1. Nanoscale visualization of early  /  '-phase separation NSF Grant MET DMR-0241928, Northwestern University, David N. Seidman, PI Aging experiments at 600°C in a model Ni-7.5 Al-8.5 Cr at.% superalloy g = [111] 100 nm 10 nm Atom-probe tomography (APT), left, and transmission electron microscopy (TEM) images, above, allow for nanoscale visualization of  /  ’ phase separation. [110] APT image of a spheroidal Ni 3 Al x Cr (1-x)  ’- precipitate of radius ca. 9 nm. The (110) planes are clearly defined by Al (red) and Cr atoms (blue).

2. A high  '-precipitate number density (~10 24 precipitates m -3) is detected after 4 hours of aging at 600°C with atom-probe tomography (APT) The resulting composition profiles provide further insight into the phase separation behavior. Early  /  '-phase separation: sub-nanometer scale analyses NSF Grant MET DMR-0241928, Northwestern University, David N. Seidman, PI Precipitation in a model Ni-6.5 Al-9.5 Cr at.% superalloy aged at 600°C Corresponding composition profiles APT image

3. Nanostructural temporal evolution in  /  '-phase separation NSF Grant MET DMR-0241928, Northwestern University, David N. Seidman, PI Precipitation in a Ni-8.5 Al-10 Cr-1.0 Ru-1.0 Re at.% model superalloy Atom-probe tomograph (APT) images of a Ni-8.5 Al-10 Cr-1.0 Ru-1.0 Re at.% model superalloy aged at 600ºC for 15 minutes, acquired on the 3-D LEAP™ tomograph at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The morphologies of the  ’-precipitates are found to be a mixture of spheroidal and interconnected precipitates. - Courtesy of Ms. Gillian Hsieh, an R.E.U. student working with the group.

4. The Kinetic Pathway for Coarsening in a Ni-Al-Cr alloy by Lattice Kinetic Monte Carlo Simulation NSF Grant MET DMR-0241928, David N. Seidman, PI Long-range solute-vacancy binding LKMC 2 [110] [100] [110] [100] [110] [100] [110] [100] The kinetic pathway of coarsening in a Ni-5.24at.%Al-14.24 at.%Cr alloy is strongly dependent on long-range solute-vacancy binding energies. No long-range solute-vacancy binding LKMC 1 Concentration profiles as a function of distance from the  /  ’ interface, right-side. Experimental 3-D APT reconstructions follow LKMC 1 trajectories, which has long-range vacancy-solute binding energies out to fourth nearest neighbor. LKMC 1 - coagulation-coalescence LKMC 2 - classic evaporation-condensation

5. Effects of Ru, Re, or W on Model Ni-base Superalloys (2) NSF Grant MET DMR-0241928, Northwestern University, David N. Seidman, PI Dependence of Compositional Evolution at 800°C on Ru, Ru-Re, or Ru-Re-W additions 100 nm 10 nm [110] Ni-Cr-Al-Ru-Re-WNi-Cr-Al-Ru-ReNi-Cr-Al-Ru Compositional evolution of  ’-precipitates in Ni-8.5Cr-10Al-2Ru, Ni-8.5C5-10Al-1Ru-1Re and Ni- 8.5C5-10Al-.5Ru-.5Re-1W (at.%) during aging at 800 o C for up to 256 hours. Partitioning ratio, K, of an element is given by precipitate’s concentration of an element divided by matrix concentration the same element. Compositions measured by atom-probe analysis are all in atomic percent.

6. Effects of Ru, Re, or W on Model Ni-base Superalloys (1) NSF Grant MET DMR-0241928, Northwestern University, David N. Seidman, PI Dependence of Precipitate Size Evolution at 800°C on Ru, Ru-Re, and Ru-Re-W additions g = [111] 100 nm 10 nm Centered dark-field transmission electron microscopy (TEM) images of  ’-precipitates in Ni-8.5Cr- 10Al-2Ru, Ni-8.5C5-10Al-1Ru-1Re and Ni-8.5C5-10Al-.5Ru-.5Re-1W (at.%) after aging at 800 o C for 4, 16, 64, or 256 hours (left-side), and comparison of stereologically corrected 3-D precipitate- size distributions (PSDs) with the predictions of the Akaiwa-Voorhees model 1 for precipitated volume fractions of 20% (Ru-alloy) or 30% (Ru-Re and Ru-Re-W alloy) [110] 4 h16 h64 h256 h 100nm Ru Ru Re Ru Re W 4 h16 h64 h256 h 1 Akaiwa, N. and Voorhees, P.W., Phys. Rev. E 49 (1994) 3860.