Structure and properties of PVD TiB2 coatings

For optimizing machine parts about their function and lifetime not only the design has been varied but also the materials. Where moving parts are in contact with each other, mostly only a few nanometer thick layer guarantees the function. With surface coating by PVD the properties and structure of this layer can be modified, so the use of bulk material is not necessary. This study is about the development of a hard, wear resisting TiB2 coating for lubricant-free roller bearings. Therefore several pretensions must be fulfilled, for example, no change in the surface topography of the raceways and low temperature coating process for tempered materials. Consequently all coatings were done with the Magnetron sputter ion plating (MSIP) process. For the target material a hot isostatic pressed titanium diboride plate was used. This target is electrically conductive, so that the sputtering could be done with a de plasma. Three different substrate materials were examined. These were tempered bearing steel (100 Cr 6), silicon nitride (Si3N4), and a cutting tool material (HS 6-5-2). For optimizing the coating process and adapting it to the different materials, the temperature and the bias voltage were varied. While Si3N4 and HS 6-5-2 are insensitive to the coating temperature, the temperature of the tempered 100 Cr 6 must be lower than its tempering temperature otherwise a reduction in the hardness cannot be excluded and the support of the coating is not sufficient. The coatings were characterized by their microstructure and their mechanical properties. (C) 1997 Academic Press.