Advancement of Compositional and Microstructural Design of Intermetallic γ-TiAl Based Alloys Determined by Atom Probe Tomography
Abstract
:1. Introduction
2. Atom Probe Tomography
2.1. Background of Technique: Principles of Method and Compositional Measurements
2.2. The Local Electrode Atom Probe
2.3. Methods of Specimen Preparation
3. Effects of Alloying Elements
3.1. Niobium and Molybdenum: Phase Formation, Phase Preference and Phase Stability
3.2. Boron Addition and Boride Formation
3.3. The Formation of ωo Phase
3.4. Enhancement of the TNM Alloying Concept: Effects of Carbon Addition
4. Characterization of Nano-Scaled Lamellar Structures: Effects of Silicon Addition
5. Conclusions
- The chemical composition of all constituent phases (γ, α2, βo) of a TNM alloy was determined. Preferential partitioning of Nb and Mo to the βo phase is discernable and the α2 phase shows the highest impurity levels. The element B is mainly present in mono-borides.
- Within the βo phase the precipitation of a further minor phase, the so-called ωo phase, can be detected, which is depleted in the strong β-stabilizing element Mo.
- Carbon, if alloyed to TNM alloys, preferentially resides in the α2 phase, followed by the γ phase. The βo phase appears to be completely depleted of C. In the microstructural condition investigated both α2 and γ phase are significantly strengthened by solid solution hardening due to the presence of the interstitial element C. However, the βo phase seems to soften by the addition of C, which stems from the fact that the presence of C yields a lower βo phase fraction, thereby increasing the Mo content in this phase, which in turn results in the suppression of the ωo phase formation and its concomitant hardening effects. Carbon, moreover, tends to segregate to interfaces, which may result in lower interface mobilities, thus, stabilizing the microstructure.
- In ultra-fine lamellar structures, Si preferentially occupies the α2 phase, whereby neither interfacial segregation nor interfacial precipitation is observed in TNM+ alloys, in contrast to other TiAl alloying systems, which is due to a substantial fraction of α2 phase where Si is substitutionally dissolved.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Alloy | Element Concentration (at%) | |||||
---|---|---|---|---|---|---|
B | Ti | Al | Nb | Mo | Other | |
TIA-20 [91] 1 | 52.0 ± 3.2 | 46.3 ± 3.2 | 0.4 ± 0.4 | 1.2 ± 0.7 | - | 0.1 |
TNM (present study) | 45.1 ± 0.01 | 47.0 ± 0.01 | - | 6.8 ± 0.03 | 1.1 ± 0.04 | 0.0 |
Phase | Element Concentration (at%) | ||||||
---|---|---|---|---|---|---|---|
Ti | Al | Nb | Mo | C | Si | Other | |
γ | 49.8 ± 0.02 | 44.8 ± 0.02 | 4.01 ± 0.03 | 0.85 ± 0.03 | 0.16 ± 0.03 | 0.21 ± 0.02 | 0.17 |
α2 | 61.4 ± 0.03 | 32.1 ± 0.05 | 3.90 ± 0.05 | 1.14 ± 0.06 | 0.35 ± 0.06 | 0.51 ± 0.06 | 0.60 |
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Klein, T.; Clemens, H.; Mayer, S. Advancement of Compositional and Microstructural Design of Intermetallic γ-TiAl Based Alloys Determined by Atom Probe Tomography. Materials 2016, 9, 755. https://doi.org/10.3390/ma9090755
Klein T, Clemens H, Mayer S. Advancement of Compositional and Microstructural Design of Intermetallic γ-TiAl Based Alloys Determined by Atom Probe Tomography. Materials. 2016; 9(9):755. https://doi.org/10.3390/ma9090755
Chicago/Turabian StyleKlein, Thomas, Helmut Clemens, and Svea Mayer. 2016. "Advancement of Compositional and Microstructural Design of Intermetallic γ-TiAl Based Alloys Determined by Atom Probe Tomography" Materials 9, no. 9: 755. https://doi.org/10.3390/ma9090755