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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Notice bibliographique
Résumé
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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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle