Composite vitreous enamel coatings with the addition of 316L stainless steel flakes: Novel insights on their behaviour under mechanical stresses

Vitreous enamel coatings are greatly appreciated for their ability to protect the covered metals from weathering and corrosion. On the other side, their applicability is somehow limited, as they show brittle behaviour when they are subjected to mechanical stresses. The addition of a second ductile phase inside a brittle matrix, thus the creation of a composite material, is known to be an effective way to improve the fracture toughness and cracking resistance of brittle materials and coatings. The main aim of this research work is to deeply characterize the mechanical properties of composite 316-L stainless steel flakes/enamel coatings under different mechanical solicitations, in particular performing 4-point bending tests, indentation fracture tests, and scratch tests. Three different sample typologies are taken under consideration for these tests: the reference sample without the addition of metallic flakes, the sample with 1 wt% of 316L steel flakes, and the sample with 5 wt% 316L steel flakes. The mechanical behaviour of the samples is compared, and the damaging mechanisms are always clarified by means of optical and scanning electron observations. The addition of 5 wt% stainless steel flakes resulted to be useful in improving the cracking resistance of the coatings and in limiting the extent of cohesive damage.