Preparation, sintering and fracture behavior of Al_(2)O_(3)/LaAl_(11)O_(18) ceramic composites

摘要

Al_(2)O_(3)/25 vol% LaAl_(11)O_(18) composites were prepared by pressureless sintering at 1550℃ with composite powders obtained by copercipiated method using La(NO_(3))·6H_(2)O and Al(NO_(3))_(3)·9H_(2)O as starting materials. The enhanced reactive activity of Al_(2)O_(3) and chemically homogeneous mixing of the constituents made LaAl_(11)O_(18) phase to be formed at low temperature in composite powders. AlF_(3) additive was used to reduce the transformation temperature of transition alumina. The LaAl_(11)O_(18) grains in the composite powder obtained at 1500℃ showed rodlike morphology distributed homogeneously in Al_(2)O_(3) powder. The samples sintered at 1550℃ for 4 h with CAS (CaO-Al_(2)O_(3)-SiO_(2)) sintering aid can obtain a high relative density. The effects of the sintering time on the grain growth of Al_(2)O_(3) and the fracture toughness of the composites were studied and the results showed that LaAl_(11)O_(18) grains reduced the growth of Al_(2)O_(3) grains and the rodlike grains increased the fracture toughness. The improvement in fracture toughness of the composites was mainly attributed to the mechanism of crack deflection.