Formation Control And Growth Kinetics Of "Intragranular" ZrO₂/Al₂O₃ Composite Ceramic

Al₂O₃ ceramics are widely used as important engineering materials in many aspects.However,the inherent high brittleness of Al₂O₃ ceramics has restricted its application and development.In structural ceramics,the introduction of nano-scale second-phase particles into a micro-scale matrix limits the mass transfer between phases during the sintering process,and the growth of particles is suppressed,so that it exists in the nano-state in the body to make nanocomposite ceramics has become one of the ways to improve the mechanical properties of ceramics.Adding nano-Zr O₂ to Al₂O₃ ceramic matrix can improve the flexural strength and fracture toughness of Al₂O₃-based composite ceramics to a certain extent.Relevant research shows that the existence of"intragranular"structure in the ceramic matrix can greatly improve the performance of composite ceramics.However,there are few reports on the research results of the"intragranular"structure of the nanophase that can effectively control the dispersion distribution.There is no stable and mature process method for the formation control of the"intragranular"structure,and the mechanism of strengthening and toughening the composite ceramics has not been well explained.The author adopted a simple new method—mechanical grinding dispersion method—was used to prepare a nano-Zr O₂/Al₂O₃ composite ceramic that was uniformly mixed and contained a large number of"intragranular"structures without using dispersants.The influence of Zr O₂ content changes,different preparation methods of the composite powder and sintering processes on the formation of the"intragranular"structure and mechanical properties of composite ceramics were investigated;The effect of the"intragranular"on the grain growth kinetics of Zr O₂/Al₂O₃ composite ceramics was analyzed;The strengthening and toughening mechanism of the"intragranular"structure of Zr O₂/Al₂O₃ composite ceramics is discussed.The results show that the 3vol.%Zr O₂/Al₂O₃ composite powder prepared by mechanical grinding and dispersion method contains a lot of"intragranular"structure in the composite ceramics obtained by microwave sintering at 1500℃for 30min.The relative density,flexural strength,fracture toughness,and Vickers hardness of 3vol.%Zr O₂/Al₂O₃ composite ceramics prepared by this method are 99.07%,520.21MPa,7.64MPa·m^1/2 and 18.79GPa,in which the flexural strength and fracture toughness are increased by 50%and 83%co MPared to 3vol.%Zr O₂/Al₂O₃ composite ceramics prepared by the traditional direct doped Zr O₂ powder method.The formation of the"intragranular"structure is affected by the preparation method of the composite powder,the content of Zr O₂ and the sintering process.When the composite ceramic contains3vol.%Zr O₂,the number of the"intragranular"reaches the maximum.The grain growth kinetics index n and growth activation energy Q of Zr O₂/Al₂O₃ composite ceramics also increase and then decrease with the increase of Zr O₂ content,and the n and Q values of long axis and short axis of Al₂O₃ grains reach the maximum when Zr O₂ content is 3 vol.%.The"intragranular"Zr O₂ particles were dispersedly distributed in the Al₂O₃ ceramic matrix to form a superlattice structure,and there was a coherent relationship between the two interfaces.The interaction of the coherent dispersion phase and dislocations,crack deflection,bridging,and the pull-out of"intragranular"Zr O₂ grains are the main strengthening and toughening mechanisms of Zr O₂/Al₂O₃composite ceramic materials.Compared with the Zr O₂ phase transformation and toughening effect in the composite ceramic prepared by traditional direct doped Zr O₂powder method,the effect of coherent dispersion phase on the toughening effect of the composite ceramic is more prominent.