New compositional design for creating tough metallic glass composites with excellent work hardening

The extrinsic size of both crystalline alloys and amorphous metallic alloys strongly affects their mechanical properties at the submicron scale or nanometre scale. For example, Zr-based metallic glass nanopillars exhibit ceramic-like strengths (2.25 GPa) and metal-like ductility (25%) simultaneously when the pillar dimension is reduced to <100 nm. Here, we report a new compositional design approach to create tough metallic glass composites consisting of micrometre-scale dendrites and nanometre-scale amorphous matrices that exhibit high strength and ductility in the normally brittle MgZnCa metallic glass system. When the thickness of the amorphous matrix is reduced to the nanometre scale, a low density (p approximate to 1.99 g cm(-3)) Mg91.5Zn7.5Ca1 alloy exhibits room temperature tensile ductility exceeding 15.6%, a yield strength of 215 MPa and a fracture strength of 478 MPa. Transmission electron microscopy analysis demonstrates that the alloy consists of micrometre-scale alpha-Mg solid solution dendrites and nanometre-scale amorphous matrix (80-530 nm in thickness). The homogeneous deformation of nanometre scale amorphous matrices is believed to be responsible for the high toughness and excellent work-hardening behaviour. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.