a. transmission ele ‘d” tron microscope operated at 1000 kV. The specimens IJC$.SS (8.58 wt % C) were prepared by arc-melting of high purity ura ium
were carried out in a BEG-1000 electron microscope operated at 1000 kV. Preliminary metallographic studies were done to obtain a general feature of transformed &U%Z phase. A typical microstruoture of asmelt specimen observed with an optical microscope indicates a single phase of the uranium dicarbide as shown in fig. 1. This photograph shows a feature of shear ma~~nsitic transformation which is composed of twinned domains. A large number of internal microtwins were dimly observed in the martensite domain. The microstruoture of the as-melt
metal and spectroscopic grade carbon, i sing nonconsumable tungsten electrodes. These 1specimens were annealed in a tantalum resis & nce furnace at 1600 “C in vacuum of ml,3 x IO- bar (1 x 10-S torr). The thin films having ; reas suitable for transmission electron micros, ~opy were prepared by the following proced’ res. A slice about I mm thick was cut 08 w’ h a diamond-impregnated saw and was grou ~ to 0.3 mm with silicon carbide paper. The ele tropolishing apparatus is similar to that fo the case of Eyre et a1.13) and ~hitton*). A slice / was prehminarily thinned by electrolytica polishing in a 1 :l o~hophosphoric acid [ and methanol mixture, and subsequently finished by jet polishing using the electrolyte. The applied voltage was 4~5
Fig.
1.
Optical
micrograph
which indicates 63
of
as-melt
specimen
a single phase of UC%.
specimen observed microscope graph, but
in the transmission
electron
is shown in fig. 2. In this photo-
dislocation
lamellae
of
Iines were clearly the
microtwins
observed were
not.
A typical transmission electron microscopic structure of the annealed specimen is shown in fig.
3. Many
about 250-1250
microtwins
having
L%were observed.
intervals
of
Such micro-
twins were frequently observed more clearly in the annealed specimen than in the as-melt specimen. The same orientated plane of these microtwins was confirmed to be alternately arrayed from the contrasts of the bend extinetion contours m fig. 3 and of the dsrk-heid image. Furthermore it is noted that! microtwins sf large size and small size were alternately arrayed, having the mean width ratio 3 : 1. It is to say t,hat in real space the twinned domains are simply mirrored against a {I&l) plane. Consequently the twin spots can be
Fig.
2.
Transmission electron mierogmph
of as-melt
specimen.
TRANSMISSION
Fig.
3.
Transmission
electron
ELECTRON
micrograph
MICROSCOPIC
of
65
STUDIES
the specimen annealed at 1600 “C for 19 h.
axis. This microtwin plane was observed to be parallel to the electron beam. The trace of
from ,&UCs phase to ol-UC2 phase. As microtwins might be related to the dislocation
the microtwin plane in the bright-field image (fig. 4a) was perpendicular to the [Ii21direction of the coinciding spot in a selected-area diffrac-
behavior, further studies are required to clarify this relation in detail.
tion pattern (fig. 4b). Thus these microtwins are symmetrical about the (112) twinning plane. The microtwin structure of uranium dicarbide is identified to be a twin system of the type {112)1,.,.t.. This twin system is also expected to be reasonable from the crystallographic consideration of the n-UC2 phase (b.c.t.), being in agreement with the X-ray experimental result 6) and the electron diffraction analysis of UC& precipitation in hyperstoichiometric UCs). Lamellae of the microtwins observed in the martensite domain might be produced in accommodating the inhomogeneous strain of the martensitic transformation
Acknowledgement The authors are much indebted to Dr. T. Taoka (Japan Electron Optics Laboratory Co., Ltd.) for his valuable discussion. References B. L. Eyre and M. J. Sole, Phil. Mag. 9 (1964) 545
3,
B. L. Eyre
and M. J. Sole, J. Nucl.
(1966) 314 B. L. Eyre
and A.
(1967)
F.
Bartlett,
Phil.
Mater.
18
Mag.
15
995
J. L. Whitton,
J. Nucl. Mater.
12 (1964)
15
:; J. E. Bainbridge and L. Thore, J. Nucl. Mater. 34 (1970)
202
6) E. M. Horl, J. Nucl. Mater. 12 (1964) 193
(a) Another example of transmission electron micrograph of the specimen nnncaled at ? 60:: -i’ i’C;r Fig. 4. 12 kL presenting a typical microtwin domain. Intersections of the microtwin as swn 3x1 the u,;gh: :?oivr: corn er are frequently observed. Some precipitaticns arc also observed, which are ;mponsible ‘.:: k xLxt~i SdWll,il tic skcki1 fied. (lo) The selected-area diffraction pattern ofmicrotwins indicating ( L I 0) crystal. plant. cc:,
of dliffraction
pattern of (b) and each spot is indexed.
Notice
the spot doubling
parslEe
to
( i ! 2) d~rcc:tii~r:..