Mechanical Properties Of Graphene Nano-Platelets Reinforced Zirconia Ceramics Fabricated By Field Assisted Sintering Technique

Zirconia ceramics is widely used in refractory materials,structural materials,functional materials field et al.due to its excellent mechanical properties such as fracture toughness,flexural strength,good thermal stability at high temperature,heat insulation,resistance to corrosion,low thermal conductivity and comparable to that of metal thermal expansion coefficient.Using traditional sintering method,there exists ununiform phase and structure,low density,small sintering power and low mechanical properties problems to make it difficult to meet the requirement of modern science and technology.Therefore,it is of great practical value to fabricate high density,single phase and high mechanical properties zirconia composites.In this paper,it is proposed to add GNPs to strengthen and toughen zirconia composite ceramics because graphene nano-platelets?GNPs?have high flexural strength and tensile strength.Firstly,the effects of dispersant types on GNPs dispersion were studied and GNPs/3Y-TZP composite powder was produced.Secondly,Plasma Activated Sintering technique was applied to prepare GNPs/3Y-TZP composite ceramics with high density,single phase,homogeneous dispersion of GNPs.Finally,the relationship between the microstructure and mechanical properties and its toughening mechanism were discussed.The absorbance of GNPs in the DMF was the largest.Hansen parameters??p+?h?25 and the[NH₂?CH₃?₂]⁺¹ group have positive effect on the uniformity and stability of GNP.The CH and OH groups exist in GNPs,the defect density increased and 3Y-TZP particle size decreased after ultrasonic and ball milling.Low temperature densification of GNPs/3Y-TZP achieved by plasma activated sintering technology.Under 1300 ^oC,30 MPa,3 min sintering conditions,the defect density of GNPs increased and the relative density was up to 99.72%.All the samples were single tetragonal phase and GNPs evenly distributed in the grain boundaries of 3Y-TZP.It is found that the fracture toughness of 0.01 wt.%GNPs/3Y-TZP was up to15.6 MPa?m^1/2,increase 61.6%compared with 3Y-TZP.The highest flexural strength reached 1200.8 MPa,increased 31.3%.The study founds that GNPs show significant toughening effect on the 3Y-TZP composite ceramics and the main toughening mechanism is graphene pull-out,bridging,crack deflection and branching,micro cracks et al.The stress of composite interface was calculated by using the existing model.The critical length of GNPs to toughen 3Y-TZP was obtained.At the same time the residual thermal stress of the GNPs is calculated.The effect of residual thermal stress on the mechanical properties of 3Y-TZP composite ceramics could be inegligible.