Low Temperature And High Strain Rate Superplastic Deformation Of Zirconia Ceramics Assisted By Electric Field

Structural ceramic materials with a series of excellent properties are closely related to many modern emerging science and technology.However,due to the inherent brittleness of ceramic materials,it is difficult to use traditional plastic processing to form complex high-precision ceramic parts,which restricts the development of engineering ceramic materials to a large extent.The research on the high strain rate superplastic deformation of structural ceramics at low temperature can provide a new direction for the machining of precision ceramic parts.In this thesis,the low temperature and high tensile velocity superplastic deformation behavior of 3YSZ ceramics assisted by AC electric field,the microstructure evolution and possible deformation mechanism were systematically studied by constant rate and constant load tensile test and microstructure analysis.The mechanical properties of 3YSZ ceramics before and after high strain rate deformation were tested.The main results are as follows:（1）The superplastic deformation temperature of 3YSZ ceramics was reduced to 700℃assisted by AC electric field with the current density of 160～240 m A·mm^-2,and the elongation of 3YSZ ceramics was more than 400%in the range of the strain rate of 10^-3～10^-2 s^-1.Compared with the traditional superplastic deformation under the temperature and stress field,the flow stress is significantly reduced by the electric field assisted deformation,which is related to the conductive characteristics of the specimen in the process of AC electric field assisted deformation.（2）During constant strain rate tensile deformation,The initial flow stress decreases with the increase of current density and frequency,and the elongation increases with the increase of AC electric field frequency.The degree of stress reduction at the initial stage of deformation increases with the increase of strain rate and decreases with the increase of current density.During constant load tensile deformation,the elongation and strain rate first increase and then decrease with the increase of current density.（3）The phase before and after deformation is consistent and is tetragonal.The grain shape before and after deformation is equiaxed.In the initial stage of stress reduction,the number of pores and relative density increase and decrease respectively with the increase of strain;with the increase of strain,after entering the stable deformation stage,the number of pores and relative density will gradually decrease and increase;The mechanical properties（hardness,fracture toughness）after high tensile velocity deformation to stable deformation stage did not significantly decrease.（4）Using the relevant data in the deformation curve,it is calculated that the stress index is between 1.7 and 3,and the deformation activation energy is similar to the grain boundary diffusion activation energy of Zr⁴⁺.It is speculated that the possible mechanism of the low temperature and high strain rate superplastic deformation of 3YSZ ceramics assisted by AC electric field is grain boundary slip coordinated by diffusion and dislocation motion,and the deformation activation energy is similar to the grain boundary diffusion activation energy of Zr⁴⁺,and the deformation rate is controlled by the diffusion of Zr⁴⁺along the grain boundary.