Microstructure, mechanical properties and ultra-high temperature thermal stability of GdB6 ceramics fabricated by reactive spark plasma sintering

In this study, a highly dense GdB6 bulk ceramic material was fabricated using one-step in-situ reaction spark plasma sintering technology. The sample with a relative density of 96.7 % and a purity of 96.9 wt% was successfully obtained by sintering at 1800 degrees C for 30 min under a uniaxial pressure of 50 MPa. The Vickers hardness, elastic modulus and fracture toughness of the as-obtained GdB6 bulk ceramics were 18.9 GPa, 209 GPa and 1.6 MPa & sdot;m1/2, respectively. The thermal conductivity of GdB6 at room temperature was 28.68 W & sdot;m- 1 & sdot;K-1, 70 % of which was mainly attributed to phonon vibration, while the remaining 30 % to the electrical thermal conductivity. In addition, the as-obtained GdB6 ceramics showed no phase transformation after heat treatment at a relatively high temperature of 2100 degrees C for 20 min in Ar atmosphere. The highly covalent octahedral boron framework played a critical role in maintaining the phase stability of the GdB6 crystal lattice. This suggested that GdB6 ceramics could be used as potential ultra-high temperature ceramics for aerospace applications and highpower vacuum electronic devices operated at high temperatures.