Role of the antiphase-boundary energy in periodic-to-quasiperiodic superlattice transitions: A Monte Carlo simulation of ordering in Al-rich γ-TiAl

Abstract

Results of the strip projection method have established that formation of antiphase boundaries (APBs) is the initial stage of a periodic-to-quasiperiodic transformation in superlattices. The Al₅Ti₃−to-quasiperiodic superlattice transformation, observed in Al-rich γ-TiAl intermetallics, is a classic example of such a transition. Energy of the relevant APBs would, therefore, be expected to play an important role in the occurrence of this transition. In the two-dimensional Monte Carlo simulations carried out in this work, change in the APB energy, accomplished by suitably altering the pair interaction energies, was found to explain the diffraction effects observed in the alloys with various compositions depicting this transition. The results of the simulation bring out salient features of the atomic arrangements in imperfectly ordered quasiperiodic and near-quasiperiodic structures encountered in this transition.