| Titanium nitride (TiN) coatings have high hardness, good wear and corrosionresistance, and have been used as wear resistant coatings for cutting tools and dies. Inrecent years, they have been used in medical fileds like artificial internal organs andoptical fields like solar films. However, along with the gradual developments ofindustries and technologies, there are more and more precise parts with higherrequirements on good surface properties of TiN coatings. Moreover, it is impossiblefor TiN coatings to be used on machine parts in fields like special drilling enginnering,automobile industry, or other critical mechanical engineering industries. Therefore,besides good wear resistance, lower friction coefficient and better anti-frictionproperty are supposed to be essential properties for TiN coatings in some specialmechanical industries and machining environments.In this paper, low-friction and hard TiN-W/Mo(Sx) coatings were prepared bycombining treatments of Ion plating, Metal ion implantations, Magnetron sputteringdoping (MSD), and Low temperature ion sulfuration (LTIS), with the metal W andMo as the mainline. The tribological properties of coatings were carried out on aMS-T3000ball-on-disc friction and wear tester. The surface morphology before andafter wear, microstructures, elment valence, and hardness were investigated by thethree-dimension optical profilometer, scanning electron microscope (SEM), X-raydiffraction (XRD), Scanning Auger microprobe (SAM), X-ray photoelectronspectroscope (XPS), and Nano-hardness tester. Also, the anti-friction mechanism ofTiN-W/Mo(Sx) coatings was proposed.The results demonstrated that W or Mo implanted layers with thickness of about100~200nm could be prepared on Ion plating TiN coatings by Metal Vapor VacuumArc (MEVVA) source. New phase of Ti2N appeared on surfaces of TiN coatings afterion implantations. Under lubrications of W oxides or Mo oxides, and their effectiveprolonging of the lubrication time of Ti oxides, W-implanted and Mo-implanted TiNcoatings could obtain much better low-friction properties with higher contents of Moions and W ions, better tribological properties and more obvious sputtering effects atimplantation doses of9E17for W ions and1E18for Mo ions. After post-treatmentsof LTIS, obvious sputtering effects were shown on W-implanted and Mo-implantedTiN coatings, with evident decreasing of implantation depth and contents of W andMo ions and significant decreasing of coating hardness. A metal sulfide layer of about20~50nm were formed on W-implanted and Mo-implanted TiN coatings, whichcould further reduce the friction coefficients of coatings only for a short period at thebegnnning stages of wear. By combining the treatments of MSD and LTIS,TiN-W/Mo(Sx) coatings were prepared on316L stainless steel substrates, with thethickness of about2.5μm. It was found that depostion rates and surface hardness ofcoatings increased along with the rising of target current of W or Mo. The phases ofTiN-WSxand TiN-MoSxcoatings mainly included TiN, W2N, W, WS2and TiN,Mo2N, Mo, MoS2, respectively. Abrasive wear and adhesive wear of coatings weresignificantly reduced, and the low-friction and anti-wear properties were improvedfurther along with higher contents of W or Mo in coatings. The anti-friction mechanism of TiN-W/Mo(Sx) coatings included four factors, which were lubricationof Ti oxides, lubrication of WSx/MoSx, lubrication of W oxides or Mo oxides, andsuperposition effects of multi-lubricants. On one hand, WSxand MoSxhad the layeredstructures and excellent lubricantion effects, which played the most important roles inthe anti-friction process of TiN-W/Mo(Sx) coatings. On the other hand, the reciprocaltransformation among W-WSx-WOxor Mo-MoSx-MoOxand the effective extendingof lubrication time of metal oxides, especially for Ti oxides, made the coatings be ableto maintain good low-friction properties in a much longer time. |
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