Anomalous phonon stiffening associated with the (1 1 1) antiphase boundary in L12 Ni3Al

Venkateswara Rao Manga, Shun Li Shang, William Yi Wang, Yi Wang, Jiang Liang, Vincent H. Crespi, Zi Kui Liu

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Abstract

Antiphase boundaries (APBs) play a crucial role in the anomalous yield behavior exhibited by Ni3Al 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 Ni3Al by employing first-principles calculations. The phonon density of states of Ni3Al 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.

Original languageEnglish (US)
Pages (from-to)287-294
Number of pages8
JournalActa Materialia
Volume82
DOIs
StatePublished - Jan 1 2015

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All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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