Consolidation and high‐temperature strength of monolithic lanthanum hexaboride

In this study we explored the densification, microstructure evolution, and high‐temperature properties of bulk lanthanum hexaboride. LaB6 bulks were consolidated using spark‐plasma sintering only in the temperature range between 1400°C and 1700°C. We adopted flash spark plasma sintering (SPS) of LaB6 using a direct current heating without a graphite die. We observed a peculiar grain‐size gradient when coarse grains exceeding 300 μm were observed on the top side of the specimen, while the bottom side had a grain size of 15–20 μm. Such large grain was not observed using SPS at 2000°C, suggesting that these might originate from a local overheating. Based on the three‐point flexural tests, it was observed that the toughness and strength of the LaB6 were acceptable at room‐temperature (3.1 ± 0.2 MPa m1/2, 300 ± 20 MPa). However, at 1600°C, these parameters would decrease to 1.3 ± 0.1 MPa m1/2 and 120 ± 40 MPa, respectively.