Mechanical and Tribological Properties of NbTi-NX and NbTi-N12-CH Coatings Prepared Using Radio Frequency Magnetron Sputtering and Their Application for Micro-drills

Abstract

In this study, NbTi-NX and NbTi-N12-CH coatings were prepared using radio frequency magnetron sputtering on high-speed steel substrates, where X represents the flow rate of nitrogen and CH represents a coating containing carbon and hydrogen integrated with acetylene. The crystalline phases were characterized using x-ray diffraction, and the surface and cross-sectional structures were analyzed using scanning electron microscopy. The x-ray diffractometry results revealed that except for the NbTi-N8 and NbTi-N12-CH coatings, all other coatings exhibited a crystalline phase. Five peaks were observed for the NbTi-N12 coating as follows: TiN (111), (200), and (222) and Nb2N (110) and (112). Thus, this structure had the most diversified orientations. The x-ray photoelectron spectroscopy results revealed that only the NbTi-N4 coating had pure niobium- and titanium-binding energies. For the other coatings, some Nb-N and Ti-N bonds were oxidized to form Nb-ON and Ti-ON, respectively. Regarding the mechanical properties, the NbTi-N12 coating had the highest hardness value (26.6 GPa). A wear test was conducted with a load of 5 N, and the NbTi-N12 coating exhibited the lowest wear rate in the NbTi-NX coating series. Conversely, the NbTi-N12-CH coating had the best tribological properties, such as the lowest friction coefficient (0.137), wear depth (0.203 μm), and wear rate (0.85 × 10−6 mm3/Nm). For the substrate wear performance, the wear depth and wear rate were approximately 13.7 and 13.2 times higher than those of the substrate with the NbTi-N12-CH coating, respectively. We applied the NbTi-N12-CH coating to a micro-drill and tested it by high-speed drilling 2000, 4000, and 6000 holes. The results revealed that when this coating was applied to micro-drills, their drill life could be increased to 4000 holes, which is twice that of an uncoated micro-drill.