Synthesis and Characterization of <scp> YB ₄ </scp> Ceramics

Abstract

Yttrium tetraboride was synthesized by reactions of Y 2 O 3 with B 4 C or with a B 4 C/C mixture. Fully dense YB 4 ceramics were prepared by hot‐pressing at 1800°C and 20 MPa in He . The flexural strength and microhardness of the YB 4 were about 300 MPa and 27 GPa, respectively. Pure YB 4 showed considerable oxidation above 1200°C. The effect of SiC, AlN, and AlN/SiC on the properties of YB 4 ceramics was characterized. No chemical interactions were identified in the YB 4 –SiC and YB 4 –AlN pseudo binaries. The addition of SiC improved the oxidation resistance below 1200°C. At higher temperatures, the low viscosity of a surface melt caused its continuous runoff and the loss of the oxidation‐protection capability of the scale. The addition of AlN/SiC improved the oxidation resistance compared to the ceramics containing only SiC , which was attributed to the presence of Al 2 O 3 in the Y 2 O 3 –SiO 2 –B 2 O 3 glass leading to an increase in its viscosity and preventing glass runoff. A significant improvement in the oxidation resistance of the YB 4 ceramics and extension of their oxidation stability to 1400°C was accomplished by the introduction of AlN only.