Studies on synthesis, densification, and characterization of neodymium hexaboride

Abstract Neodymium hexaboride (NdB ₆ ) is an important rare‐earth hexaboride material that has many structural and functional applications in advanced technologies. This paper presents the results on experimental studies of synthesis, densification, microstructural characterization, and mechanical properties of NdB ₆ . Single‐phase NdB ₆ powder was obtained by the carbothermic reduction of Nd ₂ O ₃ and B ₄ C at optimized conditions and charge composition. Densification of NdB ₆ powders was carried out by pressureless sintering and hot pressing. The highest density of 93% theoretical density (TD) was obtained at 1800°C by hot pressing for 2 h in a vacuum, whereas 79% TD was obtained by pressureless sintering at 1900°C. However, 99.9% dense NdB ₆ was obtained by adding a sintering aid of 5 wt.% B ₄ C using a hot‐pressing technique at 1800°C. Microstructural characterization revealed no significant grain growth during hot pressing at 1800°C, and a dominant transgranular mode of fracture was observed in fractography. Hardness values were measured as 23.8 and 28.8 GPa, respectively, by two different techniques micro‐ and nanohardness testers. Fracture toughness and elastic modulus of hot‐pressed NdB ₆ sample were measured as 3.04 MPa m ^1/2 and 484 GPa, respectively. The flexural strength of dense NdB ₆ was obtained as 156 MPa by three‐point bend test.