Effects Of Initial Microstructure On Microstructure And Properties Of Pure Ti Processed By ECAP

Equal Channel Angular Pressing is an effective method to produce ultra-fine grained materials.The hot rolled pure titanium rods?TA1?were used as experimental materials,which were annealed at the temperature of 650?,750?and 950?for 1hour to obtain different initial microstructures of pure Ti.The pure Ti billets with different initial microstructures were processed by multi-pass of ECAP at room temperature.The influence of the initial microstructure on the microstructural evolution and properties of pure Ti processed by ECAP was investigated systematically.The microstructural evolution of pure Ti with different initial microstructures processed by ECAP was analyzed by OM,TEM and EBSD.The results show that the bigger initial grain size is,the more significant grain refinement after 1 pass of ECAP is.After 4 passes of ECAP,the smaller initial grain size is,the more homogenous microstructure and the smaller grain size are.The dislocation slip and twin are the main deformation mechanism for pure Ti during the ECAP at room temperature.The twin statistics show that the number of twin in pure Ti increases sharply after 1 pass of ECAP,and the total number of twin decreases slightly after 4 passes of ECAP.After the ECAP,the number of{101?2}tensile twin increases,but the number of{112?2}and{101?1}compression twin decreases with the annealing temperature increasing.The texture evolution of pure Ti after ECAP was measured by XRD.The texture of the pure Ti annealed at different temperatures is mainly composed of the basal texture and some pyramidal textures,but the strength of texture is different.The texture evolution of pure Ti with different initial microstructures is different during the ECAP.After 4 passes of ECAP,annealing sample B texture and P₁ texture are formed for the pure Ti annealed at 650?and 750?,respectively.After 2 passes of ECAP,C₁ texture is formed for the pure Ti annealed at 950?.The results of tensile and compression at room temperature show that the strength of pure Ti with different initial microstructures increases sharply after 1 pass of ECAP,the strength increases slightly after 2 and 4 passes of ECAP.The strength is directly proportional to the number of twins in the process of ECAP deformation.The more the twins are,the higher the strength is.After 1 pass of ECAP,the strength of pure Ti annealed at 750?is highest and has the largest increase.There is obvious tension-compression asymmetry in ultra-fine grained pure Ti.The tension-compression asymmetry decreases with the grain size decreasing.Anisotropy of uniaxial compressive mechanical behavior is observed in pure Ti processed by ECAP.The specimens under Z and X direction loading display the highest and lowest flow stress values,respectively.