Porcelain enamel coatings, from the past to the future: solved and unsolved issues for the improvement of their mechanical properties

Porcelain enamel coatings have their origins in ancient times when they were mainly used for decorative and ornamental purposes. From the industrial revolution onwards, these coatings have started to be used also as functional layers, ranging from home applications up to the use in high-technological fields, such as in chemical reactors. The excellent properties of enamel coatings, such as fire resistance, protection of the substrate from corrosion, resistance to atmospheric and chemical degradation, mainly depend and originate from the glassy nature of the enamel matrix itself. On the other side, the vitreous nature of enamel coatings limits their application in many fields, where mechanical stress and heavy abrasion phenomena could lead to nucleation and propagation of cracks inside the material, thus negatively affecting the protective properties of this coating. Many efforts have been made to improve the abrasion resistance of enamelled materials. On this regard, researchers showed encouraging results and proposed many different improvement approaches. Now it is possible to obtain enamels with enhanced resistance to abrasion. Differently, the investigation of the mechanical properties of enamel coatings remains a poorly studied topic. In the literature, there are interesting methodological ideas, which could be successfully applied to the mechanical study of enamelled materials and could allow to have further insights on their behaviour. Thus, the path that should be followed in the future includes the mechanical characterization of these coatings and the search for new solutions to address their brittle behaviour.