Abstract: Hot working steels have been used as die materials for hot extrusion of aluminium.Due to tribological interaction at elevated temperature between the die bearing and thesurface of extruded aluminium profiles, not only the surface quality of the extrudedproduct, but also the lifetime of the dies decreases. Deposition of TiBN hard films onthe die bearing could improve the die performance. Treatment should be done in aduplex process process combining a plasma nitriding pretreatment (PN) and a plasmaassisted chemical vapour deposition (PACVD) of TiBN. In this study the influence ofthe process conditions on the properties of the duplex coatings was investigated. Therelationship between structure and mechanical property was researched. For testingthese TiBN hardfilms under elevated temperature conditions and for comparison withother possible coatings special extrusion dies with different coated bearings were used.The extrusion trials were performed on the 8MN-extrusion press at the research anddevelopment center for extrusion, Technical University of Berlin.

Key words: hard film, plasma nitriding, duplex process, PN, PACVD and extrusion