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http://dx.doi.org/10.3740/MRSK.2008.18.1.051

Crystal Structure and Morphology of Nitride Precipitates in TiAl  

Han, Chang-Suk (Dept. of Defense Science & Technology, Hoseo University)
Koo, Kyung-Wan (Dept. of Defense Science & Technology, Hoseo University)
Publication Information
Korean Journal of Materials Research / v.18, no.1, 2008 , pp. 51-56 More about this Journal
Abstract
The crystal structures and morphologies of precipitates in $L1_0$-ordered TiAl intermetallics containing nitrogen were investigated by transmission electron microscopy (TEM). Under aging at an approximate temperature of 1073 K after quenching from 1423 K, TiAl hardens appreciably due to the nitride precipitation. TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$-TiAl matrix, appear in the matrix preferentially at the dislocations. Selected area electron diffraction (SAED) pattern analyses showed that the needle-shaped precipitate is perovskite-type $Ti_3AlN$ (P-phase). The orientation relationship between the P-phase and the $L1_0$-TiAl matrix was found to be $(001)_P//(001)_{TiAl}\;and\;[010]_P//[010]_{TiAl}$. By aging at higher temperatures or for longer periods at 1073 K, plate-like precipitates of $Ti_2AlN$ (H-phase) with a hexagonal structure formed on the {111} planes of the $L1_0$-TiAl matrix. The orientation relationship between the $Ti_2AlN$ and the $L1_0$-TiAl matrix is $(0001)_H//(111)_{TiAl}\;and\;_H//_{TiAl}$.
Keywords
intermetallic compound; TiAl; precipitation; perovskite;
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