Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Chemistry and Hardness
3.2. Microstructure
3.3. X-ray Diffraction
4. Discussion
5. Conclusions
- Processing of Alloy 718 powder under both argon and nitrogen resulted in the nitrogen loss of about 25% (≈400 ppm) in comparison to the feedstock powder. High-purity nitrogen led to a slightly reduced nitrogen loss from the powder to the deposited material, with about 50 ppm (5%) higher N2 compared to the material produced under argon. This is explained by the increased nitrogen solubility for higher nitrogen partial pressure as calculated with Thermo-Calc.
- Using both high-purity argon and nitrogen led to about 30% loss in oxygen compared to the powder feedstock. Reducing the residual oxygen in the process atmosphere from 500 to 50 ppm during L-PBF processing resulted only in a slight decrease in the oxygen content in the part in the range of 10 to 30 ppm O2.
- Micron-sized nitrides and Al-rich oxide inclusions and their clusters were observed throughout the samples cross-sections, and their origin was confirmed to be connected to the virgin powder, where similar features were observed as well. The transfer of these inclusions is connected to their high melting temperature and thermodynamic stability, leading to their conservation along the process chain.
- Preferential accumulation of nitrides and oxide inclusions was observed on the top surfaces close to the scan track edges, confirming their re-distribution during L-PBF processing along the specimen height.
- Kinetic calculations confirm limited changes in nitride size observed between the powder and the produced samples, as the precipitation of nitrides was shown to be insignificant for the cooling rate of 10 K/s, which is several orders of magnitude lower than that typically experienced by the L-PBF deposited material (107 K/s), and hence, nitride precipitation during L-PBF processing can be neglected.
- The small differences in composition between the samples produced under argon and nitrogen did not impact their Vickers hardness. Further assessment of the mechanical properties of the produced material, at room and elevated temperatures after post heat treatment, is recommended to fully understand the potential effect of the applied processing atmospheres.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Gas | O2 level | O (ppm) | N (ppm) | HV1 |
---|---|---|---|---|
Argon | 500 ppm O2 | 316 ± 38 | 1091 ± 43 | 333 ± 8 |
Argon | 50 ppm O2 | 303 ± 30 | 1099 ± 39 | 332 ± 4 |
Nitrogen | 500 ppm O2 | 329 ± 39 | 1142 ± 30 | 334 ± 3 |
Nitrogen | 50 ppm O2 | 293 ± 24 | 1148 ± 32 | 331 ± 8 |
Virgin powder | N.A. | 472 ± 13 | 1495 ± 4 | N.A. |
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Pauzon, C.; Markström, A.; Dubiez-Le Goff, S.; Hryha, E. Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion. Metals 2021, 11, 1254. https://doi.org/10.3390/met11081254
Pauzon C, Markström A, Dubiez-Le Goff S, Hryha E. Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion. Metals. 2021; 11(8):1254. https://doi.org/10.3390/met11081254
Chicago/Turabian StylePauzon, Camille, Andreas Markström, Sophie Dubiez-Le Goff, and Eduard Hryha. 2021. "Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion" Metals 11, no. 8: 1254. https://doi.org/10.3390/met11081254