Consolidation and high‐temperature strength of monolithic lanthanum hexaboride

Abstract

In this study we explored the densification, microstructure evolution, and hightemperature properties of bulk lanthanum hexaboride. LaB 6 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 LaB 6 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 LaB 6 were acceptable at room-temperature (3.1 ± 0.2 MPa m 1/2 , 300 ± 20 MPa). However, at 1600 • C, these parameters would decrease to 1.3 ± 0.1 MPa m 1/2 and 120 ± 40 MPa, respectively.