In-situ evaluation of the hcp to bcc phase transformation kinetics in commercially pure titanium and Ti-5Al-5Mo-5V-3Cr alloy using laser ultrasonics
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Bibliographic record
Abstract
This thesis developed and validated laser ultrasonics as an in-situ monitor of phase transformations in commercially pure titanium and Ti - 5 wt.% Al - 5 wt.% Mo - 5 wt.% V - 3 wt.% Cr (Ti-5553). Three studies (Chapters 5, 6 and 7) were performed to achieve this goal. The first study involved using finite element modeling (FEM) to simulate wave propagation through a 2-phase aggregate to understand the effects of precipitate arrangement and phase fraction on the velocity signal. The predicted ultrasound velocity depended on the geometric configuration of the microstructure and the relative size of the pulse's wavelength compared to the microstructural feature size. However, for mixtures of phases with similar elastic properties and densities (such as in α and β titanium), the possible averaging schemes produce nearly identical velocities, and thus using a rule of mixtures involving the α and β velocities was confirmed to be sufficient. The second study showed that the ultrasonic velocity is sensitive to the α → β and β → α transformations in commercially pure titanium, even though the density and elastic modulus of these two phases are very similar. Extraction of the transformation kinetics from the ultrasonic velocity does require, however, the effects of the strong starting texture and texture evolution during grain growth to be accounted for. Finally, the third study presented in Chapter 7 took Ti-5553 specimens, solutionized them to the fully β condition, and then held them for varying times at a 700 °C isotherm to monitor precipitation kinetics with LUMet. The precipitation of α grains could be monitored by using the relative change in velocity and compared to the ex-situ obtained phase fractions. While laser ultrasonics has been previously used to measure the elastic constants in Ti-H alloys and to qualitatively observe the transformation kinetics in Ti-6V-4Al the work presented here represents the first fully quantitative assessment of transformation kinetics in pure titanium via laser ultrasonics. This is a significant result since ex-situ, metallographic analysis of the transformation in commercially pure titanium is not possible as the high temperature β phase is not stable at room temperature, and it paves the way for this technique to be used for microstructure monitoring during more complex thermo-mechanical processing paths in the Gleeble thermo-mechanical simulator. Laser ultrasonics was also validated in Ti-5553, where it was used to monitor the precipitation of α precipitates during an isothermal treatment, and produced comparable kinetics to the kinetics derived from ex-situ metallography.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it