Improving mechanical properties of a-CNx films by Ti–TiN/CNx gradient multilayer

Amorphous carbon nitride (a-CNx) films with functional gradient Ti–TiN/CNx underlayer were deposited by direct current magnetron sputtering. Microstructure and composition of the films were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, atomic force microscope (AFM) and transmission electron microscopy (TEM). Mechanical and tribological properties were investigated by nanoindenter, scratch and ball-on-disk tribometer. The a-CNx-based films suffer a graphitization process with the increasing deposition temperature, thus the hardness and elastic modulus decrease. With the design of the Ti–TiN/CNx gradient underlayers, some important advantages of relatively thick CNx films can be achieved, such as increased hardness, improved adhesion strength, and the wear resistance of the a-CNx-based films can be also improved significantly.