Innovative Emailbeschichtungen mit verbesserten mechanischen Eigenschaften durch Zusatz von Graphen und Edelstahl

The development of environmental friendly materials with improved functional properties can be achieved using new technologies but also by exploiting the modification of already-existing materials, that can be adapted for specific high-duty technological applications. Vitreous enamel is an inorganic material, usually deposited on metal substrates for corrosion-protection purposes. Regarding metal substratematerials, aluminium alloys are increasingly used in many applications as they represent a good compromise betweenstrength and lightweight, but they are susceptible to corrosion in environments with very low or high pH values. Vitreous enamel coatings could be a valid solution to overcome these issues and improve the durability of aluminium-based components. From a mechanical point of view, enamel coatings are characterized by a non-excellent abrasion resistance and high susceptibility to tensile stresses, as the whole mechanical performances are dominated by the brittle-prone fracture behaviour of the enamel matrix. Abrasive wear is a very common degradation mechanism for enamelled materials as it can lead to the deterioration of surface aesthetical properties and to a loss of chemical resistance and protective properties. Tensile stresses are also detrimental for the durability of enamelled artifacts, as the nucleation and propagation of through-thickness cracks negatively affect the corrosion protection properties of these coatings, as the covered metal meets the external aggressive environment, leading to catastrophic corrosion phenomena. Thus, it is necessary to improve the mechanical properties of enamel coatings with a particular focus on abrasion resistance and fracture toughness (cracking resistance), exploiting one of the following approaches: the addition of mill additives [3], the addition of hard ceramic particles (HCPs) [4], the addition of self-lubricant additives (such as graphene NPs) [5], or the addition of metallic lamellar powders. Many studies are present in the literature about the improvement of enamel’s abrasion resistance by the addition of HCPs, but many issues about the agglomeration of the particles and the influence of their shape on the creation of weak stress points are highlighted. Thus, the authors focused their attention on the efficacy of self-lubricating agents (graphene nanoplatelets) and metallic lamellar powders (316L stainless steel flakes). Graphene is a two-dimensional material with excellent electrical, mechanical, and self-lubricant properties, which has been extensively used in the development of composite polymeric and ceramic materials. Stainless steel lamellar powders are also an interesting material for the fabrication of composite materials and coatings, as they are appreciated for their ability to withstand mechanical stresses by ductile deformation. The use of metallic powders in brittle matrix composites is not so common in the literature, but it is supposed to be an effective approach for the creation of tougher composites.