Name: Juliana Souza de Oliveira
Type: MSc dissertation
Publication date: 18/10/2021

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Examining board:

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Marília Mendonça de Lima External Examiner *
Ivandro Bonetti External Examiner *
Cherlio Scandian Internal Examiner *

Summary: Demands for higher performance in industrial applications leads to technological development for wear and corrosion materials protection. The use of superior mechanical and tribological properties coatings on a lower cost substrate is an economically attractive solution. Thermally sprayed coatings stands out for the use of composite materials in high wear resistance systems. At this work, FeNbC coatings deposited on SAE 1020 steel by powder oxyacetylene flame spray process are analyzed. The parameters variation of powder granulometry, spray distance, feed rate and substrate preheating on thermal spraying resulted in nine study conditions. Optical and scanning electron microscopy analyzes showed the coating heterogeneous microstructure, characterized by splats with pores, cracks and oxides between layers. Coatings cross-section Vickers microhardness tests resulted in high hardness, especially at the samples with higher oxide contents. Knoop indentations test was used to evaluate the Young’s modulus, which showed the fragile feature coatings. Vickers microindentation tests allowed to evaluate the fracture toughness wich presented values between 1.52 and 2.52 MPa√m. The coating/substrate adhesion and the cohesion between splats were evaluated by coating cross-section scratch test. The thicker coatings also showed greater adhesion. Ball cratering tests with SiO2 abrasive slurry was used to evaluate abrasive wear resistance. Worn sufaces scanning electron microscopy images showed a dominant grooving wear micromechanism. Microindentations at wear grooves suggests a rolling wear secondary micromechanism. Lower hardness coatings also showed the lowest abrasive wear resistance.

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