Evaluation of Arc Evaporated Coatings on Rounded Surfaces and Sharp Edges

Abstract

This paper presents measurements and cutting tests related to coating features on sharp cutting edges and rounded objects. One typical feature of plasma based deposition processes is the formation of a sheath region around the object to be coated. The formation of the sheath has some implications on the coating of three dimensional objects, since rounded surfaces and edges are subjected to different ion flux density as compared to a flat surface. Solid carbide drills of different diameters were coated with a TiAlCrSiN coating by cathodic arc evaporation. It is noted the deposition rate increases with decreasing drill diameter, and the fraction of elements with high expected mean ionization charge state is higher for a small as compared to a large diameter drill. The observations are explained by Coulomb attraction of ions from the plasma in combination with the sheath to tool radius ratio in combination with resputtering and scattering in the gas/plasma phase. Solid carbide end mills were coated with TiAlN at three different substrate biases; -10, - 40, and - 80 V. It is observed that the coating stresses increase drastically with increasing bias, and the corners of the tools have different stress levels than the flatter areas. In addition, the fraction of Ti in the coating around the corners is increased significantly when the bias increases. The end mills were tested in a machining test, and the best performer was the variant deposited at - 40 V.