title: The influence of tungsten on the chemical composition of a temporally evolving nanostructure of a model Ni-Al-Cr superalloy.
abstract: The influence of W on the temporal evolution of gamma' precipitation toward equilibrium in a model Ni-Al-Cr alloy is investigated by three-dimensional atom-probe (3DAP) microscopy and transmission electron microscopy (TEM). We report on the alloys Ni-10 Al-8.5 Cr (at.%) and Ni-10 Al-8.5 Cr-2 W (at.%), which were aged isothermally in the gamma + gamma' two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped gamma' precipitates, 5-15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (approximately 1023 m-3). As gamma' precipitates grow with aging at 1073 K, a transition from spheroidal- to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the gamma' precipitates are obtained as a function of aging time from three-dimensional atom-by-atom reconstructions. Proximity histogram concentration profiles (Hellman et al., 2000) of the quaternary alloy demonstrate that W concentration gradients exist in gamma' precipitates in the as-quenched and 0.25-h aging states, which disappear after 1 h of aging. The diffusion coefficient of W in gamma' is estimated to be 6.2 x 10-20 m2 s-1 at 1073 K. The W addition decreases the coarsening rate constant, and leads to stronger partitioning of Al to gamma' and Cr to gamma.
authors.affiliation: Department of Materials Science & Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208-3108, USA.
authors.forename: Chantal K
authors.initials: CK
authors.lastname: Sudbrack
authors.forename: Dieter
authors.initials: D
authors.lastname: Isheim
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Noebe
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Jacobson
authors.forename: David N
authors.initials: DN
authors.lastname: Seidman
mesh_terms: D000497:Alloys / Q000737:chemistry; D000535:Aluminum / Q000737:chemistry*; D011232:Chemical Precipitation; D002857:Chromium / Q000737:chemistry*; D004577:Electron Probe Microanalysis / Q000379:methods; D008854:Microscopy, Electron; D036103:Nanotechnology; D009532:Nickel / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry
chemical_list: D000497:Alloys; D002857:Chromium; D009532:Nickel; D000535:Aluminum; D014414:Tungsten