Abstract
The atomic arrangements of short-range order (SRO) in two Al-rich Ī³-TiAl alloys with 62.5 and 60.0at.%Al respectively have been investigated by high-resolution transmission electron microscopy with image processing. For both alloys, SRO structures are formed in Ti-rich (002) layers of the L10 ordered Ī³-TiAl matrix, in the course of the phase transformation from the Al5 Ti3 long-period superstructure phase at lower temperatures to the h-Al2 Ti phase at higher temperatures. The SRO structures are composed of three types of ordered cluster: Ti4 Al type (square shaped), Ti3 Al type (fat rhombus shaped) and Ti2 Al type (lean rhombus shaped). The ordered clusters form local microdomains of the Al5 Ti3 and Al3 Ti2 superstructures in addition to the Al5 Ti3 and h-Al2 Ti superstructures, by different methods of tiling the ordered clusters. Such ordered clusters or microdomains tend to be in contact with each other through common {310) boundaries. This results in peculiar diffuse streaks in diffraction connecting intensity maxima arising from the long-period superstructures.
Published Version
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