FUNDAMENTAL AND TRIBOLOGICAL PROPERTIES OF R F SPUTTERED TIN COATINGS IN PLASTIC MANUFACTURING MODEL WEAR TESTS

In plastic manufacturing an increasing content of abrasive particles and corrosive components in combination with working temperatures up to 450-degrees-C have led to a new dimension of wear. As shown in previous work, TiN coatings have been wear resistant under corrosive conditions and elevated temperatures. In this paper we deal with thin hard TiN coatings deposited onto 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 structure. An increased substrate bias voltage up to -100 V leads to higher hardness values and a more dense coating structure. Adhesion and cohesion of the coatings are best in the range from -30 V to -50 V. The wear behaviour of the coatings under plastic manufacturing conditions was investigated by two model wear tests. Corresponding to the conveying and the melting zones of screw barrel systems the test pieces were subject to abrasive and abrasive-corrosive wear under elevated temperatures. It is shown that the combination of high hardness, dense structure and good adhesion leads to superior wear behaviour of r.f. bias sputtered TiN coatings. For the melting zone model wear test a remarkable improvement in wear resistance by a factor of more than 10 was achieved.