Abstract
Abstract The phase transition and thermal stability of long-period superstructures were examined in Ti-58.0 at.% Al, Ti-60.0 at.% Al and Ti-62.5 at.% Al single crystals focusing on reflections based on sets of lattice planes parallel to {310)fcc. Some long-period superstructures appear accompanied by obscure coherent boundaries in the L10 matrix. It was found that the AL5Ti′3 structure distinguished from the Al5Ti′3 structure is composed of only a Ti′3Al-type unimolecular cluster with the shape of fat rhombus on the Ti(002) layers. As the annealing temperature and Al concentration rose, transition of the long-period superstructures proceeded from the Al5Ti′3 to h-Al2Ti (ZrGa2-type) through the imperfectly ordered Al5Ti′3 structure. Peculiar streaks of electron diffraction appeared during the transition between the AL5Ti′3 and h-Al2Ti structures, suggesting the coexistence of at least two types of microcluster with fat and lean rhombi shapes corresponding to fourfold and threefold more periodicity respectively than the a axis of the L10 matrix.
Published Version
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