PURPOSE: To provide the subject ceramic alloy of high toughness by including the stabilizer which mainly consists of ZrO2, etc., and contains the toughness increasing agent consisting of YNbO4, etc., of the prescribed quantity and the stabilizer consisting of YO1.5 so that the micro structure mainly comprises the crystals having the tetragonal structure.

CONSTITUTION: The ceramic alloy of high toughness contains (A) the main composition to be selected among ZrO2, ZrO2-HfO2 solid solution and HfO2, (B) 0.5-8 mol.% toughness increasing agent to be selected from among YNbO4, YTaO4, MNbO4, MTaO4 (where M means Mg, rare earth element, etc.), and (C) the stabilizer consisting of YO1.5. The mol.% of B composition and C composition is regulated so as to be the value within a polygon 0-P-Q-R-S-T-U-V-W-X- Y-Z-O in the coordinate system in the figure. In addition the ceramic toughness of high toughness is manufactured so that the micro structure of the alloy consists of the crystals mainly having the tetragonal structure.