Phase-transformation mechanisms in two-phase TiAl-based alloys
- Univ. of Birmingham (United Kingdom). IRC in Materials for High Performance Applications
- Office National d`Etudes et de Recherches Aerospatiales, Chatillon (France)
The complexity of the phase diagram for the chemical composition range of two-phase TiAl-based alloys results in the occurrence of numerous phase transformation modes, such as formation of a two-phase {gamma}/{alpha}{sub 2} lamellar structure, discontinuous coarsening of the lamellar structure and massive a to {gamma} transformation. The purpose of the present work is to determine the mechanisms involved in these transformations by paying particular attention to the ordered character of the {gamma} phase. The mechanisms that the authors propose are as follows: (1) the lamellar structure formation is strongly related to the propagation of Shockley partial dislocations. The formation of {gamma} lamellae is achieved by nucleation, growth and encountering of numerous ordered domains on a given stacking fault of the hexagonal structure, (2) the occurrence of the discontinuous coarsening phenomenon is explained by the presence of highly stable interfaces in the primary lamellar structure, which renders the normal coarsening (thickening) difficult, (3) the formation of the lamellar {gamma} phase is replaced during rapid cooling by the massive formation of the {gamma} phase and its nucleation occurs on grain boundaries by the formation of a nucleus coherent with one of the two grains. The growth of this massive {gamma} phase takes place into the opposite grain through thermally activated jumps of individual atoms across an incoherent {alpha}/{gamma} interface. In the present paper, these transformation mechanisms will be described in detail and discussed.
- OSTI ID:
- 225084
- Report Number(s):
- CONF-950201--; ISBN 0-87339-304-X
- Country of Publication:
- United States
- Language:
- English
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