Increase of coating thickness on sharp edges, deposited by cathodic arc evaporation

Abstract

When depositing a coating on a complex-shaped tool, using a PVD processes with a high ionization rate such as cathodic arc evaporation, the electric field lines concentrate on sharp edges. Therefore the deposition rate at the edges increases. In this paper we evaluated that effect in a standard industrial batch for TiAlN deposition. Two types of substrates (standard drills and cylindrical rods) of various diameters (from ∅3 to ∅8 mm) were mounted in different configurations by varying the vertical distance to the top plate of the carousel and the horizontal distance between the substrates. Coating thickness was evaluated on cross-sections in two directions: perpendicularly (from the flank face towards the minor cutting edge) and vertically (along the tool axis towards the tool top). The coating thickness increased in both directions, generally following a sigmoid curve with a constant relative thickness increase for a factor of 1.5 just at the edge of the flank face. The two mounting parameters contributed 1–2 μm of additional coating thickness if the tool was mounted with more empty space in the neighborhood. The opposite effect was found when increasing the tool diameter. At a corner where two edges meet, the effects for both edges multiply, yielding up to 11 μm despite the targeted thickness was only 3 μm.