Reaction sintering of $Al_{2}-O_{3}-ZrO_{2}_Nb$ composite has been investigated using $Al_{2}O_{3}$,$Nb_{2}O_{5}$ and $ZrAl_{2}$ powders. During sintering, a reaction between $Nb_{2}O_{5}$ and $ZrAl_{2}$ occurs and results in the formation of $ZrO_{2}$ and Nb in alumina matrix. Two series of specimens, $78.32Al_{2}O_{3}-14.02Nb_{2}O_{5}-7.66ZrAl_{2}$ in wt% (AZN-5), and $72.34Al_{2}O_{3}-13.76Nb_{2}O_{5}-7.52ZrAl_{2}-6.38ZrO_{2}(AZN-10)$,have been prepared. After the reaction, AZN-5 specimen contains 5vol% $ZrO_2$ and 4.99vol% Nb, and AZN-10 specimen 10vol% $ZrO_2$ and 4.99vol% Nb. Powder compacts have been sintered at various temperatures between 1600 and 1700℃ for 30min in Ar. DTA and X-ray analysis have shown that the reaction started at 1490℃.
Sintered density increases with sintering temperature. AZN-10 specimen shows highter density than AZN-5 specimen for almost all the experimental conditions. Hot pressed and reaction sintered $Al_2-O_3-ZrO_2-Nb$ show higher toughness and lower hardness than hot pressed $Al_2-O_3-ZrO_2$. The toughness difference increases with $ZrO_2$ content. During the toughness measurement by the indentation method, the crack propagates through many metallic Nb particles which show ductile deformation. The increase in toughness of $Al_2-O_3-ZrO_2-Nb$ over $Al_2-O_3-ZrO_2$ is believed to result from the absorption of crack propagation energy by the plastic deformation of Nb particles.
