Long-range order relaxation and phase transformation in {gamma}-TiAl alloys
- CECM-CNRS, Vitry-Sur-Seine (France)
Residual electrical resistivity measurements were used for characterizing {gamma}-TiAl intermetallic compounds and for investigating the kinetics of long-range order (LRO) relaxation. In annealed and slowly cooled materials, a linear relationship between residual resistivity and aluminum content was observed in the composition range from 50 to 56.1 at.% Al. The isothermal relaxation of LRO after small temperature changes was investigated in {gamma}-TiAl compounds (with 49.8, 50.7, 52.6 and 54.1 at.% Al). The approach to equilibrium could be satisfactorily represented by a sum of two exponential relaxation processes. The slower process was assigned to LRO relaxation. From the investigation of the temperature dependence of relaxation times, an activation enthalpy of 2.97 {+-} 0.15 eV was determined for the stoichiometric alloy. This value is close to the activation enthalpy for titanium self-diffusion in TiAl. For Al contents higher than 50.7 at.%, the LRO changes were found to be superimposed on a supplementary phenomenon, which produces a continuous resistivity decrease. A TEM investigation showed that this drift was associated with the precipitation of Ti{sub 3}Al{sub 5}, which is a superstructure of the L1{sub 0} structure.
- OSTI ID:
- 357926
- Journal Information:
- Acta Materialia, Vol. 47, Issue 7; Other Information: PBD: 28 May 1999
- Country of Publication:
- United States
- Language:
- English
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