| ZTA ceramics is a widely used high-performance structural ceramic material for excellent properties such as corrosion and wear resistance,high hardness as well as cost-effective.The introduction of nano powders and TiC into ZTA can further improve its mechanical properties,however,due to the strong covalent bond of TiC,the sintering of ZTA/TiC composite ceramics often requires high sintering temperature or special sintering equipment,which has become an important factor to restrict its cost reduction.In order to avoid the presence of glass phase in traditional liquid additives to reduce the mechanical properties of ZTA ceramics,the glass-state materials blast furnace slag?BFS?with crystallization characteristics was added as sintering aid,which not only reduced the sintering temperature,but also improved the mechanical properties of ceramics.?1?Effect of hot pressing sintering temperature on properties of ZTA ceramics prepared by adding nano-Al2O3.55 wt.%of?-Al2O3,15 wt.%of nano-Al2O3 and 30wt.%of nano-Zr O2 were mixed by ball grinding,and sintered at 1550-1700?for 30min.The effect of sintering temperature on the physical and mechanical properties of composite ceramics was investigated.The results show that grain size of ZTA ceramics increased,porosity decreased and grain binding became denser with the increasing of temperature.Adding 15 wt.%of nano-?-Al2O3 can improve the sintering density and mechanical properties of ZTA ceramics.Relative density of ZTA ceramics sintered at1650?is 99.8%,and apparent porosity is 0.1%.Flexural strength,fracture toughness and Vickers hardness are 907 MPa,5.15 MPa m1/2 and 19.06 GPa,respectively.The fracture mode of ZTA ceramics is intergranular fracture and transcrystalline rupture with obvious cleavage,which make composite ceramics possess better mechanical properties.?2?ZTA/TiC composite ceramics was prepared by introducing nano-TiC.Above-mentioned ZTA matrix?70 wt.%Al2O3 and 30 wt.%Zr O2?was added 2-8 wt.%of nano-TiC and sintered at 1650?for 30 min.Effect of nano-TiC contents on the properties and microstructure was investigated.The results show that relative density of composite ceramics can reach 99.5%and apparent porosity is only 0.2%with 2 wt.%of nano-TiC added.Flexural strength,fracture toughness as well as Vickers hardness are 615 MPa,5.58 MPa·m1/2 and 18.89 GPa,respectively.Because TiC and Al2O3 have similar elastic modulus,a small amount of nano-TiC addition would increase the binding effect on t-Zr O2.The addition can improve stability of composites and inhibit martensitic transformation of t-Zr O2 grains,and strengthen its transformation toughening effect on Al2O3.The process factors and matrix content of Al2O3?70 wt.%?remained,and effects of nano-TiC and Zr O2contents on properties of ZTA/TiC composite ceramics were further investigated.The results show that the diffraction peak of TiC phase in composite ceramics gradually increases,while the diffraction peak of t-Zr O2 gradually weakens,and phase of m-Zr O2 appears with increasing content ratio of nano-TiC and Zr O2.During the cooling process,the thermal expansion mismatch between TiC and Al2O3 leads to a large amount of residual stress in sintered mass,which promotes martensitic transformation of t-Zr O2.Therefore,excessive nano-TiC adversely affects the mechanical properties of ZTA/TiC composites.?3?Pretreatment and performance analysis of BFS.After BFS was milled by high-energy ball grinding for 30 min,the particles below 5?m were taken and placed properly after drying.XRF,XRD,DSC and SEM were used to analyze the chemical composition,phase composition,thermal performance and microstructure of BFS powder.The results show that BFS is glassy material,which contains a variety of silicate components such as Ca O,Al2O3 and Si O2 as well as a small amount of crystallization nucleating agents such as Fe2O3,Ti O2 and Zr O2.After BFS was heat treated at 855?for 1 h,the crystal phase of Ca2Al2Si O7 about 1?m could be nucleated and crystallized,which indicates that BFS has high crystallization activity.?4?In order to decrease sintering temperature and enhance mechanical properties of ZTA/TiC composites,adding BFS with crystallization characteristics as sintering aids and investigating effect of BFS contents on the properties of two groups of ZTA/TiC composite ceramics.The results show that the addition amount of BFS in ZTA/TiC composite ceramics with TiC?2 wt.%?reaches 4 wt.%,the mechanical properties of composite materials are significantly improved after sintered at 1550?for 30 min.Flexural strength is 650 MPa,and fracture toughness is 6.03 MPa·m1/2.There are 15%and 14.2%higher than that at the same sintering temperature without addition of BFS.Adding 4 wt.%of BFS into ZTA/TiC composite ceramics with TiC?5wt.%?,sintered at 1550?for 30 min.Relative density of composite ceramics is 99.5%,and apparent porosity is 0.1%.Flexural strength,fracture toughness and hardness of composite ceramics are 555 MPa,5.2MPa·m1/2 and 17.88 GPa,respectively.There are26.7%,9.5%and 6.3%higher than that at the same sintering temperature without addition of BFS,and sintering temperature is reduced by more than 50?.Liquid phase produced by BFS in sintering process promotes the growth of Al2O3 rod crystal.During the process of stress,rod crystal extraction and crack deflection are conducive to the betterment of mechanical properties of composites.The crystallization of BFS at high temperature enhances the grain boundary strength and further builds up the mechanical properties of composite ceramics. |
PDF Full Text Request