Fabrication Of SiC Reinforced-ZTA Ceramics By Hot-Pressing Sintering Method And The Mechanisms

Al2O3 ceramics possess excellent properties such as high hardness,good wear resistance and very stable chemical properties and so on,but the low fracture toughness(3-4 MPa·m1/2)and low flexural strength(400-600 MPa)limit their applications.Therefore,it is very essential to reinforce Al2O3 ceramics,and synergistic toughening method are found to be more effective than single toughening method.In this thesis,SiC/ZTA composite ceramics with excellent mechanical properties were fabricated by hot-pressing sintering method using Al2O3 and 3Y-ZrO2 as raw materials,SiC whisker(SiCw)and SiC particle(SiCp)as reinforcement agents and MgO as sintering additive.The mechanical properties,microstructure and reinforcement mechanisms of the composite ceramics were investigated.Firstly,the effect of ball-milling time on the flexural strength of SiC/ZTA composite ceramics was investigated.The results showed that when the milling time increases,the flexural strength of the composite increases,and when the milling time increases to 10 h,the flexural strength of the composite tends to be stable.Secondly,the effects of sintering temperature,SiCw content and SiCp content on the mechanical properties of SiC/ZTA composite ceramic were investigated.It was found that as the sintering temperature increases from 1430? to 1630?,the Vickers hardness,relative density,flexural strength and fracture toughness of the composite ceramics increase firstly and then decrease,reaching the maximum values at 1530?.Therefore,the optimum sintering temperature for the SiC/ZTA composite ceramic is determined to be 1530?.When the content of SiCw increases from 0 to 26 wt%,the average grain size of the ceramics decreases from 752 to 296 nm.The flexural strength and fracture toughness of composite ceramic increase firstly and then decrease.When the content of SiCw is 20 wt%,the flexural strength reaches the maximum value of 1314.0 MPa.When the content of SiCw is 13 wt%,the fracture toughness reaches the maximum value of 14.7 MPa· m1/2.When the content of SiCp increases from 0 to 20 wt%,the average grain size of the ceramic decreases from 752 to 581 nm,and both the flexural strength and fracture toughness increase firstly and then decrease.When the content of SiCp is 13 wt%,the flexural strength and fracture toughness simultaneously reach the maximum values of 1180.0 MPa and 15.9 MPa·m1/2,respectively.The effects of the SiCw/SiCp ratios on the mechanical properties of SiCw/SiCp/ZTA composite ceramics were also investigated.The results showed that the Vickers hardness,flexural strength and fracture toughness of the ceramics increase firstly and then decrease with the increase of SiCw/SiCp ratio.When the SiCw/SiCp ratio increases from 0/20 to 16/4,the average grain size reduces significantly from 581 to 286 nm,and the flexural strength and fracture toughness simultaneously reached the maximum values of 1334.0 MPa and 16.0 MPa·m1/2,respectively.When the SiCw/SiCp ratio is 20/0,the average grain size increases instead and the flexural strength and fracture toughness degrade simultaneously.Finally,the toughening mechanisms in the composite ceramics were studied.It was found that the improvement of mechanical properties of SiC/ZTA composite ceramics can be mainly attributed to the phase transformation toughening of ZrO2,the pull-out and bridging of SiCw,the crack deflection and transgranular fracture of SiCp,grain refinement effect and their synergistic effects.