Oxidation behavior of magnetron sputtered Mo2N/AlN multilayer coatings during heat treatment

The Mo2N/AlN multilayer coatings with AlN layer thickness in the range of 0.5 nm to 3.7 nm were deposited by dc magnetron sputtering. The Mo2N/AlN multilayer coatings exhibited columnar growth structure. As the AlN layers’ thickness exceeds 1.2 nm, AlN layers changed from fcc structure to amorphous structure, which breaks off the crystallization integrity of multilayer coatings. The coatings oxidized at 400 °C, 550 °C, 700 °C in air for 1 h were investigated by X-ray diffractions (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM). It was found that with the increase of AlN layer thickness, the oxidation resistance of Mo2N/AlN multilayer coatings was improved by reducing the density of columnar grain boundaries and forming dense Al2O3 oxide layer on the surface. The addition of AlN to Mo2N coatings also leads to the lower coefficient of friction (0.36–0.42) of Mo2N/AlN multilayer coatings than that (0.62) of Mo2N coatings.