National Defense Academy, School of Systems Engineering, Department of Mechanical Engineering, Yokosuka 239-8686
Mechanically alloyed amorphous ceramic powders with a chemical composition of (ZrO2-3 mol%Y2O3)-26.2 mol%SiO2-3.4 mol%CeO2 have been prepared by a planetary ball mill. Thermal differential analysis (DTA) experiments show that the onset temperature of crystallization increases from 1071 to 1105 K as the heating rate increases from 5 to 50 K/min. These amorphous powders have been consolidated at the heating rate of 480 K/min under the applied stress of 150 MPa in a chamber evacuated to 10 Pa, using an electrical discharge consolidation system. After the formation of tetragonal zirconia solid solution, marked increase in the relative density occurs in the narrow temperature range from 1178 to 1315 K. The fully dense bulk sample sintered at 1315 K consists of tetragonal (or tetragonal+cubic) zirconia solid solution together with amorphous silica. The average crystallite size increases from 10 to 15 nm as the consolidation temperature increases from 1223 to 1315 K. Moreover, the isothermal consolidation treatment for about 700 s causes further increase in the crystallite size by a factor of two, regardless of the consolidation temperature. These results indicate that the crystallite size can be widely changed (10 ∼ 30 nm) by controlling the consolidation temperature and the isothermal consolidation period of time.
ball milling, mechanical alloying, solid state amorphization, amorphous powder, electrical discharge consolidation, ZrO2-SiO_2-CeO2-Y2O3 system, zirconia solid solution, nanostructure
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