Investigating hydrogen embrittlement in aerospace martensiticsteels
Notice bibliographique
Résumé
The structural integrity of aerospace components depends on material composition and the ability to withstand harsh and aggressive environments without much degradation under heavy loading conditions. Landing gears are essential components used in the aerospace industry which are typically made from high-strength martensitic steels. SAE 4340 steel is commonly used in the manufacture of landing gears due to the combined properties of high strength and toughness. However, this grade of steel can become brittle during service in an environment which can expose it to hydrogen embrittlement (HE). On the other hand, steel grades like 300M are promising alternatives to withstand heavy loads and resist HE. Therefore, there has been a recent drive in the aerospace industry to select which steel grade is more suitable to withstand HE in harsh environment. In this work, the response and resistance to HE of these two high-strength martensitic steels for aerospace applications were studied using electrochemical hydrogen permeation and small-scale shear punch mechanical testing techniques. First, circular disc samples (13 mm diameter, 0.6 mm thickness) of both 4340 and 300M were prepared from annealed steel bars in batches of 10 and subjected to heat treatments to obtain tempered martensitic steel microstructures conforming to the industry standards used for the manufacturing of landing gears. Next, the heat-treated and surface-polished disk samples were electrolytically charged with hydrogen using a DevanathanStachurski double-cell set up at different current densities to simultaneously examine the hydrogen diffusivity. Shear punch experiments were then performed to investigate the difference in ductility reduction and strength loss between the hydrogencharged and uncharged samples for the two steel types (4340 and 300M). Further investigations into the failure modes of the punched discs due to HE were conducted using SEM and EBSD characterization techniques. The results of the electrochemical hydrogen permeation curves show that 300M had lower hydrogen diffusivity than 4340. This indicates that 300M prevents easy diffusion of hydrogen through its microstructure compared to 4340 and likely reduces the amount of diffusible hydrogen into critical areas containing defects. Consequently, the shear punch test results show that 300M outperforms 4340 in terms of strength loss and reduction in ductility. With regard to the type of failure, mostly shear-ductile dimples were observed in uncharged specimens. On the other hand, brittle-like fracture surfaces and some secondary cracking were observed in hydrogen-charged punched steels, while 4340 experienced more severe damage when charged with hydrogen at a higher current density compared to the mechanical response of 300M.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| 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) | 0,001 | 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 découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».