Growth kinetics of antiphase domain in Ti₃Al intermetallic compound

Abstract

Growth kinetics of antiphase domain (APD) which increases the yield strength of Ti 3 Al by a factor of five, was investigated in Ti 3 Al compounds with compositions of 22.6, 24.6 and 34.7 at.%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-25 at.%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 ðSÞ 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. q

Effects of solute and vacancy segregation on antiphase boundary migration in stoichiometric and Al-rich Fe3Al: A phase-field simulation study

“…However, such an approach is problematic when the kinetics of micro-structural evolution is dominated by factors which we do not recognize. For instance, we detected segregation of solute atoms on APBs in Ti 3 Al [13]. Such segregation may cause solute-drag and affect apparent mobility of APDBs.…”

Phase-Field Simulation of Antiphase Boundary Migration in Intermetallic Compounds with Solute and Vacancy Segregation

“…A key factor for the stability of thermal APDs is segregation to APBs. For instance, we detected segregation of solute atoms at APBs in Ti 3 Al [5]. Such segregation may cause solute-drag and affect the apparent mobility of APBs.…”

“…Kinetic parameters needed for determining the rate of c Al -field evolution involved in the C-H equation was derived from the diffusivity data [14]. While the kinetic parameters for η-field evolution in Fe 3 Al was determined from the orderorder relaxation experimental data [15], but those for Ti 3 Al were determined from the APD growth experiment [5] since no order-order relaxation data was available. The c v -field was evolved so that the diffusion potential for vacancy was uniform throughout the simulation box assuming that the mobility of vacancies was extremely larger than those of constituting atoms.…”

Phase-Field Simulation of Antiphase Boundary Migration in Slightly Off-stoichiometric Fe₃Al with Solute and Vacancy Segregation

“…However, such an approach is problematic when the kinetics of microstructural evolution is affected by segregation. For instance, segregation of solute atoms on APBs [13] may cause solute-drag and decrease the apparent mobility of APDBs. Furthermore, it was observed that voids were formed along thermal APBs in CuZn [14].…”