THE SHEAR IMPACT-WEAR BEHAVIOR OF TI COMPOUND COATINGS

The failure behavior of Ti compound coatings was evaluated under norma l and shear impact conditions at room and elevated temperatures. Monol ayers and combined multilayers of TiAlN and TiAlCN were deposited onto high speed steel by a cathodic are ion plating process. The shear imp act loading mode was obtained by rotating the coated disk specimen at a speed of 0.8 m s(-1) under repetitive normal impact loading of 10 N using a Co-WC ball indentor with a frequency of 5 Hz. The impact resis tance under normal impact loading appeared to be higher in the order T iAlN, TiAlN/TiAlCN and TiAlCN in accordance with the adhesive strength measured by HRC indentation tests. Meanwhile the addition of shear fo rce during repetitive normal impact loading by specimen rotation reduc ed significantly the failure resistance of all the films, both at room temperature and 600 degrees C, with a change in failure mode. It was observed through progressive failure analysis with increasing repetiti ve loading cycles that the failure under shear impact loading was acce lerated owing to the promotion of crack formation as well as laminated fragmentation by increasing tensile and shear stresses at the bail tr ailing zone resulting from tracking forces during repetitive instantan eous impacting and sliding. The propensity for failure became more sev ere owing to substrate softening for all the coatings as the temperatu re increased to 600 degrees C. (C) 1998 Elsevier Science S.A.