Flash Sintering Of Al₂O₃-based Eutectic Ceramic

Al₂O₃-based eutectic ceramics have excellent antioxidant properties,corrosion resistance and high-temperature structural stability,which have broad application prospects in the aerospace field.Currently,eutectic ceramics preparation techniques are mainly focused on Bridgman method,micro-drawing method and laser floating zone melting method.However,these methods require high preparation temperature and expensive equipment.Thus the development of new techniques for preparation of eutectic ceramic with simple processes and low energy consumption is highly valuable to promote their industrial applications.Flash sintering is a new electric field/current-assisted sintering technology having the advantages of high energy efficiency and simple process,which has attracted much attention.Al₂O₃-GAP（Gd AlO₃）-ZrO₂ ceramic powders were prepared by polyacrylamide gel method,and then pressed into dog-bone shaped green compacts by dry pressing technique.The sintering behavior was studied by regulating the electric field and limiting current.The results showed that flash sintering occurred in the range of 1317-1363°C at electric field of500-800 V/cm and the current limit of 100 m A.The irregular eutectic structure was formed after the flash sintering.The flash sintering temperature decreased as the electric field increased,but having no significant effect on the eutectic structure.The current limit has less effect on the flash sintering temperature,but has a significant influence on the eutectic structure.When the current limit was 60 m A,there was no eutectic structure formed in the sample.With the increase of current limit,the eutectic structure was gradually formed and changed from irregular eutectic to complex regular eutectic.The hardness and fracture toughness of the Al₂O₃-GAP-ZrO₂eutectic ceramics prepared by flash sintering was 17.7 GPa and 4.3 MPa·m^1/2,respectively.Al₂O₃,Gd₂O₃,and ZrO₂ powders prepared by polyacrylamide gel method were pressed into dog-bone shaped green compacts.The possibility of preparing Al₂O₃-GAP-ZrO₂eutectic ceramics by reactive flash sintering was investigated by applying different electric fields,current limits and holding time.It was found that flash sintering occurred in the range of911-994°C at electric field of 600-900 V/cm and current limit of 100 m A.The phase composition was transformed from Al₂O₃,Gd₂O₃,and ZrO₂into Al₂O₃,GAP and ZrO₂within10 s in flash sintering.Furthermore,the eutectic structure was formed.The hardness and the fracture toughness of the Al₂O₃-GAP-ZrO₂eutectic ceramics prepared by reactive flash sintering was 17.3 GPa and 4.4 MPa·m^1/2,respectively.The Al₂O₃and Gd₂O₃ ceramic powders prepared by polyacrylamide gel method were pressed into dog-bone shaped green compacts.Then an electric field of 800 V/cm and a current limit of 60-160 m A were applied to green compacts to investigate the possibility of preparing Al₂O₃-GAP eutectic ceramics by reactive flash sintering.It was found that flash sintering occurred in the range of 919-1001°C at a current limit of 60-160 m A and the electric field of 800 V/cm.The phase composition was transformed from Al₂O₃and Gd₂O₃into Al₂O₃and GAP in the flash sintering.The size of colony decreased with increase of the current limit.The hardness and the fracture toughness of the Al₂O₃-GAP eutectic ceramics prepared by reactive flash sintering was 17.6 GPa and 3.2 MPa·m^1/2,respectively.