Unveiling the Synergistic Mechanism of Hardness and Toughness Enhancement in HPHT-Synthesized WAlB

Abstract Balancing hardness and toughness in ceramics to ensure reliable performance under extreme conditions remains a central and actively pursued research challenge. Recently, layered boride MAB phases have attracted increasing attention due to their excellent combination of metallic and ceramic properties. Their unique crystal structure and superior mechanical properties position them as promising candidates for high-toughness ceramics. Herein, WAlB, a typical MAB phase, was synthesized using a high pressure and high temperature method at 5 GPa and 1500 K. The synthesized WAlB sample exhibits excellent mechanical properties, with a Vickers hardness of 15.9 GPa, a fracture toughness of 6.2 MPa·m1/2, and a Young’s modulus of 377.5 GPa. First-principles calculations combined with experimental characterization confirm that the high hardness of WAlB originates from a robust internal B–B covalent bond framework, along with its high elastic and shear moduli. Additionally, its submicron lamellar grain structure and high grain boundary density contribute to further hardness enhancement, as described by the Hall-Petch effect. The exceptional fracture toughness arises from intrinsically anisotropic bonding characteristics, directionally preferred metallic bonds, and abundant microstructural defects that facilitate crack energy dissipation. This work establishes an experimental foundation and yields practical design principles for advancing high-toughness ceramics from synthesis to application.