Preparation And Mechanical Property Study Of Gradient Structure Titanium Plate

Titanium with good corrosion resistance,high specific strength and low density is widely used in aerospace,automotive and other engineering.With the rapid development of science and technology,the demand for titanium to manufacture parts is increasing,and the performance requirements for titanium are also increasing.That is,while maintaining sufficient plasticity,the strength needs to be greatly improved.In this paper,pure titanium foils with different original grain sizes were laminated.Layered gradient structure pure titanium plate with gradual increase of grain size from edge to core was prepared by hot pressing sintering process,and layered pure titanium plate with uniform thickness of single grain size was prepared.The microstructure of the prepared titanium plate was characterized by metallographic microscope and electron backscatter diffraction（EBSD）,and its mechanical properties were tested.The in-situ tensile and EBSD techniques based on SEM were used to study the deformation and fracture failure behavior of pure titanium plate with layered gradient structure,and the strengthening mechanism and fracture mechanism were revealed.The grain size of the gradient material sintered at 720°C,45 MPa for 2 h shows a gradient change from the edge to the core,that is,the grain size in the edge region is the smallest,followed by the middle layer and the core grain is the largest.The obtained three kinds of titanium plates have strong texture,which is bimodal distribution along ND direction and TD direction.The yield strength of the layered gradient structure titanium plate was increased by 35.9% and 41.3% compared with that of the pure coarse-grained layered titanium plate and the fine-grained layered titanium plate,respectively,and the tensile strength was increased by 17.3% and 16.8%,respectively.However,the fracture elongation was close to that of the pure fine-grained layered titanium plate.The layered gradient structure titanium plate maintained the fracture elongation of the fine-grained layered titanium plate,and at the same time obtained the strength higher than that of the finegrained layered titanium plate and the coarse-grained layered titanium plate.Based on the in-situ tensile and EBSD analysis of SEM,it is found that the cracks preferentially initiate in the fine crystal layer during the tensile deformation of the layered gradient structure titanium plate,and the deformation and fracture of the fine crystal layer occur.The introduction of the coarse crystal layer passivates the crack tip through its plastic deformation,alleviates the localized deformation,and combines the particularity of the layered structure,thus hindering the further expansion of the crack and realizing the plastic effect.