Preparation Of Ag/TiO₂ Gradient Composite Film On Titanium TA2 For Ocean Engineering And Research On Its Friction And Wear Properties

Ti and Ti Alloys are one of the prime ship structural materials due to its low density,high specific strength,excellent corrosion resistance,non-magnetism and good workability.However,its abrasive resistance is poor and it is easily scratched and adhered,which imposes restrictions on its application.As the requirement of marine Ti and its alloys are gradually increased,single modification can not meet the requirement anymore and the composite film which contains nano-structures has been the prevailing development tendency for the surface modification of titanium.Surface mechanical attrition treatment?SMAT?,Ti-Ag co-sputtering,and thermal oxidation were used in this thesis to prepare the Ag/TiO₂ gradient composite film on TA2.The interface structure of the film as well as its friction and wear behavior was also investigated.At first,nanocrystalline Ti layerwere prepared on the surface of TA2 via SMAT,and the average grain size of the ultra-fine grains was 122.44 nm.The grain refinement was achieved through the sliding of dislocations and the intersection of twins,and the grain size increased gradually from the treated surface to the matrix of Ti.The SMAT TA2 samples were annealed in order to investigate the thermal stability of the surface nanocrystalline Ti.The results suggested that the SMAT TA2 samples had good thermal stability at or below 450?,and the grain growth of the SMAT TA2 sample was obvious when it annealed at or higher than500?.The uniform and compact Ti-Ag films were deposited on coarse-grain TA2 and SMAT TA2 through co-sputtering.The thickness of the film was 494.37 nm and the particle size was121.93 nm when the sputtering time was 20 min.When the sputtering time was 60 min the thickness of the film reached 494.37 nm while the particle size was 121.93 nm.Ag particles with the mass content of⁵wt%in the film were uniformly distributed with slight agglomeration somewhere in the filmThe sputtering samples were oxidized at 450?in a tube furnace for an hour,after which the color of the samples turned into blue-violet,and the films were also uniform and compact.The micromorphology of the film was also changed as compared with that of the sputtering samples.The thickness of the 20 min-sputtering film was 583.46 nm while the oxide thickness was 110.58 nm.The thichness of the 60 min-sputtering film was 1236.54 nm nm whle the oxide thickness was 173.08 nm.The product of the thermal oxidation was rutile-TiO₂.After thermal oxidation Ag particles were still uniformly distributed in the film,and the size as well as the distribution of the agglomerated particles was not uniform due to the different growth rate of Ag particles on the different crystal faces of TiO₂ film.Friction and wear tests were conducted in all samples.It was found that the wear mechanism was abrasive wear,and the wear volume increased with the increase of the load.The abrasive resistance of SMAT TA2 samples was better than that of coarse-grained TA2samples under the same load.In addition,the wear resistance of SMAT TA2-based film samples was also better than that of coarse-grain TA2-based film samples.The wear resistance increased with the increasing of film.The gradient composite film significantly improved the wear resistance of TA2,and the effect was more obvious with the increasing of load.The gradient composite film showed excellent bonding with and its substrate.The rutile TiO₂ on Ti surface increased the hardness of the sample,while the soft Ag particles reduced the brittleness and increase the lubricity of the film simultaneously,which greatly improved the wear resistance of film samples.