THE EFFECT OF ARC ION PRE-BOMBARDMENT ON THE IMPACT FAILURE OF TIN COATING ON CO-WC

Co-WC is increasingly used for precision dies and punches in semicondu ctor assembly process. The enhancement of impact resistance of hard la yer coatings on Co-WC dies and punches is crucial for the application of hard coatings such as TiN. In this study, Co-WC has been deposited with a TiN film after Ti bombardment at various bias voltages of 0-750 V using the cathodic are ion plating process. The surfaces' etching m orphology and the temperature increase upon pre-bombardment with Ti io n onto Co-WC were evaluated by SEM and in-situ monitoring, respectivel y. The increase of bias voltage over 500 V significantly induced selec tive etching of Co and enhanced the substrate temperature higher than 300 degrees C in 10 min, thereby promoting the formation of a dense Ti N film onto it. The prior etching of the surface by Ti ion bombardment with a high bias voltage was very effective in improving the adhesion of the TiN film on Co-WC and therefore reduced plastic deformation an d crack density around the indentation area in a Rockwell C indentatio n test. The impact failure of a TiN coating on Co-WC could be conseque ntly reduced under loads up to 150 N. (C) 1998 Elsevier Science S.A.