Influence of Mo content on the properties of multilayer nanostructured coatings based on the (Mo,Cr,Al)N system.

Abstract

The study is focused on the comparison of two coatings with the identical thickness, structure, and the content of aluminum (Al) (10 at %), but different ratios of chromium (Cr) and molybdenum (Mo) content in the wear-resistant layer of (Mo,Cr,Al)N: Cr/Mo – 70/20 and 45/45 at%. The tribological properties of the coatings within a range of the temperatures of 500–900 °C and the wear resistance of carbide tools with the coatings under study during the turning of 1045 steel were considered. The study was also focused on the wear patterns on the coatings and diffusion and oxidation processes during the cutting. While there is a rather active formation of an aluminum oxide layer on the free surface of the coating, this layer is not able to have any noticeable effect on the cutting conditions, since it is not directly involved in the cutting process. The contact pads of the tool bear no such layer or extremely small amount of this layer (at an adherent boundary). At the same time, the presence of chromium and molybdenum oxides are detected in the contact areas, and therefore, these oxides can affect the cutting process. The coating with the Mo content of 45 at% ensured both the minimum of the adhesion component of the coefficient of friction (COF) during the tribological tests at high temperatures (800 °C and higher) and the maximum wear resistance during the turning of steel.