Abrasion resistance of vitreous enamel coatings in function of frit composition and particles presence

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. Enamel presents optimum corrosion protection and high hardness values but the low fracture toughness reduces its resistance to abrasive wear related to brittle fracture. The microstructure of enamel, the chemical composition of the frit, and the deposition parameters are crucial for the final properties. Moreover, it is possible to introduce mill additives in the frit or hard particles inside the layers to improve final resistance. In this paper, abrasion resistance of enamel is tested by Taber Abraser test. Mill additives (spodumene or quartz), hard (WC or SiC) or solid lubricant (graphite) particles have been added to the frit to study their influence on the abrasion resistance. The abrasion resistance of modified enamels was evaluated through mass loss after abrasion and wear track were observed by SEM in order to evaluate the abrasion damage. An improvement of the abrasion resistance was obtained modifying the frit with mill additives. The introduction of SiC and WC particles produced an important modification in wear mechanism of the glassy coating, reducing the crack nucleation due to the low pores quantity and good interface between vitreous matrix and particles. In these cases the wear mechanism is limited to scratches on the surface.