TY - JOUR
T1 - Long-period ordering in a TiAl single crystal with a gradient composition
AU - Hata, S.
AU - Shiraishi, K.
AU - Itakura, M.
AU - Kuwano, N.
AU - Nakano, T.
AU - Umakoshi, Y.
N1 - Funding Information:
The authors thank Dr R. Kainuma (Tohoku University) and Dr T. Ikeda (Osaka University) for their valuable comments on preparing TiAl single crystals with gradient compositions. This work was partly supported by a Grant-in-Aid for Young Scientists (B) (15710092) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Priority Assistance of the Formation of Worldwide Renowned Centers of Research—The 21st Century COE Program (Project: Center of Excellence for Advanced Structural and Functional Materials Design) from the MEXT. This work was also partly carried out at the Strategic Research Base ‘Handai Frontier Research Center’ supported by the Japanese Government’s Special Coordination Fund for Promoting Science and Technology.
PY - 2005/4
Y1 - 2005/4
N2 - A series of long-period superstructures (LPSs) formed in an Al-rich TiAl single crystal with a gradient composition has been observed by transmission electron microscopy. A Ti-54.7?at.%?Al single crystal was heat treated within molten Al at 1234°C, and a composition-gradient layer with an Al concentration from 55 to 75?at.% was formed at the surface of the single crystal. The composition-gradient layer exhibits ordering into different LPSs depending on the Al concentration as follows: short-range order, h-Al2Ti and one-dimensional antiphase domain structure. These LPSs have an alternate stacking of Al(002) and Ti-Al(002) layers and the ordering of the LPSs proceeds in the TiAl matrix, maintaining an orientation relationship in which Al(002) layers of the LPSs and the TiAl matrix are parallel to each other. The ordering of this type of LPS and the phase transition between these LPSs are thus interpreted as structural changes in Ti(002) layers of the Al-rich TiAl crystal. It was also observed that ordering of the orthorhombic h-Al2Ti exhibits anisotropic features depending on the direction of the composition gradient. This suggests that the long-period ordering in the TiAl crystal depends on diffusion processes as well as the local concentrations of Ti and Al atoms.
AB - A series of long-period superstructures (LPSs) formed in an Al-rich TiAl single crystal with a gradient composition has been observed by transmission electron microscopy. A Ti-54.7?at.%?Al single crystal was heat treated within molten Al at 1234°C, and a composition-gradient layer with an Al concentration from 55 to 75?at.% was formed at the surface of the single crystal. The composition-gradient layer exhibits ordering into different LPSs depending on the Al concentration as follows: short-range order, h-Al2Ti and one-dimensional antiphase domain structure. These LPSs have an alternate stacking of Al(002) and Ti-Al(002) layers and the ordering of the LPSs proceeds in the TiAl matrix, maintaining an orientation relationship in which Al(002) layers of the LPSs and the TiAl matrix are parallel to each other. The ordering of this type of LPS and the phase transition between these LPSs are thus interpreted as structural changes in Ti(002) layers of the Al-rich TiAl crystal. It was also observed that ordering of the orthorhombic h-Al2Ti exhibits anisotropic features depending on the direction of the composition gradient. This suggests that the long-period ordering in the TiAl crystal depends on diffusion processes as well as the local concentrations of Ti and Al atoms.
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U2 - 10.1080/09500830500157462
DO - 10.1080/09500830500157462
M3 - Article
AN - SCOPUS:32144458962
SN - 0950-0839
VL - 85
SP - 175
EP - 185
JO - Philosophical Magazine Letters
JF - Philosophical Magazine Letters
IS - 4
ER -