Study On Tensile Mechanical Properties And Microstructure Of Titanium Foils

Titanium foil has been widely applied in the fields such as electronics and medical devices.In this paper,a post-doctoral project,the mechanical properties and microstructure of fully recrystallized commercial pure titanium foils with a thickness of 5²00?m are systematically studied by using room temperature tension,metallographic microscope,X-ray diffraction?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?,and the size effect of titanium foils were discussed.The main conclusions are as follows:?1?The mechanical properties of titanium foil are affected by the size effect.The yield strength and the tensile strength of Ti foils are constant when the thickness is above 50?m.The strength drops with decreasing thickness when the thickness ranges from 50?m to30?m,and the strength increases with decreasing thickness when the thickness is lower than 30?m.As a whole,the titanium foils with the thickness greater than 30?m are higher in both tensile and yield strength than that of the titanium foils with the thickness less than 30?m.In addition,the elongation decreases with the decrease of the thickness.?2?When the thickness is greater than 20?m,the fracture mode of titanium foils is shear fracture,and the angle between the shear direction and the tensile direction is between 50°and 60°,and a large number of dimples can be observed on the fracture.When the thickness is less than 20?m,the angle between the fracture surface and the tensile direction of titanium foil samples is close to 90°,which is a positive fracture surface.The dimple structure is not found on the fracture surface,but a small amount of tearing edges and slip marks can be observed.It can be seen that the fracture mode of titanium foil changes from plastic fracture to brittle fracture.?3?According to the tensile experimental datas of titanium foil with different thicknesses,two different types of constitutive equations were constructed based on the Hall-Petch relationship and the surface layer model,taking into account factors such as the grain size of the material and the fraction of the thickness to grain size.The new constitutive model can well match the experimental results.?4?The plastic deformation mechanism of Ti foils includes dislocation slip,deformation twins and the phase transition from HCP-Ti to FCC-Ti.The density of the deformation twin decreases with the decrease of the thickness of Ti foils.The elongated needle-shaped FCC-Ti phase formed during the stretching process is mainly distributed near the fracture surface and has a width of 15 nm to 100 nm.The orientation relationship between HCP-Ti and FCC-Ti phases is:<0001>_HCP//<001>_FCC,{2?110}_HCP//{???10}_FCCCC and{01???0}HCP//{110}FCC.The orientation relationship between the two phases can be converted by the transformation matrix B.