Structures and Tribological Properties of TiN/TaN Multilayer Coatings Deposited on Silicon Wafer by Magnetron Sputtering

TiN/TaN multilayer coatings consisting of alternate nanometer-scale TiN and TaN layers were deposited on single crystal Si substrates making use of magnetron sputtering technology. The hardness of the resulting TiN/TaN multiplayer coatings was measured. Their structures were analyzed by means of X-ray diffraction, scanning electron microscopy, and 3-D surface profilometry. The friction and wear behaviors of the TiN/TaN multilayer coatings sliding against AISI1045 steel in a pin-on-disc contact mode under unlubricated conditions were evaluated. The wear mechanisms of the composite coatings were discussed based on the analyses of the worn coating surfaces using a scanning electron microscope equipped with an energy dispersive X-ray analyzer attachment and a 3-D surface profilometer. It was found that the TiN/TaN coatings had good modulation periodicity and sharp interface between the TiN and TaN layers. The TiN layer had a cubic structure, but a hexagonal structure emerged from the cubic TaN layer at a modulation period above 8.5 nm. The microhardness, microstructures, and tribological behaviors of the TiN/TaN coatings were closely related to the modulation period. Namely, the TiN/TaN coating deposited at a modulation period of 8.5 nm had the maximum hardness of 31.5 GPa, which was significantly larger than that of the monophase TiN or TaN coating. This was attributed to the hardening effect and superhardening effect of the composite coatings. Subsequently, the TiN/TaN coatings had larger friction coefficients but much better wear resistance than TiN coating. Moreover, the TiN/TaN coatings were dominated by ploughing, adhesion, and local spalling, as they slid against the steel in unlubricated conditions.