Phase-partitioning and site-substitution patterns of molybdenum in a model Ni-Al-Mo superalloy: An atom-probe tomographic and first-principles study

Atom-probe tomography (APT) and first-principles calculations are employed to investigate the partitioning of Mo in the gamma(f.c.c.)-and gamma'(L1(2))-phases in a model Ni-6.5Al-9.9Mo at. % superalloy. Mo is experimentally observed to partition preferentially to the gamma(f.c.c.)-matrix, which is consistent with the smaller value of the gamma(f.c.c.)-matrix substitutional formation-energy, with a driving force of 0.707 eV for partitioning as determined by first-principles calculations. APT measurements of the gamma'(L12)-precipitate-phase composition and Al-, Mo-centered partial radial distribution functions indicate that Mo occupies the Al sublattice sites of the Ni3Al(L1(2)) phase. The preferential site-substitution of Mo at Al sublattice sites is confirmed by first-principles calculations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4753929]