セリア添加ジルコニア多結晶体の還元熱処理による強化機構

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The strengthening mechanism of 12 mol%CeO_2-doped tetragonal zirconia polycrystals (12Ce・TZP) after reduction at 600 to 1000℃ in hydrogen gas was investigated from the viewpoints of crystal phase, hardness, bending strength and residual stress by X-ray analysis. Weight loss as well as color change were recognized in the reduced Ce-TZP, where oxygen release was caused by the reduction of Ce^<4+> to Ce^<3+>. In the tetragonal phase after reduction heat treatment. The tetragonality decreased and the lattice volume increased by 1%,which is due to the increase in ionic radius of Ce^<4+> to Ce^<3+>. The highest hardness value of 12.8 Gpa was obtained on the surface of an entirely reduced 12Ce・TZP. When only the surface layer was reduced by heattreatment for short time, the 12Ce・TZP specimen showed a maximum bending strength of 750 Mpa, higher than as-received specimen by approximately 40%. No stress induced transformation from tetragonal to monoclinic phase was observed near the surface of reduced 12Ce-TZP after bending test. A good correlation between bending strength and residual stress in tetragonal phase evaluated by X-ray stress measurement, was confirmed. A residual compressive stress of approximately 400MPa was introduced in the surface of the most strengthened specimen. Partial reduction of 12Ce-TZP under selected conditions introduced residual compressive stress in a surface layer of the polycrystals and led to strengthening of the ceramic. In this work,the authors proposed a novel mechanism of "reduction-induced strengthening (RIS)"in CeO_2 containing ceramics.
社団法人日本セラミックス協会の論文
2003-04-01

セリア添加ジルコニア多結晶体の還元熱処理による強化機構

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