Compositional Variations Between Different Generations of Gamma Precipitates Forming During Continuous Cooling of a Commercial Nickel-Base Superalloy
NORTH TEXAS STATE UNIV DENTON
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The compositional and microstructural evolution of different generations of precipitates of the ordered gamma phase during the continuous cooling, followed by isothermal aging, of a commercial nickel-base superalloy. Rene 88DT, has been characterized by three dimensional atom probe 3DAP tomography coupled with energy-filtered transmission electron microscopy EFTEM studies. After solutionizing in the single gamma-phase field, during continuous cooling at a relatively slow rate 24 deg CMin, the first generation primary gamma precipitates, forming at relatively higher temperatures, exhibit near-equilibrium compositions, while the smaller-scale secondary gamma precipitates, forming at lower temperatures, exhibit nonequilibrium compositions often containing an excess of Co and Cr while being depleted in Al and Ti content. The compositions of the gamma matrix near these precipitates also exhibit similar trends, with the composition being closer to equilibrium near the primary precipitates as compared to the secondary precipitates. Subsequent isothermal aging at 760 deg C leads to coarsening of the primary gamma precipitates without affecting their composition significantly. In contrast, the composition of the secondary gamma precipitates is driven toward equilibrium during the isothermal aging process.
- Physical Chemistry
- Metallurgy and Metallography
- Nuclear Physics and Elementary Particle Physics