Fatigue Properties of Narrow and Wide Gap Braze Repaired Joints
Bibliographic record
Abstract
With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material, this is largely based on the results of tensile or accelerated creep tests for most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed that the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. An analysis of the fracture surfaces using a scanning electron microscope revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".