TITLE

Effects of temperature and ferromagnetism on the γ-Ni/γ′-NiAl interfacial free energy from first principles calculations

AUTHOR(S)
Mao, Zugang; Booth-Morrison, Christopher; Plotnikov, Elizaveta; Seidman, David
PUB. DATE
November 2012
SOURCE
Journal of Materials Science;Nov2012, Vol. 47 Issue 21, p7653
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The temperature dependencies of the γ(f.c.c.)-Ni/γ′-NiAl(L1) interfacial free energy for the {100}, {110}, and {111} interfaces are calculated using first-principles calculations, including both coherency strain energy and phonon vibrational entropy. Calculations performed including ferromagnetic effects predict that the {100}-type interface has the smallest free energy at different elevated temperatures, while alternatively the {111}-type interface has the smallest free energy when ferromagnetism is absent; the latter result is inconsistent with experimental observations of γ′-NiAl-precipitates in Ni-Al alloys faceted strongly on {100}-type planes. The γ(f.c.c.)-Ni/γ′-NiAl interfacial free energies for the {100}, {110}, and {111} interfaces decrease with increasing temperature due to vibrational entropy. The predicted morphology of γ′-NiAl(L1) precipitates, based on a Wulff construction, is a Great Rhombicuboctahedron (or Truncated Cuboctahedron), which is one of the 13 Archimedean solids, with 6-{100}, 12-{110}, and 8-{111} facets. The first-principles calculated morphology of a γ′-NiAl(L1) precipitate is in agreement with experimental three-dimensional atom-probe tomographic observations of cuboidal L1 precipitates with large {100}-type facets in a Ni-13.0 at.% Al alloy aged at 823 K for 4096 h. At 823 K this alloy has a lattice parameter mismatch of 0.004 ± 0.001 between the γ(f.c.c.)-Ni-matrix and the γ′-NiAl-precipitates.
ACCESSION #
78437624

 

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