The Effect Of Design Of Multilayer Structure On The Mechanical Properties Of Carbon-based Films

(1) Alternate hard and soft diamond-like carbon （DLC） multilayer coatings with differentmodulus and stress ratio between adjacent sub-layers were prepared using magnetron sputtering bycontrolling deposition bias. The effect of modulus and stress ratio between adjacent sub-layers on thehardness, toughness and tribological properties under dry and water-lubricated sliding conditions werestudied systematically. Multilayer strengthening effect did not appear in multilayer DLC coating. Thetoughness of multilayer DLC coatings deposited at-120/-160V has the highest value and was double of thatof monolayer DLC coatings. Contrary to fracture toughness, the toughness of coatings was in inverseproportion to modulus and stressratio because multilayer with low modulus ratio decreased the stressconcentration in harder sub-layer and avoided the crack initiation. Under both dry and water-lubricatedsliding conditions, wear rate of multilayer DLC coatings was half of that of monolayer coatings. Formultilayer coatings, high toughness was consistent with high wear resistance, demonstrating that toughnessof coatings consisting both crack penetration and crack initiation was more suitable for evaluating coatingmechanical properties than fracture toughness consisting only crack penetration.（2）In this study, nc-TiC/a-C:H nanocomposite films were prepared by filtered cathodic arctechnique. The influence of C₂H₂/Ar flow ratio on the composition, structure and mechanical properties offilms was investigated by using XPS, XRD, Raman spectroscopy, nanoindentation, ball-on-disc tribometry,and so on. The films were consisted of two phases: TiC crystallites embedded in the amorphous matrix ofa-C:H phase. As the flow ratio of C₂H₂/Ar increased, the C content improved and the crystallite size of TiCdecreased. By selecting the proper value for the C₂H₂/Ar flow ratio of12, the nc-TiC/a-C:H films had a pronounced hardness maximum of30GPa. No obvious correlation was found between hardness andtribological performance, which was only controlled by the sp2content of the films. Higher sp2contentand the presence of TiC nanocrystallites promote formation of graphite-like transfer layer during the sliding.The adhesion strength showed quite similar trends, which was enhanced with increasing the C₂H₂/Ar flowratio.（3） In this study, Alternate hard and soft nc-TiC/a-C:H multilayer films were prepared by filteredcathodic arc technique. The effect of modulation period and the match of the sub-layer s on the structureand mechanical properties were studied systematically. When fixed the match of the sub-layer and changedthe modulation period, the internal stress of the multilayer films had the lowest value under the sub-layer of40nm. The trend of the wear rate of the films first decreased and then increased with raising the thicknessof sub-layer. As the thickness of40nm, the wear rate had the minimum value. Selecting the sub-layerthickness of20,40,60nm, which had the lower wear rate, and changing the match of hard and softsub-layer, the films always had the lowest wear rate at the samples of1-10/1-12.