Effect Of Doped Y And Cr-Y On The Prepretion And Properties Of Mo-N Films

Molybdenum nitride(Mo-N)film exhibit good stability,high hardness,excel,lent wear resistance and corrosion resistance,which make it play a role of the hard protective coating in the processing of cutting and forming tools.In this thesis,un-doped and metal-doped Mo-N films were successfully fabricated on Si(100)and A 304 stainless steel substrates by magnetron co-sputtering.The structure,micromor-phology,composition,mechanical properties and tribological properties of Mo-N films were studied by X-ray diffiractometry(XRD),scanning electron microscopy(SEM),3D profiler,energy dispersive X-ray spectroscopy(EDX),nanoindentation,friction and wear tester.Firstly,?-Mo2N(111)preferentially grown Mo-N film was successfully prepared on Si(100)substrate by radio freqency(RF)magnetron sputtering.The film has good crystallinity,smooth surface and consists of dense small particles.It is a typical Fee face-centered cubic structure.By changing deposition parameters,the optimum crystalline quality Mo-N film was obtained.The grain size was 25.67 nm,the lattice constant was 0.4172 nm,the hardness was 25.07 GPa,and the friction coefficient and wear rate were 0.370 and 6.17 × 10-7 mm3/Nmm)respectively.Secondly,a series of MoYN films with different Y content were prepared by magnetron co-sputtering.Compared with undoped Mo-N films,the preferred growth orientation of MoYN films changes from ?-Mo2N(111)to ?-Mo2N(200).When the Y content is less than 9.44 at.%,the hardness of MoYN film remains near 24 GPa.However,when the content of Y is 14.81 at.%,the hardness decreases directly to 17 GPa.Y atoms embedded into the grain boundary of Mo-N films can block the grain boundary sliding.Therefore,the hardness of MoYN films with lower Y content does not decrease directly with the introduction of soft metal Y.The minimum average friction coefficient of 0.283 is obtained for the MoYN film with the Y content of 9.44 at.V.which is attributed to the lubrication of soft metal Y.When the Y content is 9.44 at.%,the wear rate of the MoYN film is 5.44 × 10-5 mm3/Nmm,compared with the undoped Mo-N films,the wear rate of MoYN films is two orders of magnitude higher,which is attributed to the formation of low shear strength oxides on the worn surfaces by Y atoms doped into grain boundaries during friction and wearFinally,it is hoped that the mechanical properties and friction and wear prop-erties of Mo-N films can be further improved by co-doping hard metal Cr and soft metal Y.The hardness of MoCrYN film reaches 31 GPa when the content of Cr is 4.44 at.%,which is obviously higher than that of undoped Mo-N film.This is attributed to the solid solution strengthening effect of a small amount of Cr atoms replacing Mo atoms.The average friction coefficient of the MoCrYN film has a minimum value of 0.344 when the content of Cr is 4.44 at.%.which is related to the improvement of the mechanical properties of the MoCrYN film.According to Archard equation,the wear rate of the MoCrYN film is inversely proportional to its hardness.Therefore,the MoCrYN film has the lowest wear rate of 3.7 x 10-7 mm3/Nmm when the content of Cr is 4.44 at.%.It can be seen that the mechan-ical and tribological properties of Cr-Y doped MoCrYN films have been effectively improved.