Evolution of Microstructure and Properties of Cold-Sprayed Copper Coatings: Influence of Feedstock Powder Characteristics, Process Parameters and Heat Treatment
Notice bibliographique
Résumé
The Nuclear Waste Management Organization of Canada (NWMO) uses copper coatings to protect nuclear waste containers (used fuel containers - UFCs) from corrosion in deep geological repositories (DGRs). One fabrication method is cold spray, a solid-state powder consolidation technique that enables the deposition of high-strength, dense, thick coatings at high rates. However, as-sprayed (AS) coatings are often brittle, with mechanical properties strongly dependent on process parameters and feedstock powder characteristics, including the particle-to-critical velocity ratio (η) and surface oxide content. Their response to heat treatment is also influenced by their state in the AS condition.Particle size strongly affects the η ratio, as it is inversely proportional to both particle and critical velocity. This thesis investigates the effect of copper powder size distributions on the evolution of mechanical strength and ductility in fabricated coatings.First, coatings were fabricated by cold spraying copper powders with similar characteristics (morphology, oxygen content) but different size distributions (“fine” and “coarse”) at various particle velocity ranges. Increasing η improved interparticle bonding, enhancing the mechanical properties. However, coatings originating from the “fine” powder exhibited superior strength and ductility over “coarse” powder coatings, despite attaining similar η ratios. This was attributed to the presence of thick surface oxides on the “coarse” powder particles, which were entrapped at the particle-particle interfaces (PPIs) significantly limiting metallurgical bonding.Next, coatings with varying AS properties and/or feedstock powder particle size distributions were heat-treated in identical conditions. Interparticle bonding and properties improved overall due to sintering and interparticle oxide changes. However, coatings with initially superior AS properties did not always retain their advantage post-heat treatment, as the “as-sprayed” microstructure played a key role, with coarse particle size and thick interparticle oxides being found to be detrimental.The final chapter focuses on the technique used for the mechanical property evaluation, shear punch testing. As sprayed and heat-treated coatings, along with bulk copper specimens, were tested. Insights into effective ductility and fracture behavior of copper during testing are provided. Additionally, the expected mechanical property trends for differently processed bulk and coating copper samples are confirmed, demonstrating that heat-treated cold-sprayed copper can behave similarly to bulk copper during mechanical loading and fracture.These findings contribute to optimizing copper cold spray for critical applications depending on mechanical properties. Through the selection of appropriate process parameters, feedstock powders and heat treatment conditions, it is possible to manufacture coatings with good structural integrity and properties that meet the required standards
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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) | 0,000 | 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 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 ».