Investigation Of Tribological Behaviors Of AlMgB₁₄-TiB₂ Coatings Under MoDTC Lubrication

To slow down the wear of mechanical components and reduce the energy loss caused by friction,anti-wear coatings and fully-formulated lubricants are often applied to the surface mechanical components.Boride anti-wear coatings,especially the AlMgB14-TiB2 coatings,have shown excellent mechanical properties,and these coatings exhibit good tribological properties under dry friction and oil lubrication.It is believed that boride coatings have great application and research value in production.Under boundary lubrication,AlMgB14-TiB2 coatings have shown synergistic interaction with some lubricant additives.This suggests that these coatings can improve the performance of lubricant additives and tribological properties of tribopairs under boundary lubrication.Current developed lubricant additives are mainly designed for steel tribopairs.Interactions between these lubricant additives with non-ferrous coatings are not clear.Even some additives will lead to the wear acceleration of coatings and tribological performance deterioration of tribopairs.To improve the tribological properties of antiwear coatings under oil lubrication,these coatings are often modified to enhance the interaction between coatings and additives.In this work,we conducted a systematic study on the chemical composition and mechanical properties of nitrogen-incorporated AlMgB14-TiB2 coatings deposited by magnetron sputtering technology.Tribological propertied of nitrogen-incorporated AlMgB14-TiB2 coatings and interaction between molybdenum dialkyl-dithiocarbamate(MoDTC)with these coatings were studied.Tribological behaviors of tribopairs were examined by unidirectional ball-on-disk tribological tests.The coatings and wear tracks were characterized by Scanning Electron Microscopy(SEM),Energy Dispersive X-ray Spectroscopy(EDS),Raman Spectroscopy,X-ray Photoelectron Spectroscopy(XPS),X-Ray Diffraction(XRD)and Nanomechanical test system.The results are as follows:(1)AlMgB14-TiB2 coating deposited by DC magnetron sputtering has excellent mechanical properties and exhibits the hardness of 30GPa.Nitrogen incorporation of coating was achieved by mixing N2 and Ar during deposition.Nitrogen tends to bond with boron and titanium,then suppressed formation of B12 and TiB2 hard phases.Thus,nitrogen incorporation causes the deterioration of coatings’ mechanical properties.(2)Under boundary lubrication,MoDTC has synergistic interaction with AMTB-N Coatings.Friction coefficients of tribopairs dropped rapidly during running-in period and maintained a steady level.For AMTB-0N,AMTB-20N and AMTB-30N,steady friction coefficients ranged from 0.06 to 0.07.The friction coefficient of AMTB-10N gradually reached a steady value of～0.02.Formation of MoDTC-derived MoS2 tribofilms were found on coatings after tribological tests and chemical composition characterization.There is a correlation between mechanical properties of coatings and morphology of tribofilms.Better mechanical properties of coatings can cause higher tribofilm coverage.Nitrogen incorporation of AlMgB14-TiB2 coatings can induce the formation of TiO2-x,which containing oxygen vacancies Vo and Ti3+.Ti3+on the surface can suppress formation of MoO3/FeMoO4 in MoDTC tribofilms and improve amount of MoS2 in tribofilms.Higher coverage and more MoS2 in MoDTC tribofilms will induce lower friction coefficient of tribopairs.(3)By depositing active films with TiO2-x on hard coatings,we can obtain coatings have excellent mechanical properties and synergy with MoDTC.Under lubrication of MoDTC,these coatings can reduce steady friction coefficient of tribopairs.