Abstract
The compositional and microstructural evolution of different generations of precipitates of the ordered γ′ 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 γ-phase field, during continuous cooling at a relatively slow rate (∼24 °C/min), the first-generation primary γ′ precipitates, forming at relatively higher temperatures, exhibit near-equilibrium compositions, while the smaller-scale secondary γ′ 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 γ 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 °C leads to coarsening of the primary γ′ precipitates without affecting their composition significantly. In contrast, the composition of the secondary γ′ precipitates is driven toward equilibrium during the isothermal aging process.
| Original language | English |
|---|---|
| Pages (from-to) | 3059-3068 |
| Number of pages | 10 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 40 |
| Issue number | 13 |
| DOIs | |
| State | Published - Dec 2009 |
| Externally published | Yes |
Funding
The bulk chemical composition of the commercially procured Rene 88DT alloy was 56.53Ni-16.24Cr-13.27Co-3.92Ti-2.09Al-4.08Mo-3.92W-0.76Nb (wt pct) or 55.63Ni-18.02Cr-13.00Co-4.74Ti-4.45Al-2.48Mo-1.21W-0.46Nb (at. pct). Material was cut from the bore and rim section of a disk, produced and tested under work supported by the United States Defense Advanced Research Projects Agency, Defense Sciences Office (Engine Systems Prognosis, Contract Nos. HR0011-04-C-0001 and HR0011-04-C-0002). The program evaluated the impact of the microstructure on the mechanical properties.[18] The samples were subjected to a supersolvus annealing treatment in a vacuum furnace (at 1150 °C in the single γ-phase field for 30 minutes) to dissolve any existing γ¢ and then slow cooled at an average cooling rate of 24 °C/min. These samples were subsequently aged for 0, 50, and 200 hours at 760 °C in a large-chamber vacuum furnace and air quenched. For convenience, these samples will be subsequently referred to as SC0, SC50, and SC200 samples, respectively, in the remaining part of this article. The authors acknowledge the United States Air Force Research Laboratory (AFRL ISES contract, Contract No. FA8650-08-C-5226) and the United States Air Force Office of Scientific Research (AFOSR Grant No. FA9550-06-1-0193) for providing financial support for this study. In addition, the authors also gratefully acknowledge the CART at the University of North Texas (Denton, TX) and the CAMM at The Ohio State University (Columbus, OH) for access to the experimental facilities used for this study.
| Funders | Funder number |
|---|---|
| AFRL ISES | FA8650-08-C-5226 |
| Defense Sciences Office | HR0011-04-C-0001, HR0011-04-C-0002 |
| United States Air Force Office of Scientific Research | |
| United States Air Force Research Laboratory | |
| Air Force Office of Scientific Research | FA9550-06-1-0193 |
| Defense Advanced Research Projects Agency |