Microscopic mechanisms of metastable phase formation during ball milling of intermetallic TiAl phases
- GKSS Research Centre, Geesthacht (Germany)
Powders of the intermetallic equilibrium phases {alpha}{sub 2}-Ti{sub 3}Al, {gamma}-TiAl and TiAl{sub 3} were ball milled in order to investigate the microscopic origins of the energetic destabilization and the transformation into metastable phases during the milling process. It was found that the intermetallic phases were chemically partially disordered on milling followed by the transformation into solid solution phases after long milling. In detail, for the {gamma} phase, the formation of numerous deformation twins, thin h.c.p. lamellae and lamellae of the 9R phase formed by an antitwin operation was observed by TEM. The disordering of the D0{sub 22}-TiAl{sub 3} phase occurred inhomogeneously in the material via the formation of antiphase boundaries on (001) planes, resulting in a f.c.c. solid solution in the final state. In summary, it can be concluded that the formation of the observed metastable phases results from chemical disordering, whereas the excess enthalpy of grain boundaries plays only a minor role for the energetical destabilization of the intermetallic compounds during milling in this case.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-91ER45439
- OSTI ID:
- 540969
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 9 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
Similar Records
Phase transformation mechanisms involved in two-phase TiAl-based alloys. 1: Discontinuous coarsening and massive-type transformation
Phase transformation mechanisms involved in two-phase TiAl-based alloys. 1: Lamellar structure formation