Abstract
This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al11Ce3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al3Ni and Al11Ce3 fibers, (iii) large ternary eutectic colonies, where the binary Al3Ni and Al11Ce3 phases are alternating or intertwining within the individual, fine fibers (diameters of ∼60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al3Ni and Al11Ce3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. The alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al3Ni particles which engulf finer, more stable Al11Ce3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al3Ni and Al11Ce3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.
Original language | English |
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Article number | 142551 |
Journal | Materials Science and Engineering: A |
Volume | 833 |
DOIs | |
State | Published - Jan 26 2022 |
Funding
TW was supported by the GO! Program from Oak Ridge National Laboratory. This research was co-sponsored by the U.S. Department of Energy , Office of Energy Efficiency and Renewable Energy , Advanced Manufacturing Office and Vehicle Technologies Office Propulsion Materials Program (AP and AS ). This work made use of the Materials Characterization and Imaging Facility and EPIC facility of Northwestern University's NUANCE Center, which both receive support from the MRSEC Program ( NSF DMR-1720139) of the Materials Research Center at Northwestern University . The authors thank Dr. Amir Farkoosh (Northwestern University) for his assistance with, and discussion of, creep testing. TW was supported by the GO! Program from Oak Ridge National Laboratory. This research was co-sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office and Vehicle Technologies Office Propulsion Materials Program (AP and AS). This work made use of the Materials Characterization and Imaging Facility and EPIC facility of Northwestern University's NUANCE Center, which both receive support from the MRSEC Program (NSF DMR-1720139) of the Materials Research Center at Northwestern University. The authors thank Dr. Amir Farkoosh (Northwestern University) for his assistance with, and discussion of, creep testing.
Keywords
- Aluminum alloys
- Coarsening
- Compressive creep
- Microhardness