Study On The Structure Design And Tribological Properties Of MoS₂-based Multilayer Films

Two different multilayer films MoS₂/DLC（dia mond-like carbon）and MoS₂/MSN（Mo-S-N composite films）,were prepared on the single crystalline silicon wafers（100）using magnetron sputtering.The influence of mo dulation period（i.e bilayer thickness,Λ）on the microstructure and tribological properties of MoS₂/DLC multilayer fil ms and the influence of modulation ratio,mod ulation period and nitrogen flow rate on the microstructure and tribological properties of MoS₂/MSN multilayer films,were investigated with scanning electron microscope,Raman spectro meter,X-ray diffractometer,trans mission electron microscope and nano-indentation.The lubricating properties of the films we re investigated by the ball-on-disk friction tester in ambient atmosphere or high vacuum environment.Meanwhile,the inherent relationship between the structure,mechanical and the tribological properties of deposited films were studied.The main results of this thesis were obtained as follows:1.A series of MoS₂/diamond-like carbon（DLC）mu ltilayer films with thre e different modulation periods（i.e.Λ of 54 n m,30 nm and 18 nm）were de p o si te d by using a multi-target radio frequency magnetron sputtering of molybdenum disulfide（MoS₂）target and graphite target in argon atmosphere.Results show that the alternative deposition MoS₂/DLC sublayers effectively suppress the growth of columnar structure in sputtered MoS₂ and thus the produced films have compact structure.The hardness of multilayer films increases as the modulation period increases.Compared with pure MoS₂ film,the multilayer film with modulation period of 54 nm shows better load-bearing capacity and elastic recovery capacity,and the corresponding hardness reaches to 7.15 GPa.Meanwhile,TEM analysis of the cross-sectioned multilayer film reveals that the interface between layers is not smooth whereas the periodic structure is dense and well-defined.In addition,the thickness of modulation period is basically consistent with the initial set value.Furthermore,the multilayer film exhibit the lowest friction coefficient（0.09）and wear rate of 1.34×10–7 mm³/（N·m）under a normal load of 5 N in ambient atmosphere（with relative humidity of about 30%）.2.A series of MoS₂/MSN multilayer films were deposited by reactive radio frequency magnetron sputtering of a molybdenum disulfide（MoS₂）target in mixed nitrogen and argon atmosphere,and the influence of modulation ratio（t MSN: t MoS₂ =1:3,1:2,1:1,2:1 and 3:1）,modulation period（Λ: 12¹08 nm）and nitrogen flow rate（0²0 sccm）on the structure,mechanical and tribological properties of multilayer films were investigated.Results show that alternate deposition MoS₂/MSN sublayers effectively suppress the growth of columnar structure in sputtered films and thus produce an amorphous structure.（1）The hardness of multilayer film with mixed nitrogen and argon flow ratio of 40/4 sccm rises basically from 1.63 to 2.44 GPa as modulation ratio of MSN and MoS₂ sublayers increases from 1:3 to 3:1.（2）Furthermore,when the suitable modulation ratio is set as 1:1 at the mixed nitrogen and argon flow ratio of 40/4 sccm,and consider the demand of friction（the following all experiments choose the ratio）,the hardness of multilayer film increases as the modulation periods increases.（3）The modulation period is set as 30 nm,the hardness increases firstly from 2.26 to 10.47 GPa as the nitrogen flow rate increases to 10 sccm and then turned downwards,contributing the maximum hardness of 10.47 GPa at nitrogen flow rate of 10 sccm.By contrast,while the modulation ratio is set as 1:1 with the mixed nitrogen and argon flow ratio of 40/6 sccm,the film hardness increases firstly from 1.33 to 4.13 GPa as the modulation period increases from 12 to 30 nm,and then decreases continuously to 1.06 GPa with further increasing of modulation period up to 108 nm,which has the highest elastic recovery rate of 41.0% at the modulation period of 30 nm.3.The high vacuum tribological tests performed on a ball-on-disk tribometer under a 3 N normal load indicate that the multilayer films have low friction coefficient（less than 0.035）and wear rate（less than 1.0×10-6 mm³/（N·m））at the modulation period of 18 to 54 nm and nitrogen flow rate of 4 to 10 sccm with modulation ratio of 1:1.More interestingly,the super-low friction coefficient（0.004⁰.01）and low wear rate（4.68×10-7 mm³/（N·m））at long sliding cycle of 1.8×105 revolutions can be obtained in a suitable nitrogen flow rate（4¹0 sccm）and modulation period（30 nm）with modulation ratio of 1:1.Furthermore,the ultra-low friction behavior maintains 8.0×104 revolutions under high vacuum conditions.