The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting
Abstract
:1. Introduction
2. Materials and Experimental Procedure
Design of Post-Processes
3. Results
3.1. Microstructure Changes
3.1.1. The As-Built Microstructure
3.1.2. The Heat-Treated Microstructure
3.1.3. The HIPed Microstructure
3.2. Mechanical Properties of Heat-Treated SLM Specimens
3.3. Mechanical Properties of HIPed SLM Specimens
4. Discussion
4.1. Effects of the Formation of Laves Phase/δ Phase in SLM Materials
4.2. Grain Morphologies of the As-Built Specimen
4.3. Inhomogeneous Grain Growth and Its Effects on Mechanical Properties
4.4. The Effects of HIP on the Mechanical Properties of SLM Specimens at 650 °C
5. Conclusions
- The dendrite structure and interdendritic regions were decorated with a continuous network of Laves phase and carbides in the as-built specimen. In addition, the rapid heating and cooling induces thermal variations that cause high-density dislocations.
- The originally recommended heat treatment process, STA-980 °C, for cast and wrought materials is not effective in SLM-processed specimens.
- Laves phases/δ phases were dissolved in the matrix by a solution treatment at higher temperatures; however, creep properties were not improved greatly because of the inhomogeneous grain growth.
- The HIPed materials exhibited a serrated grain boundary with a high-volume fraction of carbide along the grain boundary. HIP improved the creep life, and the HIP+ direct aging process was the most effective among the post-processes for improving the creep behavior at 650 °C.
Author Contributions
Funding
Conflicts of Interest
References
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Cr | Nb | Mo | Ti | Al | Co | Cu | C | Si, Mn | P, S | B | O | Fe | Ni |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
19.6 | 5.05 | 2.85 | 1.10 | 0.46 | 0.03 | 0.05 | 0.04 | 0.04 | 0.0 | 0.002 | 0.019 | Balance | 52.59 |
Variant | 1st Step: Solution Treatment | 2nd Step: Age Hardening |
STA-980 °C | 980 °C/1 h/air cooling | 720 °C/8 h/furnace cooling to 620 °C + 620 °C/10 h/air cooling |
STA-1045 °C | 1045 °C/1 h/air cooling | |
STA-1065 °C | 1065 °C/1 h/air cooling | |
STA-1120 °C | 1120 °C/1 h/air cooling | |
STA-1180 °C/1 h | 1180 °C/1 h/air cooling | |
STA-1180 °C/4 h | 1180 °C/4 h/furnace cooling | |
Variant | 1st Step: HIP Process | 2nd Step: Post-Treatment |
As-HIPed | HIP at 1180 °C/175 MPa/4 h | N/A |
HIP + direct aging | HIP at 1180 °C/175 MPa/4 h | 720 °C/8 h/furnace cooling to 620 °C + 620 °C/10 h/air cooling |
Variant | Density (g/cm3) | Density Compared with Cast and Wrought Alloy (%) |
---|---|---|
cast and wrought alloy | 8.23 | 100.00 |
as-built | 8.20 | 99.62 |
STA-980 °C | 8.19 | 99.46 |
STA-1045 °C | 8.17 | 99.26 |
STA-1065 °C | 8.20 | 99.59 |
STA-1120 °C | 8.18 | 99.38 |
STA-1180 °C/1 h | 8.20 | 99.61 |
STA-1180 °C/4 h | 8.18 | 99.32 |
as-HIPed | 8.19 | 99.45 |
HIP+ direct aging | 8.24 | 100.11 |
Elements | Al | Ti | Cr | Fe | Ni | Nb | Mo |
---|---|---|---|---|---|---|---|
Laves (as-built) | 2.20 | 1.09 | 12.74 | 11.28 | 45.42 | 22.06 | 5.21 |
δ phase (STA-980 °C) | 0.84 | 2.43 | 4.17 | 3.41 | 51.16 | 35.86 | 2.12 |
matrix (STA-980 °C) | 2.38 | 0.47 | 12.45 | 14.16 | 61.63 | 5.59 | 3.20 |
Variant | STA-980 °C | STA-1045 °C | STA-1065 °C | STA-1120 °C | STA-1180 °C/1 h | STA-1180 °C/4 h | As-HIPed | HIP+ Direct Aging |
---|---|---|---|---|---|---|---|---|
steady-state rate, έ (10−7 s−1) | 10.7 | 1.59 | 1.90 | 1.59 | 1.37 | 1.74 | 1.73 | 0.89 |
creep life (h) | 134 | 254 | 426 | 230 | 462 | 151 | 493 | 677 |
strain (%) | 1.29 | 0.56 | 0.53 | 0.75 | 0.81 | 0.2 | 1.10 | 0.65 |
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Kuo, Y.-L.; Nagahari, T.; Kakehi, K. The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting. Materials 2018, 11, 996. https://doi.org/10.3390/ma11060996
Kuo Y-L, Nagahari T, Kakehi K. The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting. Materials. 2018; 11(6):996. https://doi.org/10.3390/ma11060996
Chicago/Turabian StyleKuo, Yen-Ling, Toshiki Nagahari, and Koji Kakehi. 2018. "The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting" Materials 11, no. 6: 996. https://doi.org/10.3390/ma11060996
APA StyleKuo, Y. -L., Nagahari, T., & Kakehi, K. (2018). The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting. Materials, 11(6), 996. https://doi.org/10.3390/ma11060996