Performance evaluation of TiN coated high-speed steel drill bits

Usage of stainless steel materials has increased continuously in various industrial applications. However the machinability of these materials is difficult. The stainless steels in general are considered to be difficult to machine materials. This is mainly due to the high plasticity and tendency to work-harden of the stainless steel, which usually results in severe cutting conditions. Additionally, stainless steels have much lower thermal conductivity as compared to structural carbon steels; this inflicts high thermal impact within the chip-tool contact zone, which significantly increases the cutting tool wear rate. High speed steels (HSS) tools are commonly used for drilling/tapping/turning operations. The surface is either untreated or coated with physical vapor deposition (PVD) coatings. In most cases TiN, TiCN or TiAlN coatings are used. The adhesion is of vital importance for the performance of tools coated with titanium nitride. Proper surface treatments (in situ and ex-situ) are required to achieve highly adherent coatings.\ud We have deposited TiN coatings on high-speed steel drill bits and other substrates using a four-cathode reactive DC magnetron sputtering system. Various treatments have been given to the substrates for improved adhesion of the coating. The process parameters have been optimized to achieve thick and highly adherent good quality TiN coatings. These coatings have been characterized using a variety of techniques. The performance of the coated drill bits is evaluated by drilling a 13mm thick 304 stainless steel sheet under wet conditions. The results are compared with the standard commercially available TiN coatings.\u