Formation, microstructure and properties of long-period order structure reinforced Mg-based bulk metallic glass composites

In situ Mg-Cu-Y-Zn bulk metallic glass (BMG) matrix composites, in which Mg solid solution flakes of 0.5-1 mu m thickness and 2-10 mu m length are dispersed, have been prepared by copper mold casting. The Mg flakes are characterized as a long-period order structure (LOS), i.e. periodic arrays of six close-packed planes distorted from the ideal hexagonal lattice of 6H-type. The formation mechanism of LOS is interpreted as the precipitation of the leading phase of the eutectic reaction above the glass transition temperature. In comparison with monolithic Mg-based BMG alloys, the composites with an LOS exhibit significant improvement in mechanical properties, e.g. a compressive plastic strain of similar to 18% and ultimate strength of similar to 1.2 GPa, have been measured in Mg81Cu9.3Y4.7Zn5 alloy. It is suggested that the enhancement of the mechanical properties of the composites can be attributed to the generation of multiple shear bands and the deformation of the LOS. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.