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Electron irradiation damage in titanium carbide
111
Journal of the Less-Common Metals, 70 (1980) 111 - 113 @ Elsevier Sequoia S.A., Lausanne -Printed in the Netherlands
Letter
Electron irradiation damage in titanium carbide
D. K. CHATTERJEE* Systems (U.S.A.)
Research
Laboratories
Inc., 2800 Indian Ripple
Road,
Dayton,
Ohio 45440
H. A. LIPSITT Air Force Materials 45433 (U.S.A.) (Received
Laboratory
(AFML/LLM),
Wright-Patterson
Air Force Base, Ohio
July 18,1979)
The electron irradiation of compounds with widely differing atomic masses permits the selective displacement of one species by another through a careful choice of the incident electron energy. In this investigation evidence of damage produced in TiC by low energy electron irradiation was observed and is reported for the first time. TiC falls into a class of transition metal carbides which assume an NaCltype structure; the heavier titanium metal atoms assume the lattice positions and the lighter carbon atoms occupy the octahedral positions. This material possesses very high strength and melting point, and the Ti-C bond is thought to be predominantly covalent in nature. Deformed single crystals of TiC,,ss having the (001) orientation were electrolytically thinned for electron transparency, as described elsewhere [l] . The thin foils thus produced were examined using the heating stage of a Philips EM300 electron microscope operated at 100 kV. In the heating stage the specimens were heated at temperatures ranging from 700 to 950 “c in 50 “c increments. During examination of these foils, with the condenser lenses of the microscope removed, instantaneous void formation was observed in the localized area of the foil irradiated by the electron beam for temperatures of 800 “c and above. Figure 1 is a series of electron micrographs taken from a single foil showing (a) the area before irradiation, (b) the same area after irradiation at 800 Y! and (c) the area adjacent to the irradiated area (about 10 I.cmaway). Stereomicroscopy confirmed the threedimensional nature of the voids in the irradiated region. The area adjacent to the irradiated region did not reveal the presence of voids, confirming that the damage occurred only in the irradiated region.
*On leave from the Defense Metallurgical
Research Laboratory,
Hyderabad,
India.
(c) Fig. 1. (a) Area of a thin foil before irradiation; (b) the same area as in (a) after electron irradiation at 800 “c, showing voids; (c) an area adjacent to (b) which is unaffected by electron irradiation. Foil orientation (001).
Void formation in a refractory material such as TiC for such a low electron energy irradiation (i.e. 100 kV) is somewhat surprising; however, Venables and Lye [ 2 ] have shown that electron-radiation-induced disordering occurs in VC at 100 kV by the displacement of carbon atoms. The energy required to displace a carbon atom from the octahedral site of a Tic lattice is expected to be smaller than that required for a carbon atom in graphite.. In graphite, radiation damage has been observed [3] at electron energies as low as 120 kV. Hence the observation of voids produced in TiC presumably by the displacement of lighter carbon atoms at 100 kV is reasonable. Also, in this ~vestigation a substoichiomet~c Tic single crystal was used for electron irradiation. This crystal had vacant carbon lattice sites prior to irradiation, and the microstructure consisted of a high density of dislocations with tangles and vacancy loops. Since the formation of voids is intimately related [ 41 to the preexisting microstructure and also to the disposition of the inter-
113
stitial atoms, the deformed microstructure formation in TiC0,93.
is thought to influence the void
This work was supported in part under Air Force Contract F33615-7% C-5037. The assistance of Ms. M. Whitaker and Ms. H. Bailey in the preparation of the manuscript is gratefully acknowledged. 1 D. K. Chatterjee, M, 0. Mendiratta and H. A. Lipsitt, J. Muter. Sci., to be published. 2 J. D. Venables and R. G. Lye, Philos. Nag., 19 (159) (1969) 565. 3 S. M. Ohr, A. Wolfenden and T. S. Noggle, in G. Thomas (ea.), Electron Microscopy and Structure of Materials, University of California Press, Berkeley, California, 1972, p. 964. 4 A. Wolfenden, K. Farrell and J. 0. Stiegler, in G. Thomas fed.), Electron ~jcroscopy and Structure of Muteriak, University of California Press, Berkeley, California, 1972, p. 984.
Journal of the Less-Common Metals, 70 (1980) 111 - 113 @ Elsevier Sequoia S.A., Lausanne -Printed in the Netherlands
Letter
Electron irradiation damage in titanium carbide
D. K. CHATTERJEE* Systems (U.S.A.)
Research
Laboratories
Inc., 2800 Indian Ripple
Road,
Dayton,
Ohio 45440
H. A. LIPSITT Air Force Materials 45433 (U.S.A.) (Received
Laboratory
(AFML/LLM),
Wright-Patterson
Air Force Base, Ohio
July 18,1979)
The electron irradiation of compounds with widely differing atomic masses permits the selective displacement of one species by another through a careful choice of the incident electron energy. In this investigation evidence of damage produced in TiC by low energy electron irradiation was observed and is reported for the first time. TiC falls into a class of transition metal carbides which assume an NaCltype structure; the heavier titanium metal atoms assume the lattice positions and the lighter carbon atoms occupy the octahedral positions. This material possesses very high strength and melting point, and the Ti-C bond is thought to be predominantly covalent in nature. Deformed single crystals of TiC,,ss having the (001) orientation were electrolytically thinned for electron transparency, as described elsewhere [l] . The thin foils thus produced were examined using the heating stage of a Philips EM300 electron microscope operated at 100 kV. In the heating stage the specimens were heated at temperatures ranging from 700 to 950 “c in 50 “c increments. During examination of these foils, with the condenser lenses of the microscope removed, instantaneous void formation was observed in the localized area of the foil irradiated by the electron beam for temperatures of 800 “c and above. Figure 1 is a series of electron micrographs taken from a single foil showing (a) the area before irradiation, (b) the same area after irradiation at 800 Y! and (c) the area adjacent to the irradiated area (about 10 I.cmaway). Stereomicroscopy confirmed the threedimensional nature of the voids in the irradiated region. The area adjacent to the irradiated region did not reveal the presence of voids, confirming that the damage occurred only in the irradiated region.
*On leave from the Defense Metallurgical
Research Laboratory,
Hyderabad,
India.
(c) Fig. 1. (a) Area of a thin foil before irradiation; (b) the same area as in (a) after electron irradiation at 800 “c, showing voids; (c) an area adjacent to (b) which is unaffected by electron irradiation. Foil orientation (001).
Void formation in a refractory material such as TiC for such a low electron energy irradiation (i.e. 100 kV) is somewhat surprising; however, Venables and Lye [ 2 ] have shown that electron-radiation-induced disordering occurs in VC at 100 kV by the displacement of carbon atoms. The energy required to displace a carbon atom from the octahedral site of a Tic lattice is expected to be smaller than that required for a carbon atom in graphite.. In graphite, radiation damage has been observed [3] at electron energies as low as 120 kV. Hence the observation of voids produced in TiC presumably by the displacement of lighter carbon atoms at 100 kV is reasonable. Also, in this ~vestigation a substoichiomet~c Tic single crystal was used for electron irradiation. This crystal had vacant carbon lattice sites prior to irradiation, and the microstructure consisted of a high density of dislocations with tangles and vacancy loops. Since the formation of voids is intimately related [ 41 to the preexisting microstructure and also to the disposition of the inter-
113
stitial atoms, the deformed microstructure formation in TiC0,93.
is thought to influence the void
This work was supported in part under Air Force Contract F33615-7% C-5037. The assistance of Ms. M. Whitaker and Ms. H. Bailey in the preparation of the manuscript is gratefully acknowledged. 1 D. K. Chatterjee, M, 0. Mendiratta and H. A. Lipsitt, J. Muter. Sci., to be published. 2 J. D. Venables and R. G. Lye, Philos. Nag., 19 (159) (1969) 565. 3 S. M. Ohr, A. Wolfenden and T. S. Noggle, in G. Thomas (ea.), Electron Microscopy and Structure of Materials, University of California Press, Berkeley, California, 1972, p. 964. 4 A. Wolfenden, K. Farrell and J. 0. Stiegler, in G. Thomas fed.), Electron ~jcroscopy and Structure of Muteriak, University of California Press, Berkeley, California, 1972, p. 984.