A TRIBOLOGICAL INVESTIGATION OF PHYSICAL VAPOR-DEPOSITION TIN COATINGS PAIRED WITH SURFACE-TREATED STEELS FOR MACHINE ELEMENT APPLICATIONS

Various potential surface treated materials paired with multiple catho dic arc plasma (CAP) deposition TiN coating specimens, to be used for screws and rollers, were tested on an SRV wear machine (Optimol, Germa ny) under reciprocating wear conditions. The processing parameters of the TiN coatings, including bias voltage, arc current and partial pres sure of N2, were optimized before wear testing. The polishing pre-trea tment of the substrate yielded the highest wear resistance. The indent ation test showed that adhesive strength decreased with increasing coa ting thickness. If the coating was too thin, it was easily worn throug h. The optimum coating thickness was 3 mum. It was concluded that PVD coated TiN paired with surface treated specimens possesses less wear r esistance under HD150 and base oil lubrication. Under water-based cutt ing fluid, the self-mated TiN and TiN-surface treated specimen pairs s howed no measurable wear, only surface polishing on the TiN surface. B oth are potential sliding pairs for TiN coating in machine element app lications. The wear mechanisms of TiN include local flaking of the coa ting layer at the edge of the wear scar, surface polishing and surface pitting under oil-lubricated wear. The wear mechanisms under dry wear result in a residual TiN unworn layer with or without a transferred l ayer, and the exposed substrate region covered with a transferred laye r. Suitable sliding pairs are self-mated TiN and TiN-surface treated s pecimens under cutting fluid lubrication, and carburized specimens pai red with TiN coated specimens under base oil lubrication.