Abstract
The nickel-base Alloy 617 has been considered as the lead candidate structural material for the intermediate heat exchanger (IHX) of the Very-High-Temperature Reactor (VHTR). In order to assess the long-term performance of Alloy 617, thermal aging experiments up to 10,000. h in duration were performed at 1000. °C. Subsequently, in-situ synchrotron wide-angle X-ray scattering (WAXS) tensile tests were carried out at ambient temperature. M23C6 carbides were identified as the primary precipitates, while a smaller amount of M6C was also observed. The aging effects were quantified in several aspects: (1) macroscopic tensile properties, (2) volume fraction of the M23C6 phase, (3) the lattice strain evolution of both the matrix and the M23C6 precipitates, and (4) the dislocation density evolution during plastic deformation. The property-microstructure relationship is described with a focus on the evolution of the M23C6 phase. For aging up to 3000. h, the yield strength (YS) and ultimate tensile strength (UTS) showed little variation, with average values being 454. MPa and 787. MPa, respectively. At 10,000. h, the YS and UTS reduced to 380. MPa and 720. MPa, respectively. The reduction in YS and UTS is mainly due to the coarsening of the M23C6 precipitates. After long term aging, the volume fraction of the M23C6 phase reached a plateau and its maximum internal stress was reduced, implying that under large internal stresses the carbides were more susceptible to fracture or decohesion from the matrix. Finally, the calculated dislocation densities were in good agreement with transmission electron microscopy (TEM) measurements. The square roots of the dislocation densities and the true stresses displayed typical linear behavior and no significant change was observed in the alloys in different aging conditions.
| Original language | English |
|---|---|
| Pages (from-to) | 55-62 |
| Number of pages | 8 |
| Journal | Materials Science and Engineering: A |
| Volume | 651 |
| DOIs | |
| State | Published - Jan 10 2016 |
| Externally published | Yes |
Funding
The authors are grateful to Dr. Jonathan Almer for his WAXS analysis code. This work was supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of a Nuclear Science User Facilities experiment. This work was also supported by the U.S. Department of Energy under Grants DE-FC07-07ID14819 and DOE NEUP 09-516 . The authors also want to acknowledge the support of the International Institute for Carbon Neutral Energy Research ( WPI-I2CNER ), sponsored by the World Premier International Research Center Initiative (WPI), MEXT, Japan. Alloy 617 was provided by Haynes International, inc. The FIB and TEM experiments were carried out in the Frederick Seitz Materials Research Laboratory Central Facilities, University of Illinois. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract no. DE-AC02-06CH11357 .
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Office of Science | |
| Office of Nuclear Energy | DE-FC07-07ID14819, DOE NEUP 09-516, DE-AC07-051D14517 |
| Argonne National Laboratory | DE-AC02-06CH11357 |
| Ministry of Education, Culture, Sports, Science and Technology | |
| International Institute for Carbon-Neutral Energy Research, Kyushu University | WPI-I2CNER |
Keywords
- Alloy 617
- High-temperature thermal aging
- M23C6 carbide
- Wide-angle X-ray scattering