Growth kinetics of antiphase domain (APD) which increases the yield strength of Ti3Al by a factor of five, was investigated in Ti 3Al compounds with compositions of 22.6, 24.6 and 34.7at.%Al by quenching from disordered state and subsequent isothermal annealing at 973-1173 K. The variation in APD size exhibited positive deviation from the conventional 'parabolic-growth-law' in the early stage in all the compounds, while negative deviations were observed in the late stage in all the compounds except the stoichiometric one (Ti-25at.%Al). The variation in the APD size in the stoichiometric compound was numerically calculated by considering the variation in the long range order in the matrix (S) and that in the mobility of the APDBs which was enhanced by non-equilibrium excess vacancies which were introduced by the quenching. The calculated variations in APD size could be successfully fitted to the experimental results in the early stage, and therefore, the positive deviation was attributed to the enhancement of the mobility of APDBs by the excess vacancies. In the late stage, the segregation of excess atoms (i.e. Ti atoms in Ti-rich composition and Al atoms in Al-rich composition) was detected in the compounds of off-stoichiometric composition by energy-dispersive X-ray spectroscopy, while any heterogeneity of composition was not observed in the stoichiometric compound. Faceted APDBs were observed in this stage. The mechanism of the negative deviation was attributed to the segregation and the facet which decrease the mobility and/or the driving force of the APDB migration.
ASJC Scopus subject areas