Centimeter-scale-diameter Co-based bulk metallic glasses with fracture strength exceeding 5000 MPa

Co_48-xFe_xCr₁₅Mo₁₄C₁₅B₆Er₂ (x = 2.5 and 5) bulk metallic glasses (BMGs) with critical size (d_c) up to 15 mm in diameter were synthesized by copper mold casting. Co₄₃Fe₅Cr₁₅Mo₁₄C₁₅B₆Er₂ BMG has a wide supercooled liquid region (84 K) and ultrahigh fracture strength exceeding 5000 MPa, which is the highest value for reported metallic glasses with d_c exceeding 1 cm. Furthermore, the Poisson ratio, Young modulus, shear modulus and bulk modulus of this alloy were evaluated to be 0.31, 217 GPa, 82 GPa and 214 GPa, respectively. The ideal configurational entropy of Co_48-xFe_xCr₁₅Mo₁₄C₁₅B₆Er₂ (x = 0 and 5) has been calculated. The introduction of the similar element Fe in the Fe-free Co-Cr-Mo-C-B-Er alloy will be beneficial to increasing the ideal configurational entropy and depressing the critical cooling rate to achieve greater glass-forming ability. The combination of superior glass-forming ability and ultrahigh fracture strength makes the present Co_48-xFe_xCr₁₅Mo₁₄C₁₅B₆Er₂ (x = 2.5 and 5) BMGs promising candidates as advanced structural materials.