K. Muraleedharan et al., THE ALPHA(2)-TO-O TRANSFORMATION IN TI-AL-NB ALLOYS, Philosophical magazine. A. Physics of condensed matter. Defects and mechanical properties, 71(5), 1995, pp. 1011-1036
The alpha(2)-to-O transformation, with its characteristic microstructu
ral features, occurs across the entire range of compositions in alloys
based on the Ti3Al-Ti2AlNb system. In this paper, we describe the iso
thermal decomposition of the alpha(2)- to the O(O1)-phase in a Ti-28.5
at.% Al-13 at.% Nb alloy, in the first detailed study of this transfo
rmation. Both parent and product phases are ordered with an identical
site occupancy. The transformation is accomplished by a lattice distor
tion and a small composition change. The microstructural features and
patterns that evolve during the diffusional growth and coarsening of t
he O-phase are shown to be dominated by the strain energy associated w
ith the transformation. The orientation relationships, habit plane and
the self-accommodating nature of the product variants are therefore e
xplained by simple analyses in terms of the phenomenological theory of
martensitic transformations.