In-situ characterization of the damage evolution in thin polyelectrolyte films on TWIP steel substrates

Steels showing twinning-induced plasticity (TWIP) are characterized by extraordinary mechanical properties at room temperature, i.e. high strength and ductility. But at the same time these steels are suffering from environmental effects, leading to surface corrosion and hydrogen related effects. Traditional coatings such as zinc layers may not show sufficient formability, so that local failure of these coatings can occur during forming of sheets, e.g. by deep drawing. Local failure of the coating system will eventually lead to localized corrosive attack, deteriorating the TWIP steel performance. In order to protect the surfaces during processing, a new kind of extremely formable coating for TWIP steels is proposed in this study. Thin polyelectrolyte films are deposited on the TWIP surfaces by a dip coating process. Different film conditions are established and the corresponding damage evolution is characterized. In order to precisely determine the reasons for local film cracking, a thorough characterization of the deformation behavior and the surface evolution of the TWIP steel substrates have been conducted and the suitability of the polyelectrolyte-based coatings for future applications has been demonstrated.