High temperature properties of B6O-materials

B6O is a potential superhard material with a hardness of 45 GPa measured on single crystals. Recently it was found that different oxides can be utilized as an effective sintering additive which allows densification under low pressures. In this work the effect of addition of Y2O3/Al2O3 on high temperature properties was investigated using impulse excitation technique (IET), hardness measurements and dilatometric measurements. The IET technique reveals the softening of the residual B2O3 in the materials without additives at 450 °C; in the materials with Y2O3/Al2O3 the softening is observed at only about 800 °C. This data agrees with the values found for different borate glasses.The materials showed no pronounced reduction of hardness at these temperatures. This is additional evidence, supporting previous observations that the material consists of pure grain boundaries between B6O grains. Hardness values (HV5) of up to 17 GPa at 1000 °C were observed.