Theoretical prediction, preparation, and mechanical properties of YbB₆, a candidate interphase material for future UHTC_f/UHTC composites

High melting point, low shear deformation resistance and high volume expansion upon oxidation are the basic requirements for interphase materials of future ultrahigh-temperature ceramic fiber reinforced ultrahigh-temperature ceramic matrix (UHTC_f/UHTC) composites. YbB₆ is one of the materials that possesses a combination of these properties. In this work, using a combination of first-principles calculations based on density functional theory and experimental investigations, low shear deformation resistance of YbB₆ (theoretically predicted 81 GPa, experimentally determined 80 GPa) is confirmed. In addition, YbB₆ has low Pugh's ratio G/B, low brittleness index M = H_v/K_IC, but high damage tolerant index D_t=K_IC×E/σ_b×H_v, which endow that cracks are arrested or deflected when propagated from the matrix if it was used as an interphase material for UHTC_f/UHTC composites. Details on the preparation, structural features and mechanical properties (hardness, strength, fracture toughness) of YbB₆ are also given.