Processing And Properties Of Ultrafine Grained Titanium Prepared By Accumulative Roll Bonding

Titanium and titanium alloys with good biocompatibility and corrosion resistance as biomedical materials are widely used.Ultrafine grains processed by severe plastic deformation has become focus.In this paper,OM,XRD,EBSD,TEM,SEM,tensile test,heat treatment,microhardness,electrochemical corrosion and a series of tests are used on ARB ultrafine-grained titanium,its microstructure,mechanical properties,corrosion resistance and other properties were studied.The results show that: the original state of commercially pure titanium after six circles ARB obviously grained refinement,the band structure transformed into equiaxed grains and grain size refined from original state with 90μm grains to ultrafine crystalline structures.There is an interface between ARB titanium with combine well.With the increasing number of ARB circles,there are more bonding interfaces,and the original bonding interface gradually blurred.But the last rolling binding interface is the most obvious.XRD and EBSD tests showed that after accumulative roll grains are elongated along the rolling direction,compressed,refined,consistent grain orientation.6 circles ARB titanium at different temperatures are heated for half an hour.It occurs recovery when the temperature is below 500℃,there is no significant changes in the organization.When the temperature is 500℃,it begins to recrystallize with clear grain boundaries and equiaxed grains with uniform size.Crystallization temperature occurs in the range of 600℃ to 700℃,equiaxed grains begin to grow into bigger size.After 700 ℃ heat treatment,the grain size increased to 50μm.With the increase of circles,the tensile strength increased from 320 MPa of original state to 750 MPa,elongation decreased from 10% to 3%~4%.The increase of ARB circles contributes to the enhancement of work hardening effects.The tensile strength of 6 circles of ARB titanium is obviously higher than original state commercial pure titanium.ARB results in the pinning and tangling between dislocations within the grains,which contributed to the improvement of the tensile strength.With the increase of ARB circles,the hardness of ARB approaches twice of the matrix’s hardness.With the increase in temperature of the heat treatment temperature,the elongation increased,while tensile strength and hardness decreased.The original state commercial pure titanium possess lower corrosion potential,which resulted in its lower corrosion resistance.The ARB-processed Ti possesses higher corrosion potential compared to the initial state,which illustrated that the corrosion resistance is enhanced after ARB.The corrosion resistance of pure titanium has obviously enhanced after one circle ARB.However,its corrosion resistance starts to decrease as the ARB circles accumulate,but still higher than that of original pure titanium.