Effects of LaB6 content on microstructure and mechanical properties of TaC-LaB6 composites

Tantalum carbide (TaC)-based composites containing 0.1-30 mol% lanthanum hexaboride (LaB6) were prepared by hot pressing at 1900 °C for 30 min under 30 MPa pressure. Effects of LaB6 content on densification, microstructure and mechanical properties of the consolidated TaC-LaB6 composites were investigated. Sinter-forge was performed to test creep resistance of the TaC-LaB6 composites at temperatures up to 1950 °C. Addition of LaB6 increased densification of the TaC-LaB6 composites and the compositions with ≥1 mol% LaB6 almost reached full densities. LaB6 reacted with TaC and the Ta2O3 impurity to form minor phases of TaB2, B2O3 and C. Average size of the TaC grains in the consolidated composites showed a decrease trend with increase in the LaB6 content. The TaC-LaB6 composites with 1-2 mol% LaB6 addition had relatively good flexural strength, Vickers hardness and fracture toughness with a value of 530 MPa, 15.6 GPa and 5.29 MPa m1/2, respectively. Addition of LaB6 modified interfacial bonding strength of the TaC grains, hence increase in creep resistance under sinter-forge up to 1950 °C.