Structure of perovskite carbide and nitride precipitates in L10-ordered TiAl

Abstract

The crystallographic structures of carbide and nitride formed in TiAl containing carbon and nitrogen have been investigated using transmission electron microscopy. The needle-shaped carbide and nitride are formed parallel to only the [001] direction of the L1₀-ordered TiAl matrix. Detailed analyses in terms of selected area electron diffraction and dark-field electron microscopy revealed that the needle-shaped carbide and nitride have a crystal structure of perovskite type and have long-range carbon-vacancy and nitrogen-vacancy ordering below a critical temperature. The domain of the long-range order rotates periodically about the axis of the needle by 90[ddot] resulting in the repeated formation of antiphase boundaries along the needle. At higher temperatures, long-range ordering disappears indicating uniform distribution of carbon and nitrogen in the needle-shaped perovskite carbide and nitride.