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

• New dual-phase TiAL-based intermetallic alloy Ti–40Al–10Fe was developed on the basis of Ti–48Al–10Nb to reduce fabrication cost without losing strengthening.
• Two types of gamma-TiAl precipitates including round-shaped and polygon-shaped variants were observed to occur in TiAl(2)Fe matrix.
• A detailed investigation to the crystallographic features of gamma-TiAl precipitate in TiAl(2)Fe matrix, including orientation relationship, habit plane, side facets, growth direction and interfacial dislocation, were carried out with TEM method.
• Crystallographic features of the polygon-shaped gamma-TiAl precipitate were rationally interpreted by using invariant deformation element model for diffusional phase transformations.

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.

The gamma-TiAl precipitate in TiAl(2)Fe matrix, including orientation relationship, habit plane(6–56), side facet (115), growth direction [97-3] and interfacial dislocation, were carried out with TEM method.Figure optionsDownload as PowerPoint slide