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Investigating the influence of coating composition and microstructure on the potentiodynamic polarization behavior of HVAF processed coatings
University West, Department of Engineering Science.
2022 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Corrosion is a severe threat to the longevity of automotive brake discs. Typically, protective coatings of WC-CoCr composition processed by thermal spray route are applied to provide adequate wear and corrosion resistance. However, ‘Co’-containing materials are classified as carcinogenic, which compromises the health and safety of the end-users and the coating applicators. Therefore, identifying sustainable and non-toxic alternatives to the toxic, Co-containing coatings are of interest. In addition to the coating composition, microstructure of the as-deposited coatings influences their corrosion behavior. For instance, a coating with high number of defects (cracks, pores, etc.) adversely influences their corrosion performance. The coating microstructure is intimately related to the processing route employed to manufacture the coatings. High Velocity Air Fuel (HVAF) is a relatively new thermal spray processing technique that has shown the capability to deposit high quality coatings possessing excellent corrosion performance. The primary objective of this work was to assess the corrosion behavior and degradation mechanisms of the sustainable, Fe-based coatings, High Entropy Alloy (HEA) coatings, WC-Co, Cr3C2-NiCr, substrates, and compare their performance in 3.5 wt.% NaCl environment, to find the appropriate coatings, depend on the state for the future application. The secondary objective was to examine the influence of HVAF processing conditions on the microstructure and corrosion behavior of the sustainable Fe-based coatings. Therefore, potentiodynamic polarization behavior of widely employed coatings of Cr3C2-NiCr, WC-CoCr, along with the new composition-based coatings of High Entropy Alloys (HEA), and the Fe-based chemistries (Rockit-401/R-401 and FeSP586) was examined. Additionally, the effect of HVAF processing parameters on the microstructure, porosity content, potentiodynamic polarization behaviour of the Fe-based (R-401) coatings was investigated. It was shown that the Fe-based coatings with low porosity content and minimal partially undeformed splats demonstrated superior corrosion performance. A detailed SEM analysis was performed to reveal the corrosion products.  iii Furthermore, it was shown that the coatings with highest ‘Cr’-content demonstrated superior polarization resistance among the investigated coatings. Finally, the potentiodynamic polarization performance of the investigated coatings was benchmarked with the widely employed substrates of cast iron, aluminum alloy (Al-Si) and low carbon steel. This work provides an excellent framework to rank the potentiodynamic polarization of the currently used coatings, substrates and compare them with the experimental compositions of the HEA and Fe-based alloy-based coatings in 3.5 wt.% NaCl environment.

Place, publisher, year, edition, pages
2022. , p. 40
Keywords [en]
HVAF Coating, Corrosion test
National Category
Corrosion Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
URN: urn:nbn:se:hv:diva-19049Local ID: EXM902OAI: oai:DiVA.org:hv-19049DiVA, id: diva2:1687161
Subject / course
Mechanical engineering
Educational program
Masterprogram i tillverkningsteknik
Supervisors
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Available from: 2022-08-15 Created: 2022-08-14 Last updated: 2022-08-15Bibliographically approved

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