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

In this study, a highly dense GdB 6 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 °C for 30 min under a uniaxial pressure of 50 MPa. The Vickers hardness , elastic modulus and fracture toughness of the as-obtained GdB 6 bulk ceramics were 18.9 GPa, 209 GPa and 1.6 MPa·m 1/2 , respectively. The thermal conductivity of GdB 6 at room temperature was 28.68 W·m −1 ·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 GdB 6 ceramics showed no phase transformation after heat treatment at a relatively high temperature of 2100 °C for 20 min in Ar atmosphere. The highly covalent octahedral boron framework played a critical role in maintaining the phase stability of the GdB 6 crystal lattice . This suggested that GdB 6 ceramics could be used as potential ultra-high temperature ceramics for aerospace applications and high-power vacuum electronic devices operated at high temperatures.