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*Email: ikedaj@jmmc.jpHigh purity alumina (Alumina) and 3 mol% yttria stabilized tetragonal zirconia polycrystalline(3Y-TZP) have been used for hip and knee joint prostheses because of their excellent wearproperty and biocompatibility. Especially, Ceramic-on-ceramic bearing has been applicableeven to younger patients. Recently, various alumina and zirconia composites were developedand proposed as alternatives to Alumina and 3Y-TZP. It was reported that alumina and zirconiacomposites have superior mechanical properties compared with Alumina. However, it was alsoreported that changes in crystal structure of zirconia phase in some alumina and zirconiacomposites including commercially available zirconia toughened alumina (ZTA) underhydrothermal environment such as human body occurred. Consequently, it is necessary forlonger reliability to improve not only mechanical properties but phase stability of zirconia phaseconcurrently. In our previous study, it was confirmed that newly-developed ZTA(BIOCERAM ® AZ209) had good mechanical properties compared with Alumna. However, therelationship among mechanical and wear properties, phase stability and microstructure ofBIOCERAM ® AZ209 is still unclear. In this study, we evaluated these characteristics ofBIOCERAM ® AZ209 with different microstructures.BIOCERAM ® AZ209 powder, which composed of Al 2 O 3 (79 wt %), ZrO 2 (19 wt %) and otheroxides (2 wt %), were pressed into the solid form. Green bodies were sintered at varioustemperatures in air and then HIP (hot isotopic press) treatment was subjected. The densespecimens with over 99.9% of theoretical density were turned to prescribed shapes and fivekinds specimens with several grain sizes and crystal structures were prepared. Microstructuresof sintered bodies were checked by scanning electron microscope (SEM) and X-raydiffractometer. Mechanical properties were evaluated according to ISO standards. Besides,phase stability under hydrothermal environment and specific wear rate in ceramic-on-ceramiccombination were evaluated. Alumina manufactured by Japan Medical Materials Corporationwas used as comparative material of each evaluation.In SEM observation, homogeneously dispersion of zirconia grains in alumina matrix and noagglomeration of zirconia grains were observed. From the result of X-ray diffraction,monoclinic fraction of zirconia phase was calculated by Garvie and Nicholson equation.Increases in both grain size and monoclinic fraction with increasing sintering temperature wereobserved. Besides, with increasing sintering temperature, fracture strength was declined fromabout 1300 to < 500 MPa and fracture toughness was increased from 3.8 to 5.0 MPa·m 1/2 . Bothgrain size and stress induced phase transformation affected the fracture strength ofBIOCERAM ® AZ209, and the effect was larger in the former than in the latter. In allspecimens, no significant change in crystal structure in saturated vapor at 134 °C was observed.It was confirmed that zirconia phase of BIOCERAM ® AZ209 was stable as well as Aluminaunder hydrothermal environment. It was possible to support mechanical properties and phasestability at the same time. The relationship between wear property with squeaking under highload condition and mechanical properties will also be discussed in terms of microstructure ofBIOCERAM ® AZ209.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]