Nickel-base superalloys are widely used for high temperature structural materials such as hot sections of jet turbine engines because they possess the ability to retain excellent creep and yield strengths at high temperatures (700 o C). These strengths are derived from the distribution in the microstructure of the main constituent phases: (Ni-FCC) and (L12-ordered structure based on Cu3Au). More specifically, a bi-modal distribution of provides the best combination of mechanical properties for commercial turbine disk alloys such as Rene 88 DT, and Rene 104 the alloy in this investigation [1]. The importance of this type of microstructure was demonstrated [2] for a similar alloy, showing that just subtle changes in the smaller (tertiary) distribution, resulting from different heat treatments, can profoundly improve the creep strength of disk alloys by inducing a remarkably sluggish creep deformation mechanism known as microtwinning [3]. This paper presents an examination of the effects of cooling rate on this and other microstructural parameters such as / interface widths, element partitioning phase composition, crystal ordering and precipitate size that also greatly impact the superalloy’s creep strength using Atom Probe Tomography. The microstructures, of which a typical atom probe reconstruction is shown in Figure 1, from samples linearly cooled at different cooling rates were examined and compared. The / interfacial widths, phase composition and element partitioning were obtained from proximity histograms [4] determined using Apex software [5].