Ceramic coatings on non-valve metals deposited by plasma electrolysis
Notice bibliographique
Résumé
A modified plasma electrolytic oxidation (PEO) treatment has been successfully developed for the non-valve metals of Fe and Cu in electrolyte containing sodium aluminate and sodium phosphate. This process could also be termed as plasma electrolytic aluminating (PEA) since the formation of passive films mainly relies on the aluminate ions. The passive film will hinder the current flow and cause charge build-up. When a critical voltage is reached, dielectric breakdown of the passive film will ignite the sparks. X-ray photoelectron spectroscopy (XPS) analyses indicate the passive film formed on the Fe consist of FeAl2O4, which means iron substrate participated in the reaction. On the other hand, the copper substrate was not involved in the passive film formed on the Cu, which consists of Al(OH)3. The different mechanisms could be attributed to the different reduction potentials of Fe and Cu. Taguchi analyses were used to investigate the influence of selected process parameters, including the concentration of NaAlO2 in the electrolyte (C), the frequency (f) and duty cycle (δ) of the power supply. ANOVA analysis revealed that C has the most significant contribution to hardness, corrosion resistance and thickness. While f has significant influence on hardness and corrosion resistance, δ contributes significantly to the thickness. Higher frequency means shorter duration of a single discharge which leads to denser coating with higher hardness and corrosion resistance. Higher duty cycle represents the higher power input during the PEA treatment. Therefore, the coating’s thickness increased with higher duty cycle. The coating prepared on iron substrate mainly consists of Al2O3 and FeAl2O4. The hardness, polarization resistance and thermal conductivity of the coating were 822 HV, 296 kΩ·cm2 and ~0.5 W/(m·K), respectively. The low thermal conductivity comes from the mesopores, nano-grains and amorphous materials. After cyclic thermal shock tests, the coating retained its porous structure without spallation. Post-treatments like electroless nickel plating (EP) and sol-gel silica coating were applied to seal the open pores and cracks. Both the PEA-EP and PEA-SiO2 hybrid coatings could retain good corrosion resistance after immersed in sodium chloride solution for five days, while the PEA coating degraded due to pitting corrosion at these open pores and cracks. The coating deposited on pure copper consists of ceramic matrix (Al2O3 and Cu2O) embedded with Cu particles. The amount of Cu particles increased with increased coating thickness, which could be attributed to intensified plasma discharges. The hardness, polarization resistance and thermal conductivity of the coating were 1050 HV, 141.7 kΩ·cm2 and ~5.1 W/(m·K), respectively. The increased thermal conductivity could be attributed to the presence of metallic Cu. The coating has excellent wear and corrosion resistance, which might be used for wear-corrosion protection of copper alloys.
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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 ».