Mg-based bulk metallic glass composites with plasticity and gigapascal strength

The lightweight Mg₆₅Cu_7.5Ni_7.5Zn ₅Ag₅Y₁₀ bulk metallic glasses (BMG) always fail before yielding, with irreproducible strengths <650 MPa. Adding particles of TiB₂ as the reinforcing phase, which can be uniformly distributed in the matrix without adversely affecting its glass-forming ability upon copper mold casting, the BMG composites can sustain a plastic strain to failure of 2-3% at a compressive fracture strength as high as 1.3 GPa. The strengthening/ toughening effects of the second phase particles are attributed to their ability to serve as obstacles to the propagation of run-away shear bands and micro-cracks, as well as to the generation of multiple shear bands due to the large elastic mismatch between the TiB₂ and the matrix. The angle between the compressive shear plane and loading axis is ∼41°, consistent with the Mohr-Coulomb criterion. The very high specific strength of ∼3.5 × 10⁵ N m kg^-1 exceeds by far those of commercial Mg or Al alloys and even Zr-based BMGs.