Phase-partitioning and site-substitution patterns of molybdenum in a model Ni-Al-Mo superalloy David N. Seidman, Northwestern University, DMR Atom-probe tomography (APT) and first-principles calculations are employed to investigate the partitioning and site-preference of Mo in the  (f.c.c.)-and  '(L1 2 )-phases in a model Ni-6.5Al-9.9Mo at.% superalloy. Mo partitions preferentially to the  (f.c.c.) matrix, with a driving force of 0.211eV from first-principles calculations. Al and Mo-centered partial radial distribution functions indicate that Mo occupies the Al sublattice sites of the Ni3Al(L1 2 ) phase. The average atomic displacements and forces are found to be smaller for Mo at the Al sublattice sites.

Kinetic Pathways for Phase Separation in a Ni-Al-Mo Alloy David N. Seidman, Northwestern University, DMR We investigated in detail the morphological, nanostructural and phase composition evolution of a model Ni–6.5Al–9.9Mo at.% superalloy during isothermal precipitation at 978 K for aging times ranging from 1/6 to 1024h. Temporal evolution of the  ’-phase nanostructure in Ni-6.5 Al-9.9Mo at.% alloys. The  /  ’ interfaces are delineated in red with Al iso-concentration surfaces. Two-phase separation regimes are identified: (1) concurrent coagulation and coalescence from 10 min to 16 h; (2) quasi-stationary state coarsening  ’-phase from 16 to 1024 h.

The order-disorder transition states of coherent interfaces in a ternary Ni-Al-Cr alloy David N. Seidman, Northwestern University, DMR The order-disorder transition across  (f.c.c.)/  ’(L1 2 ) coherent interfaces in a Ni-5.2Al-14.2 at.% alloy, are studied by a combined approach employing 3-D atom-probe tomography (APT) and lattice kinetic Monte- Carlo (LKMC) simulations. The snapshots of two close growing precipitates with antiphase chemical atomic arrangements at different aging times. There is a degree of LRO, S = 0.46, existing in the neck region. The temporal evolution of the concentration profiles of the fast diffusing elements, Ni and Al, across  (f.c.c.)/  ’(L12) interfaces determined via APT demonstrates the same strong transition trends, from an interfacial thickness of 1.7 nm (early growth stage) to 1.1 nm (later coarsening stage).

The Effects of temperature and ferromagnetism on the  - Ni/  ’-Ni 3 Al interfacial free energy David N. Seidman, Northwestern University, DMR The temperature dependencies of the  (f.c.c.)-Ni/  ’-Ni 3 Al(L1 2 ) interfacial free energies for the {100}, {110}, and {111} interfaces are calculated using first-principles calculations, including both coherency strain-energy and phonon vibrational entropy. The [100] direction is the elastically softest direction with the smallest coherency strains. The interfacial free energy of the (100) interface is smallest, which was determined using spin-polarized calculations. Wulff construction determined equilibrium  ’-Ni 3 Al (L1 2 ) morphology at 823 K based on first-principles calculated values of the (100), (110) and (111) interfacial free energies.

Temporal evolution of Ni-Al binary alloys David N. Seidman, Northwestern University, DMR Precipitation strengthening in these alloys is achieved through the nucleation, growth, and coarsening of an ordered Ni 3 Al phase (γ’(L1 2 )- precipitate phase) from the disordered Ni-rich matrix (γ(f.c.c.)-phase) due to phase separation. Morphological evolution of the γ’(L12)-precipitates in a binary Ni-Al alloy from specimens aged for: (a) 1/4; (b) 1; (c) 16; (d) 1024, and (e) 4096 h. The alignment of the γ’(L1 2 )- precipitates along a -type direction is indicated for 4096 h. 3D atom-probe tomographic reconstruction of a binary Ni-Al alloy aged at 873 K for 1 h. The specimen was examined using 5 pJ, 200 KHz pulse repetition rate, 35 K, and a 5% detection rate. Nickel atoms are in green and Al atoms are red.

Educational Outreach and Broader Impacts David N. Seidman, Northwestern University, DMR Elizaveta Plotnikov (PhD candidate) teaching 8 th graders about phase diagrams at an outreach event. Presentations about science given to middle and high school students at NU included: NU Career Day for Girls NU Splash 2012 Take Our Sons and Daughters to Work Day High school students learn about refractive indicies of liquids at an educational outreach event on the Northwestern campus organized by Elizaveta Plotnikov (Ph.D. candidate) – nusplash.learningu.org