Taguchi Methods to Optimize TiN Coating Surface Roughness

Cathodic Arc Physical Vapor deposition (CAPVD) uses a high current, low and negative voltage arc to vaporize a cathodic electrode (cathodic arc) and deposit the vaporized material on a substrate. The vaporized material is ionized in a vacuum chamber and the substrates are usually biased so as to accelerate the ions to the substrate surface. CAPVD provides a very dense film with excellent adhesion to the substrates. Therefore, this technique is mainly used to deposit on cutting tools such as end mills, drills, inserts, plastics and metal molds and high wear resistance tribology components. However, this coating technique will produce unwanted micro particles (droplets) which usually are the target materials that cannot be reacted in coating process. These particles will affect the coating roughness and the surface morphology. To optimize this condition, Taguchi method is introduced to obtain the best experimental parameter settings. In this study, Atomic Force Microscope (AFM) is used to analyze the roughness of the coating for the following factors: bias voltage, arc current, nitrogen pressure and coating thickness. (Substrate: ASSAB 88 prehardened mold steel.