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

The lightweight Mg65Cu7.5Ni7.5Zn5Ag5Y10 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.