Improvement of ‘duplex’ PVD coatings for HSS cutting tools by PFPE (perfluorpolyether ‘Z-DOL’)

A high-speed steel of M2 type was hardened by ‘duplex’ technology (ion nitriding followed by TiN PVD coating). The ‘duplex’ coating was further modified by application of a PFPE (perfluoropolyether Z-DOL) layer at the surface. The tribological parameters of the coating and the changes in composition and fine (atomic level) structural characteristics of the tool surface with a multi-layered coating were investigated. A process of self-organizing occurs during the running-in stage of the wear of the cutting tool surface with the multi-layered coating. Several parallel phenomena develop during this self-organizing process: (a) tribodecomposition of the thin surface layer: (b) formation of a stable amorphous-like protective layer (of Ti–O and Ti–F types) on the tool surface. All these processes improve the wear stability during the running-in stage of wear, leading to increased tool life.