TRIBOLOGICAL PROPERTIES OF RF-SPUTTERED TITANIUM-BASED HARD COATINGS AND THEIR BEHAVIOR UNDER PLASTICS-PROCESSING CONDITIONS

Owing to the use of abrasive fillers and corrosive components in plastics, wear appears on plastics-processing equipment. As shown previously, TiN coatings offer high wear resistance in other tribological systems. Therefore it seems obvious to use TiN coatings for wear reduction in plastics processing. This paper deals with titanium-based hard coatings. The coatings were deposited on steel substrates by means of an r.f. sputter process with r.f. substrate bias. The coatings were tested with regard to their fundamental properties such as hardness, adhesion and coating structure. An increased substrate bias voltage leads to higher hardness and a denser coating structure. The optimum of adhesion and cohesion of the coatings is found in the range from -20 to -50 V. The wear behaviour of the coatings under plastics-processing conditions was investigated by two model wear tests corresponding to the tribological systems inside a screw-barrel system. For the melting zone a remarkable improvement in wear resistance was achieved.