Joining of Powder Metallurgy Beta Gamma Titanium Aluminide Through Diffusion Brazing
Bibliographic record
Abstract
This thesis presents an experimental study of diffusion brazing powder metallurgy beta gamma titanium aluminide, along with a methodology utilizing pentenary equivalent beta forming effectiveness for the design of post bond heat treatments. Beta gamma titanium aluminides are attractive high temperature materials with low density and high specific strength. Adequate joining and repair methods, and the resultant high temperature creep performance, are fundamental requirements for the adoption of beta gamma titanium aluminides in the aerospace, automotive, and land based gas turbine industries. The developed beta forming effectiveness methodology was utilized to target composition and post bond heat treatment parameters to achieve a fully lamellar microstructure. Experimental results indicate that diffusion brazing beta gamma alloy below the eutectoid temperature of the substrate results in an 2 reaction layer at the solid/liquid interface that retards diffusion of the melting point depressant. When the brazing temperature is raised above the eutectoid temperature, the kinetics are enhanced due to the formation of a disordered phase at the solid/liquid interface resulting in complete solidification at low holding times. A step cooled post bond solutionizing heat treatment produces a fine near fully lamellar microstructure within the bond zone. Aging of the solutionized microstructure manifests interfacial 0,sec precipitates within the bond zone and parent material lamellar colonies. Intercolony 0 phase regions experience the precipitation of two previously unreported phases which do not significantly alter the microhardness across the bond zone. Creep tests conducted on the parent material reveal improved primary creep resistance and reduced rupture time with aging. Creep tests conducted on the post bond heat treated specimens reveal that high stress levels result in premature rupture due to bond-line porosity acting as sites for void coalescence. Decomposition of the intercolony 0 phase occurred during creep due to the altered composition and hence solvus temperature within the bond zone. With proper management of bond-line porosity, diffusion brazing meets or exceeds the performance of the parent material iii in the primary creep regime at low stress levels. iv To Leili and Evan. v I would like express my sincere gratitude to my two thesis supervisors Dr. Henry Saari and Dr. Dongyi Seo for giving me the opportunity to work on such an interesting research topic. I very much appreciated their
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.002 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".