Study On The Effect Of Mechanical Hammering And High Temperature Annealing On The Surface Nanocrystallization Mechanism And Properties Of ? Titanium Alloy

?-titanium alloy has become a research hotspot in the field of biomedical materials due to its good biocompatibility,high specific strength and low elastic modulus.However,in the process of human service,there are still problems of poor fatigue strength,insufficient wear resistance and corrosion resistance,which seriously reduces the service life.Therefore,surface modification of?-titanium alloy is the key to expanding its use range.This thesis takes the metastable?-titanium alloy Ti-15Mo(TB11)as the research object,and uses mechanical hammering and high-temperature annealing to nanometer the surface of TB11 alloy.Using XRD,OM,SEM and other analytical testing methods to investigate the effects of different hammering time and annealing temperature on the surface structure and microstructure of TB11 alloy,discuss the formation mechanism of TB11 alloy surface nanocrystallization;establish a numerical model of fatigue life of mechanical hammering TB11 alloy;Through nanoindentation,friction and wear and electrochemical experiments to characterize the microhardness,wear resistance and corrosion resistance of the TB11 alloy surface after nanometering,and reveal its change mechanism.The surface nanometer of TB11 alloy was realized by mechanical hammering and high temperature annealing.The results show that the surface grain size of TB11alloy decreases gradually with the increase of hammering time,and fi rst decreases and then becomes larger with the increase of annealing temperature.Among them,the size of the grains of hammering 30min+650?is the smallest,which is 14.64nm;plasticity The thickness of the deformed layer increases first and then stabilizes with the increase of hammering time,and the maximum value of the deformed layer is350?m;The surface nanocrystallization of TB11 alloy is mainly attributed to the twin deformation and dislocation slip inside the grains.The sample was measured by the HB-1000A type microhardness tester.Based on ABAQUS and Fe-safe software,a finite element analysis model for fatigue life of TB11 alloy was established.The CMT-1 type testing machine was used to test the friction and wear properties of TB11 alloy,and the pin-disk wear model was used to characterize the specific wear conditions.The results show that the microhardness of TB11 alloy increases significantly after hammering treatment,and it changes gradually with depth.As the annealing temperature increases,the hardness of the material surface first becomes larger and then becomes smaller.Compared with the original sample,the hardness of the outermost layer was increased by about 42.5%by hammering for 40 minutes.When the grain size is not less than 30.84nm,the hardness and grain size conform to the Hall-Petch formula;within a certain range,as the number of hammering increases,the fatigue strength of TB11 alloy will gradually increase.When the number of hammering increases from 1 to 3 times,the fatigue life of the impact point is increased by about 42%;the hammering and annealing treatment significantly enhance the wear resistance of TB11 alloy,and the wear resistance of TB11 alloy annealed at 650?for 30min+650?the best.Relative wear resistance increased by 2.33 times.Especially under high load,the abrasion resistance is particularly enhanced.The increase in wear resistance of TB11 alloy surface after nano-treatment is mainly due to the refinement of grain size and the introduction of residual stress.When the grain size is reduced to 32.21nm,the wear depth is reduced by about 29%compared with the original grain.The electrochemical workstation PARSAT4000 was used to investigate the corrosion behavior of TB11 alloy in 0.9%Na Cl solution and 0.2%Na F solution.The results show that hammering and annealing treatment can significantly improve the corrosion resistance of TB11 alloy.The corrosion resistance of hammering for30min+650?is the best,the self-corrosion potential is positively moved by 0.29V,and the self-corrosion current density is reduced by 188.75n A/cm~2.The improvement of corrosion resistance is mainly attributed to the increase of surface reactivity of TB11 alloy after nanometering,and the surface is easy to quickly form a unifor m and dense passivation layer.