Investigation of PVD thin films as hydrogen barriers in aluminized press hardened steels (PHS)

Abstract The reduction of hydrogen intake of aluminized boron press hardened steel Usibor®1500 during austenitisation at 900 °C under N2 humid atmosphere has been explored by applying thin physical vapour deposition (PVD) coatings. A wide range of metallic coatings have been explored including Au, Cu, Ti, Y, Mo, W, Cr, Ni, Ni0.8Cr0.2, Ni0.4Cr0.6, Inconel 690 and stainless steel 316L as well as some nitrides WN, CrN and oxides Al2O3 and SiO2. W, Y and Ti enhance the increase of hydrogen intake, SiO2 and Al2O3 have no effect while Au, Cu, Mo, CrN, WN, Cr, Ni and NiCr alloys provide a decrease of the hydrogen ingress. The barrier effects of these coatings are discussed as a function of their thicknesses and chemical composition of the NiCr coatings. The most efficient barrier to hydrogen intake is obtained in this study for Ni0.8Cr0.2 coating with a reduction higher than 50% for an optimum coating thickness of 200 nm. The structure and the surface of the latter coating are investigated after austenitisation by a combination of techniques.