BEHAVIOUR TO ABRASIVE WEAR OF WHITE ENAMELLED EXTRA LOW CARBON STEEL SHEETS

The demand for advanced ceramic materials for surface engineered components is growing due to the necessity of material displaying improved properties in terms of wear and corrosion resistance. In this paper the tribological behaviour of vitreous enamel coatings are investigated by the microscale abrasive wear test. Vitreous enamels, here considered, are hybrid materials and they consist of a ceramic-vitreous matrix with specific additives which are chemically dispersed. The matrix is a boron-silicate glass made by a compound of various row materials and elements within metal oxides which enhance corrosion resistance, wear resistance, mechanical strength and fracture toughness. The compound is fired at about 1300°C and cooled into cold water obtaining the so called frit. The additives are mixed and milled with the frit, via a wet or dry processes, in order to obtain the enamel base material. The deposition process for the wet base material over the metal surface consists of three phases: wet spraying deposition, drying, firing at high temperature (850°C). In the case of the dry base material the deposition process requires an electrostatic deposition phase followed by a firing step at high temperature ( 850°C). The coating process produces a composite layered structure: an external vitreous layer, the metal sheet and an intermediate layer between the coating and the substrate. The external layer consists on a ceramic-vitreous structure in which bubbles of different dimensions are uniformly distributed. The tribological performances of the vitreous enamel coating are influenced by the nature of the frit compound, by the additives and by the presence of the embedded gas bubbles. The experimental data were analysed and relation maps between tribological properties and coating structure parameters have been carried out.