Anomalous phonon stiffening associated with the (1 1 1) antiphase boundary in L12 Ni3Al. (1st January 2015)

• Record Type: Journal Article
• Authors: Manga, Venkateswara Rao; Shang, Shun-Li; Wang, William Yi; Wang, Yi; Liang, Jiang; Crespi, Vincent H.; Liu, Zi-Kui
• Is Part Of: Acta materialia. Volume 82(2015)
• Page Start: 287
• Page End: 294
• Publication Date: 2015-01-01
• Subjects: Antiphase boundary -- Thermodynamics -- Phonon -- First-principles calculations -- Ni3Al; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2014.09.005
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Antiphase boundaries (APBs) play a crucial role in the anomalous yield behavior exhibited by Ni3 Al with L12 structure. We investigated the changes in the vibrational properties associated with the formation of (0 0 1) and (1 1 1) APBs in Ni3 Al by employing first-principles calculations. The phonon density of states of Ni3 Al with and without (0 0 1) and (1 1 1) APBs revealed an interesting result: the (0 0 1) APB softens the phonons in its vicinity, while the (1 1 1) stiffens them. We also calculated the finite-temperature (0 0 1) and (1 1 1) APB Gibbs free energies from the first-principles quasi-harmonic approximation. The vibrational entropy of formation is positive (e.g. 0.053 mJ K −1 m −2 at 300 K) for the (0 0 1) APB and is negative (e.g. −0.0157 mJ K −1 m −2 at 300 K) for the (1 1 1) APB over the entire temperature range. We also find a significant change in the thermal electronic free energy due to the creation of the (0 0 1) or (1 1 1) APB. The anisotropy ratio of the APB energies, i.e. the ratio of the (1 1 1) APB free energy to the (0 0 1) APB free energy, changes from 2.9 at 300 K to 15.9 at 1000 K.