Effect of volume ratio on optical and mechanical properties of Y2O3-MgO composites fabricated by spark-plasma-sintering process

Abstract The effect of Y2O3:MgO ratio on the microstructures, optical and mechanical properties of the Y2O3-MgO composites were investigated. Although the dense Y2O3-MgO composites were successfully fabricated in various Y2O3:MgO ratios using the spark-plasma-sintering (SPS) technique, the Y2O3:MgO ratio significantly influenced the microstructures and the optical/mechanical properties of the composites. Fine grain size was obtained in the composite with Y2O3:MgO = 50:50 owing to the effective pinning force caused by the homogenous two phase microstructure. The SPSed dense composites showed good transmittance in the wide wavelength range from visible to infrared (IR). The monolithic Y2O3 polycrystal, that is Y2O3:MgO = 100:0, showed the highest transmittance of 62.3% at 600 nm and 84.3% at 5 μm. Although the IR transmittance is independent of the Y2O3:MgO ratio, the visible transmittance decreased with the MgO particle dispersion. Among the Y2O3-MgO composites, the higher visible transmittance was obtained in the composite with Y2O3:MgO = 50:50 than those of the other two composites with Y2O3:MgO = 30:70 and 70:30 due to its smallest grain size. In contrast to the transmittance, the hardness Hv and toughness KIC tend to increase with increasing the MgO fraction irrespective of the grain size; both Hv and KIC increased from 9.6 GPa and 1.1 MPa m1/2 for the monolithic Y2O3 to 12.7 GPa and 2.5 MPa m1/2 for the composite with Y2O3/MgO = 30:70, respectively. The enhanced hardness and toughness of the composite can be interpreted dominantly by the mixture rule as a function of the volume fraction of the MgO phase.