Ömer Furkan ÖTKEN, BSc. Student
Metallurgical and Materials Engineering
Yıldız Technical University
Development of Wear Resistant Vitreous Enamel Coating
Co-Supervisor: Nurullah Çöpoğlu, Yasin Bozkurt Yılmaz
Vitreous enamel is an inorganic coating applied on metallic substrates as powder and fired at relatively high temperature in order to cover the surface forming the coating. This kind of layer shows, at the same time, very good functional and aesthetical properties. In several applications, good mechanical resistance together with corrosion protection is required and enamel is a good alternative to other coatings . An enamel coating has outstanding properties such as extreme hardness, high temperature and thermal shock resistance, chemical inertness, anti-corrosion, anti-oxidation, and resistance to abrasion and scratching . Enamel can be applied both on steel and cast iron substrates. Steel components, such as water heaters, electrical appliances, chemical plants and road infrastructure parts are extensively protected using this type of coatings, in particular where high durability is required. The application of enamel-coating technology in cast-iron overflow components has been reported, including many hydraulic pieces of equipment, such as pumps, pipes, and turbine blades [3-4]. Independently on the substrate, enamel coatings show excellent durability, but from a mechanical point of view impact and abrasion resistance is not optimal despite the good hardness values of the coating because of its glassy nature and therefore its brittleness . Abrasion is a very common mechanism of degradation of enameled surfaces. Any mechanism where the hard asperities or particles of one surface cause damage to the surface in contact under respective motion can be defined as abrasion. The damage that they produce can be of two general types: material deformation or particles formation with material removal. As common for brittle material, the wear and abrasion resistance of enamels decreases by increasing the hardness value, since under loaded conditions fracture may occur and propagate [6-7]. By abrasion enameled surface can lose their surface glassy layer, leading to open the intrinsic porosity and reducing so the chemical resistance and durability. Moreover, if cracks propagate to the interface with the substrate corrosion protection is also negatively affected. It is possible to introduce mill additives in the frit or hard particles inside the layers to improve final resistance. It is demonstrated that nanoparticles used as additives for different ceramic matrices, typically silicon carbide (SiC), silicon dioxide (SiO2), aluminium oxide (Al2O3), zirconium silicate (ZrSiO4), zirconium diboride (ZrB2), boron carbide (B4C), tungsten carbide (WC), titanium diboride (TiB2), calcium hexaboride (CaB6), zirconium dioxide (ZrO2) or titanium dioxide(TiO2), provide an enhancement of mechanical properties, mainly in wear resistance .
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