Abstract:Lanthanum hexaboride (LaB6) is an excellent high-temperature ceramic material for thermionic cathodes. However, the high brittleness of LaB6 makes it difficult to process, limiting the further engineering application. In this study, Barium hexaboride (BaB6) with low work function and Vanadium diboride (VB2) with high elastic modulus were added into LaB6. (La0.5Ba0.5)B6-VB2 composite with the high relative density of 98.57%, whose matrix is a single-phase solid solution, was prepared by spark plasma sintering (SPS) under the conditions of 1900 ℃, 40 MPa, and 5 min. As the sintering temperature increases from 1500 ℃ to 1900 ℃, the average grain size of the composite increases from 2.68±1.44 μm to 7.21±1.37 μm, Vickers hardness increases from 16.57±0.88 GPa to 24.89±1.26 GPa, fracture toughness increases from 1.95±0.16 MPa·m1/2 to 3.81±0.28 MPa·m1/2, and the maximum bending strength reaches 376.32 MPa. Crack deflection and branching are identified as the primary toughening mechanisms in the composite. (La0.5Ba0.5)B6-VB2 composite exhibits the maximum current density of 7.56 A/cm2 and the minimum work function of 2.97 eV.