Study On Plastic Deformation Behavior And Mechanical Properties Of Pure Titanium

In this paper,the microstructures and mechanical properties of pure titanium(TA2)after different rolling conditions and subsequent recrystallization annealing were studied.The mechanical properties were measured by universal tensile machine and microhardness tester.The microstructure was characterized by metallographic microscope(OM),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).Firstly,the evolution of mechanical properties of pure titanium after large strain cold rolling at room temperature and subsequent recrystallization annealing with different parameters were investigated.The results show that the strength of pure titanium is remarkably improved after large-strain cold rolling.After recrystallization annealing,the strength of pure titanium decreases while its plasticity recovers,and a heterogeneous lamella structure was obtained through annealing at 450℃ for 0.5 h,which improves the strain hardening rate during the tensile process.The heterogeneous lamella structure can increase the strain hardening rate by back stress strengthening,and this ability is related to the ratio of recrystallized grain.Secondly,the mechanical properties and microstructural evolution of pure titanium with different grain sizes rolled in liquid nitrogen with small deformation were studied.The results show that liquid nitrogen temperature rolling(LNR)with small deformation stimulates highdensity twinning and significantly improves the strength of pure Ti.The {11(?)2} compression twins and {10(?)2} tension twins are the two main types of twinning motivated during LNR.The {11(?)2} compression twinning are mainly primary twinning,while {10(?)2} tension twinning are mostly secondary twinning with {11(?)2} compression twinned as the matrix.The proportion of twin boundaries tends to be equal with the increase of strain,but the proportion of {11(?)2} compressed twin area is always much higher than that of {10(?)2}} tension twin.Finally,the discontinuous yield phenomena of pure titanium is investigated studied.The results show that the yield drop of pure titanium during tensile test is due to the fact that the critical shear stress(CRSS)required to start < c+a> dislocation is larger than the stress required to slip.With the < c+a> dislocations continuously stimulating and entangling at the yield platform stage,the mechanical curves of the tensile specimens enter the strengthening stage again because of the secondary hardening effect of the remarkable work hardening ability.