Hybrid powder-suspension plasma spraying for diverse function-dependent coating architectures
Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
Suspension Plasma Spraying (SPS) is an emerging plasma spray technique which overcomes the difficulties typically associated with feeding of fine powders (submicron or nano-sized) in conventional Atmospheric Plasma Spraying (APS) to develop interesting microstructural features for varied engineering applications, such as wear resistance, corrosion/oxidation protection, thermal barrier, etc. Another breakthrough in plasma spraying pertains to the advent of systems that allow axial injection of feedstock which considerably improves thermal exchange between the plasma plume and the injected feedstock, thereby enabling substantial enhancement in deposition rates/efficiency.
The present study utilizes both the above advances in plasma spraying to demonstrate the ability to deposit various function-dependent coating architectures by sequential/simultaneous axial injection of both powder and a suspension feedstock, henceforth referred to as hybrid plasma spray. The results amply demonstrate the flexibility and versatility of the hybrid spray process for production of superior function dependent coating architectures. Sim-ultaneous injection of the two feedstocks to form composite coatings, which is the most challenging from a processing standpoint as it requires identification of a process window which is suitable for both powder and suspension, was investigated in particular detail using deposition of Al2O3-YSZ composites as a case study. Composite coating architectures produced by hybrid spraying showed good homogeneity and the microstructure of the coating was characterized by presence of multi-scale features attributable to co-deposition of powder (micron-sized Al2O3) and suspension (involving fine YSZ powder) feedstock.
In order to better understand the role of particle size and the implications of a distributed second phase on the tribological behavior of coatings, properties of the above mentioned powder-suspension hybrid coatings were also comprehensively compared with (a) Al2O3 coatings deposited using powder (b) Al2O3 coatings deposited using suspension and (c) Al2O3-YSZ coatings deposited using both constituents as suspensions. It has been observed that fine particle size of the feedstock leads to improved tribological performance of the coating in comparison with micron-sized powder feed-stock. In addition, introduction of fine second phase into conventional coating using the hybrid approach has shown significant improvement in tribological response of the conventional coatings. However introduction of fine second phase in a fine structured coating matrix showed negligible effect on the tribological response of the coating.
Place, publisher, year, edition, pages
2016. , 49 p.
Coating, suspension plasma spray, axial injection, hybrid, layered, composite, functionally graded, tribology
IdentifiersURN: urn:nbn:se:hv:diva-9832Local ID: EXP800OAI: oai:DiVA.org:hv-9832DiVA: diva2:956514
Subject / course