Study On The Fabrication,Microstructure And Properties Of Fine-grained Commercial Pure Titanium TA2 By FSP

Due to its low density,high specific strength,good corrosion resistance and other advantages,commercial pure titanium TA2 was widely used in Marine engineering equipment manufacturing industry.However,because of existing TiO2 oxide film on the surface which is easy peeling,low plastic shear resistance and work hardening properties,which affect its wear resistance and Cold workability,thus seriously limits the application of titanium.In this paper,Friction Stir Processing(FSP)was used to prepare fine crystal structure material of commercial pure titanium TA2,and the change of the different parameters(Processing speed and mixing head rotation speed)of the microstructure and performance has carried on the research,the results are shown below:(1)FSP technology is an effective way of fine grains.The average grain size of the RD-ND section presents gradient distribution that increase gradually from surface to interior.The uniform surface annular texture can be obtained and surface formability is best when the FSP process parameters are the following:the tilt angle is 2°,a penetration depth of stir should of 1 mm,the number of FSP passes is 1,a rotation speed of 180 r/min,the processing speed is 25 mm/min,and under nitrogen protection.(2)After FSP treatment,the surface texture of the TA2 sample was changed from a typical bimodal basal texture to basal texture.The grain orientation of FSPed sample also has changed obviously from from surface to interior compared with the original TA2 sample,and the intensity of the texture also changed.The degree of recrystallization present a gradually decreasing from surface to interior.(3)The hardness and wear resistance of the FSPed samples have obvious improvement compare to the original sample.when the parameters of the rotation speed and transverse speed were 180r/min,25mm/min,respectively,the hardness and wear quality of FSPed sample increased by 20.2% and decreased by 60% respectively compared with the original sample.The wear mechanism of industrial pure titanium TA2 is: severe grinding particle attrition,oxidative wear and adhesive wear plus slight wear and fatigue spalling wear.After friction stir processing,the wear mechanism changed,the main wear mechanisms of FSPed sample is: grinding particle attrition,oxidative wear and mild adhesive wear.(4)The fine-grain TA2 samples were annealed at 400 ? ~600 ?.The results show that grain size,the surface hardness and uniformity has no obvious change when the annealing temperature at 450? or below,so the structure has good thermal stability;when the annealing temperature to 500?,grain size increases and hardness decrease compare to the unannealed sample,so the organization structure has poor thermal stability.When the annealing temperature is 600?,the grain size increases obviously,and the microstructure and hardness are similar to that of the original sample.Therefore,the thermal stability of the structure is poor when the temperature is above 500 ?.