Research On Microstructure And Superplastic Deformation Of 3Y-TZP Ceramics

3Y-TZP ceramic has excellent hardness,strength,insulation and corrosion resistance.It also has good fracture toughness,thermal stability and chemical stability.So it is commonly used in the manufacture of extreme conditions,and it has a broad application prospect in the defense,machinery,aerospace and other fields.However,brittleness and hard machining have limited the application of ceramic materials,and it has been an urgent problem to obtain ceramic materials with better comprehensive properties.The superplastic characteristics of ceramic materials can make the plastic processing of precision ceramics a reality,which provides a new way for the development and application of ceramic materials.This paper studies the preparation of 3Y-TZP ceramics,and doping graphene nanosheets to improve the fracture toughness of the materials was also investigated.The deformation behavior and deformation mechanism of 3Y-TZP and graphene toughened TZP were studied through the superplastic compression experiment.The main results are as follows:With the increase of the hot-pressing sintering temperature,the grain size of the specimens increased,the porosity decreased,the fracture mode changed from intergranular fracture into mixed fracture.The hardness reached the maximum value 13.24 GPa near 1350?,and the flexural strength and fracture toughness increased with the increase of the sintering temperature.When the spark plasma sintering temperature is 1350?,the highest fracture toughness value 11.04 MPa·m1/2 was obtained.These two kinds of sintering methods both could obtain tetragonal zirconia.The specimens sintered by hot pressing were more compact,and the higher fracture toughness value and smaller grain size could be obtained by spark plasma sintering.GNP/3Y-TZP composite powder was prepared by ball-milling.Graphene uniformly dispersed in the matrix through the observation of the section,but graphene agglomeration increased gradually with the increase of the content of graphene.The density and hardness of the composite ceramics were slightly reduced,and the fracture toughness value was highest when the content of graphene was 1%,which increased by about 17% comparing with 3Y-TZP ceramics.It was found that the machinability of GNP/3Y-TZP composite ceramics increased continuously with the increase of the content of graphene.The superplastic deformation ability of 3Y-TZP ceramics doped with graphene was improved,and the main reasons were the energy absorption of graphene and the inhibition of the growth of zirconia grain during deformation.The compression tests of 3Y-TZP ceramics showed that the deformation resistance of 3Y-TZP decreased with the increase of the punch velocity,as well as the deforming temperature.The grain size increased after deformation,while the grains remained equiaxed.The stress-jump deformation was conducted at 1250?.The experimental results were consistent with the classical flowing law for superplastic ceramics.The stress exponents were measured as a function of the grain size.It was found that the stress exponent increased with the decrease of grain size in a certain range.When the stress is 30 MPa,the deformation activation energy of 3Y-TZP ceramics was 627 kJ/mol.Based on the deformation behavior,characteristic values and microstructure of the material,the main deformation mechanism of the 3Y-TZP was grain boundary sliding accompanied by the diffusion.