Self-lubricating CrAlN/VN multilayer coatings at room temperature

Vanadium nitride (VN) is easily oxidized to form vanadium oxides and becomes lubricious under stress. CrAlN is hard thus CrAlN/VN multilayer coatings render both hardness and lubricious properties attractive in dry machining of soft metals. This study investigates the effect of multi-layering on the coating's mechanical and tribological properties at room temperature. The CrAlN/VN multilayer coatings are deposited on cemented tungsten carbide and Si wafer (1 0 0) substrates in an in-line magnetron sputtering system. A period contains one layer of CrAlN plus one adjacent layer of VN. The period thickness varies roughly from 3 nm to 30 nm; the total number of the periods varies from 30 to 300. X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and electron probe micro-analyzer are employed to characterize the microstructures and chemistry. Nanoindentation and ball-on-disk wear test are used in mechanical and tribological studies. The CrAlN/VN multilayer coatings have good lubricant property with lowest coefficient of friction of 0.26. At the period thickness of 20 nm, the multilayer coatings obtained the best mechanical properties (hardness of 32.4 GPa, elastic modulus of 375 GPa, minimum wear rate of 1.1 × 10−7 mm3/Nm).