Fabrication of tantalum monoboride ceramics: Effects of B, SiC, and Si ₃ N ₄ additions

Abstract Synthesis and optimization of tantalum monoboride (TaB) ceramics were investigated to address a gap in the literature where TaB‐based bulk ceramics are underexplored despite their predicted excellent mechanical properties. The main focus was put on evaluating influence of extra boron (0.85–1.5 at%), silicon carbide (3–15 wt%), and silicon nitride (1–15 wt%) additions on densification, phase purity, microstructure, and mechanical performance of the TaB ceramics. In the study, a Ta+B powder mixture for stoichiometric TaB was consolidated via reaction reaction hot pressing (RHP) at 1800°C and 1900°C under 30 MPa for 1 h. Because it yielded poor densification (∼62% relative density) and undesirable impurity phases, various processing routes were tried to obtain the desired TaB ceramic, the methods including (i) using B additive and C (introduced as impurity by wear of milling ball coating) to eliminate the minor oxygen‐related impurities TaC and Ta 2 O, (ii) using SiC/Si 3 N 4 to deoxidize the reaction system and reinforce the TaB composites, and (iii) using RHP versus spark plasma sintering (SPS) to compare effects of sintering temperatures and time. Thermodynamic analysis was done to facilitate understanding phases formation. The results showed that densification was improved by additions of 0.85–1.5 at% extra B in combination with SPS at 2100°C under 40 MPa for 10–30 min, but the minor impurity phase TaC or Ta 2 O remained. Additions of Si 3 N 4 at 3 wt% and above emerged as effective, achieving near‐full density (>97% relative density) and good mechanical properties, with Vickers hardness, flexural strength, and fracture toughness reaching 26.1 ± 1.3 GPa, 705 ± 45 MPa, and 4.40 ± 0.19 MPa·m 1/2 , respectively. Residual oxygen seemed to have been collected in Si 3 N 4 ‐Si 2 N 2 O aggregates due to the formation of minor Si 2 N 2 O, a beneficial situation, leaving clean TaB grain boundaries for possible better mechanical performance of the TaB‐Si 3 N 4 composites at high temperatures. In contrast, SiC addition cannot be recommended because it promoted impurity phases (e.g., TaC, TaSi 2 , Ta 5 B 6 , and Ta 3 B 4 ) and failed to enhance densification (RHP at 1800°C under 30 MPa for 1 h) at low content of SiC additions <5 wt%, while the aimed TaB was completely missed at 5–15 wt% SiC additions.