Competition between densification and microstructure development during spark plasma sintering of B₄C–Eu₂O₃

The densification of nonoxide ceramics has been a known challenge in the field of engineering ceramics. The amount and type of sinter-aid together with sintering conditions significantly influence the densification behavior and microstructure in nonoxide ceramics. In this perspective, the present work reports the use of Eu₂O₃ sinter-aid and spark plasma sintering towards the densification of B₄C. The densification is largely influenced by the solid-state sintering reactions during heating to 1900°C. Based on the careful analysis of the heat-treated powder mixture (B₄C–Eu₂O₃) and sintered compacts, the competitive reaction pathways are proposed to rationalize the formation of EuB₆ as dominant microstructural phase. An array of distinctive morphological features, including intragranular and intergranular EuB₆ phase as well as characteristic defect structures (asymmetric twins, stacking faults and threaded dislocations) are observed within dense B₄C matrix. An attempt has been made to explain the competition between microstructure development and densification.