Preparation And Mechanical Properties Of ZrO₂-Al₂O₃-SiC Composites By Oscillatory Pressure Sintering

Zirconia-based ceramics have been widely used in the fields of wear-resisting parts,cutting,semiconductors and electronics due to their excellent mechanical properties.With the development of modern key technology application fields and the demands of extreme application environments,the mechanical properties of zirconia-based ceramics,especially the fracture toughness,still need to be further improved.In general,the fracture toughness of zirconia-based ceramics is improved by adding a single reinforcing phase,while their mechanical properties are often reduced.In addition,pressureless sintering or static constant pressure sintering is often used to prepare zirconia-based ceramics,but their density and reliability are faced with some challenges.In view of the above problems,the alumina toughened zirconia ceramic was used as the matrix and silicon carbide whiskers(SiCw)and silicon carbide particles(SiCp)were used as the reinforcing phases in this work.In addition,the new dynamic oscillatory pressure sintering technique(OPS)was used to prepare ZrO₂-Al₂O₃-SiC composites with high strength,high toughness and high hardness.The research work mainly included the effect of material composition(single or composite introduction of SiCw and SiCp)and oscillatory pressure sintering temperature on the sintering behavior,microstructure and mechanical properties of such composites.Besides,the experimental results were compared with those of specimens preprared by hot pressing sintering and the mechanisms of synergistic strengthening and toughening of the composites were also revealed.According to the above research work,the following main conclusions can be drawn:(1)The fracture toughness of ZrO₂-Al₂O₃-SiCw composites could be significantly improved by the introduction of SiCw.It was found that the optimum sintering temperature was 1550 ?,the best added amount of SiCw was 15 vol.%.The mechanical properties of composites under these parameters by OPS were better.The reason was mainly that the oscillatory pressure could effectively avoid the agglomeration of whiskers,reduce the amounts and size of pores and thus improve the densification and mechanical properties of composites.The maximum fracture toughness of composites by OPS was 7.79 MPa?m^1/2.The main reason was the presence of some toughening mechanisms such as whisker pull-out,whisker bridging,crack branching and crack deflection in the composites,which increased the energy dissipation,and thus released more fracture energy.At the same time,the addition of Si C whiskers decreased the strength and hardness of the composites.(2)The addition of SiCp increased the hardness of ZrO₂-Al₂O₃-SiCp composites.It was found that the optimum sintering temperature was 1600 ?,the best SiCp particle size was 200 nm and the best added content of SiCp was 10 vol.%.Under these parameters,the density and mechanical properties of such composite were the best.The relative density,bending strength,Vickers hardness and fracture toughness were 98.63%,1162 MPa,15.43 GPa and 6.36 MPa?m^1/2respectively.In addition,when the time of low temperature aging experiment was 40 h,the m-ZrO₂ content in the composite containing 10 vol.%SiCp was ⁶ vol.%,which indicated that the composite had a good ability to inhibit low temperature aging behavior.(3)The introduction of SiCw and SiCp could keep the high strength and toughness of ZrO₂-Al₂O₃-SiC composites.Results showed that when the contents of SiCw and SiCp were 5 and10 vol.% respectively,the comprehensive properties of the composites were the best,in which vickers hardness was 15.26 GPa,bending strength was 917 MPa and fracture toughness was 6.83MPa?m^1/2.Due to the existence of synergistic toughening mechanism such as particle dispersion toughening,whisker toughening and stress-induced phase transformation toughening,the energy dissipation was increased.In addition,the phase boundaries of ZrO₂/SiCp,Al₂O₃/SiCp,ZrO₂/SiCw and Al₂O₃/SiCw were in the form of coherent relationship,which improved the plastic deformation ability of the composites.Moreover,it was found that the content of m-ZrO₂ in the composites containing 5 vol.%SiCw and 10 vol.%SiCp was low and almost unchanged with the increase of the low temperature aging time,indicating that the composites had good resistance against low temperature degradation.