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Type Sudbrack, Chantal K.; Isheim, Dieter; Noebe, Ronald D.; Jacobson, Nathan S.; Seidman, David N.
  Publication The Influence of Tungsten on the Chemical Composition of a Temporally Evolving Nanostructureof a Model Ni-Al-Cr Superalloy Volume Journal Article
Pages 2004
  Abstract Microscopy and Microanalysis  
  Corporate Author Microsc. Microanal.  
Publisher 10  
  Summary Language 355-365 Series Editor nickel-base superalloy; three-dimensional atom-probe microscopy; tungsten; aluminum; chromium; temporal evolution; decomposition; coarsening; nanostructure; partitioning ratio; proxigram  
Abbreviated Series Title The influence of W on the temporal evolution of ?' 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-prime two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped gamma-prime precipitates, 5-15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (~1023 m-3). As gamma-prime precipitates grow with aging at 1073 K, a transition from spheriodal to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the gamma-prime precipitates are obtained as a function of aging time from 3D atom-by-atom reconstructions. Proximity histogram concentration profiles (Hellman et al., 2000) of the quaternary alloy demonstrate that W concentration gradients exist in gamma-prime 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-prime 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-prime and Cr to gamma.
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yes NU @ c-sudbrack @ 200
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