ATOM-PROBE MICROANALYSIS OF A NICKEL-BASE SINGLE-CRYSTAL SUPERALLOY

The atomic structure of a high strength single crystal nickel-base superalloy TMS-63 (Ni-7.8at%Cr-4.6at%Mo-12.8at%Al-2.8at%Ta) has been analysed using a field ion microscope/atom-probe equipped with a reflectron time-of-flight mass spectrometer. The equilibrium partitioning coefficient defined as the ratio of the solute concentration in the gamma' phase to that in the gamma phase has been found to be 0.22, 0.27, 2.3 and 3.3 for Cr, Mo, Al and Ta, respectively, in good agreement with our theoretical estimates. Ladder diagrams generated by progressively stripping the {200} planes of the gamma' revealed detailed information about the position of solute atoms in the crystal structure. These data were found to compare well against estimates made using cluster variation calculations.