| Abstract Scope |
Lower damage tolerance of (Hf,Zr)B2 based refractory ceramics restrict them to be used for re-entry conditions. B4C as sintering additive helps in improving the damage tolerance by enhancing the densification. Herein novel equimolar HfB2/ZrB2 composite with 6 vol% B4C reinforcement are spark plasma sintered at 18500C and 30 MPa pressure. Densification increases from 90% for HfB2¬-ZrB2 to 99% with B4C addition. Due to B4C addition, hardness and elastic modulus increases from 25 GPa to 38 GPa (+52%) and 465 GPa to 868 GPa (+87%), respectively. During sintering, compressive residual stresses get generated within the matrix due to CTE mismatch between HfB2, ZrB2 and, B4C. These residual stresses along with densification and solid solution formation, deflects the crack, and thus increases fracture toughness (from 2.6 MPa.m0.5 to 3.7 MPa.m0.5) of the composite. Further, tribological damage is also assessed for (Hf,Zr)B2 composites reinforced with B4C. |