Isochronal Phase Transformation in Bimodal Ti-55531
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Dilatometric Behaviors
3.2. Microstructure Observation
3.3. Phase Identification
4. Discussion
5. Conclusions
- Only β → αacicular transformation took place at 678 K, and the αglobular was not involved. When heated up to 788 K, α → β transformation occurred. The α → β phase transformation included two stages; αacicular → β and αglobular → β transformations dominated in different temperature ranges. The dissolution of αacicular terminated before the start of αglobular dissolution.
- The expansion/contraction behaviors in the dilatometry test were the thermal presentations of phase transformation. α precipitation was associated with expansion due to the increase of α volume. The expansion in the dissolution of α was associated with the synergetic effect of thermodynamics and kinetics on elements partitioning between α and β phases.
- The dissolution of α was affected by the morphology. The average activation energy for αacicular → β transformation was 176.58 kJ/mol, while that of the αglobular → β transformation was 269.65 kJ/mol in the Ti-55531 alloy. The differences in activation energy and rate originated from the difference in the chemical composition and interface curvature between two α phases.
Author Contributions
Funding
Conflicts of Interest
References
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Element | wt. % | at. % | Type | |
---|---|---|---|---|
Major | Ti | Balance | - | |
Component | Al | 5.20 | 9.16 | α-stabilizer |
Mo | 4.92 | 2.44 | β-stabilizer | |
V | 4.96 | 4.63 | β-stabilizer | |
Cr | 2.99 | 2.73 | β-stabilizer | |
Zr | 1.08 | 0.56 | neutral element | |
Trace element | Fe | 0.402 | 0.34 | - |
Si | 0.078 | 0.13 | - | |
O | 0.075 | 0.22 | - | |
N | 0.005 | 0.02 | - | |
H | 0.001 | 0.05 | - |
Temperature (K) | Globular α | Acicular α | Total α Fraction from SEM (vol. %) | Total α Fraction from XRD (vol. %) | |||
---|---|---|---|---|---|---|---|
Average Diameter (μm) | Volume Fraction (vol. %) | Average Length (μm) | Average Width (μm) | Volume Fraction (vol. %) | |||
298 | 1.49 ± 0.10 | 27.02 ± 1.84 | 0.097 ± 0.018 | 0.050 ± 0.008 | 24.48 ± 1.69 | 51.49 ± 2.53 | 52.65 |
678 | 1.47 ± 0.10 | 27.35 ± 1.68 | 0.098 ± 0.021 | 0.047 ± 0.007 | 24.23 ± 1.72 | 51.58 ± 2.25 | - |
756 | 1.43 ± 0.11 | 28.98 ± 1.76 | 0.146 ± 0.029 | 0.061 ± 0.008 | 24.98 ± 1.86 | 53.95 ± 2.01 | - |
788 | 1.46 ± 0.10 | 28.08 ± 1.92 | 0.202 ± 0.024 | 0.073 ± 0.006 | 26.41 ± 1.54 | 54.49 ± 1.93 | 56.98 |
892 | 1.46 ± 0.10 | 27.78 ± 1.65 | 0.175 ± 0.017 | 0.068 ± 0.009 | 24.84 ± 1.60 | 52.62 ± 2.25 | 54.37 |
938 | 1.50 ± 0.10 | 28.48 ± 1.47 | 0.147 ± 0.019 | 0.061 ± 0.008 | 12.73 ± 1.01 | 41.21 ± 1.87 | - |
975 | 1.45 ± 0.11 | 28.08 ± 1.03 | - | - | - | 28.08 ± 1.03 | - |
990 | 1.39 ± 0.90 | 23.80 ± 1.01 | - | - | - | 23.80 ± 1.01 | - |
1038 | 0.46 ± 0.03 | 4.63 ± 0.67 | - | - | - | 4.63 ± 0.67 | 6.83 |
1123 | - | - | - | - | - | - | - |
Temperature Range | Selected Characteristic Temperatures | Dilatometric Behavior | Observed Phase Transformation |
---|---|---|---|
678–788 K | 678, 756, 788 K | Expansion | β → αacicular |
788–975 K | 892,938, 975 K | Expansion | αacicular → β |
975–1104 K | 990, 1038 K | Expansion | αglobular → β |
>1104 K | 1120 K | Ending platform | Full β state |
H (K/min) | Acicular α dissolution Tp1 (K) | Globular α dissolution Tp2 (K) |
---|---|---|
1 | 892 | 1035 |
3 | 926 | 1069 |
5 | 946 | 1088 |
8 | 969 | 1100 |
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Chen, F.; Xu, G.; Zhou, K.; Chang, H. Isochronal Phase Transformation in Bimodal Ti-55531. Metals 2019, 9, 790. https://doi.org/10.3390/met9070790
Chen F, Xu G, Zhou K, Chang H. Isochronal Phase Transformation in Bimodal Ti-55531. Metals. 2019; 9(7):790. https://doi.org/10.3390/met9070790
Chicago/Turabian StyleChen, Fuwen, Guanglong Xu, Kechao Zhou, and Hui Chang. 2019. "Isochronal Phase Transformation in Bimodal Ti-55531" Metals 9, no. 7: 790. https://doi.org/10.3390/met9070790