Growth morphology and crystallography of precipitate in a new high-temperature structural intermetallic Ti–40Al–10Fe

Abstract

Based on TiAl alloys bearing high levels of Nb, which are prospective high-temperature intermetallics, a new dual-phase alloy (Ti–40Al–10Fe (at%)) with precipitate growth direction close to the slipping plane normal of the matrix was developed. Transmission electron microscopy revealed that the annealed alloy was composed of equiaxed grains of τ2-TiAl2Fe and γ-TiAl phases. Aging treatment at 1000 °C produced polygon-shaped γ-TiAl precipitate from the τ2-TiAl2Fe matrix. The precipitation reaction of the face-centered cubic structure of τ2-TiAl2Fe into the ordered face-centered tetragonal structure of γ-TiAl phase was systematically investigated in terms of crystallographic features, including mutual orientation relationship, growth direction, habit plane, side facets, and interfacial dislocation structure. The observed growth direction <973> was close to the normal of the slip plane {111}, with a discrepancy angle of ∼20°. Thus, the observed two-phase microstructure might significantly improve strengthening. It could also be quantitatively controlled by selection of precipitate and matrix with phase structures and lattice parameters that meet a certain requirement.