Study On Preparation And Properties Of Layered Composite ZrO₂ Ceramics

The layered structure of ZrO₂ composite was prepared by non aqueous tape casting technology and ZrO₂ laminated pressureless sintering method,which used the nano-zirconia as ceramic matrix,alμmina as ceramic reinforced phase,absolute ethyl alcohol as solvent,PVB as binder,DBP as plasticizer.Firstly the influence of variables on the properties of ZrO₂ casting slurry and green film were studied,and so were the ZrO₂-Al₂O₃ composite slurry and composite green film.At the same time,morphology of the green film was characterized by scanning electron microscopy.Then a reasonable debinding processe was established according to the thermo-gravimetric（TG）analysis of green substrate.At last,the layered structure of ZrO₂ composite was prepared by stack,cold pressing,plastic drainage and pressureless sintering method.The properties of layered ceramics were characterized by using relative density,bending strength,fracture toughness,hardness and SEM.And the toughening mechanism of layered structure was put forward.The results showed that when the amount of solvent ethanol was 100g,the addition of zirconia ceramic power was 90g,and the ratio of plasticizer and binder was 0.6,a good stability,submicron-zirconia slurry of tape casting could be gained and the viscosity of which was 7.5Pa.s.And the density and the tensile strength and elongation at break of the green zirconia ceramic substrate were 3.43g/cm3、9.8MPa、36.1%respectively.Then taking 15wt%Al₂O₃ as the second phase instead of ZrO₂,the ZrO₂-Al₂O₃ composite green substrates could be gained,and the density and the tensile strength and elongation at break of the green substrates were 2.88g/cm3、8.41MPa、61.82%respectively.SEM electron microscope photos results showed that PVB polymer membrane uniformly wrapping up ceramic particle surface and the homogenous distribution of ceramic particle without the obvious bigger pores.The reasonable debinding process of zirconia green cast film and zirconia-alμmina composite green films were established according to the TG analysis of green substrate.Then green ZrO₂ films were sintered at different sintering temperatures.By comparing the performance,sintering temperature of 1500℃ and sintering time of 120 min were optimized.In this sintering process,ZrO₂ ceramic substrate of relative density up to 98.03%was prepared with fine particles and uniform distribution of particles between the close packing,and ZrO₂-Al₂O₃ ceramic substrate of relative density up to 98.95%was prepared with the second phase Al₂O₃ particles closely combined with the matrix phase ZrO₂ ceramic particles.The ZrO₂/ZrO₂-Al₂O₃ cast film laminated composite ceramics were prepared by pressure sintering process,and the effect of Al₂O₃ content on properties were studied.The results showed that when the Al₂O₃ content in the heterogeneous phase was 10wt%,the hardness and bending strength of the laminated composite ZrO₂ ceramics were the best,which were 12.75GPa,750MPa,respectively;When the Al₂O₃ content in the heterogeneous phase was 15wt%,the fracture toughness of the composite ZrO₂ ceramic was as high as 16.57MPa.m1/2.Through the analysis of strength and toughness of ZrO₂/ZrO₂-Al₂O₃ composite ceramics,we could find that the lamellar structure changed the crack propagation path,which was beneficial to the improvement of toughness,and the mechanism was residual stress in strong interfacial layer,resulting in energy absorption,transfer and consumption.Meanwhile,the addition of the second phase Al₂O₃ in the ZrO₂ ceramics could play the role of particle dispersion toughening.