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angyin Yuana) National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200240, China; and State Key Laboratory of Metallic Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, China

Zhenhua Chu and Jian Zhang National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200240, China

Wenjiang Ding National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200240, China; and State Key Laboratory of Metallic Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, China (Received 21 May 2009; accepted 1 September 2009)

Based on a ternary Mg75Ni15Gd10 metallic glass former, a new Mg80Ni12Gd4Nd4 bulk metallic glass composite (BMGC) was developed by tailoring the compositions of Mg and rare earth (RE) elements. This BMGC displayed compressive ultimate strength over 900 MPa with a total strain to failure of 4.3% and specific strength of 3.12
105 Nm/kg. The improved mechanical properties were attributed to a “dual phases” structure consisting of Mg solid solution flakes and glassy matrix in the Mg80Ni12Gd4Nd4 BMGC. The homogeneously dispersed Mg phases reinforcement in the BMGC were characterized as a long period ordered structure (LPOS) with periodic arrays of six close-packed planes distorted from the ideal hexagonal lattice of 6H-type. The LPOS-Mg in the composite can act as a soft media to trap or interact with the unstable shear bands and contribute to plastic strain. The present study may provide a guideline for designing the Mg–TM–REbased (TM: transition metals) BMGCs with “dual phases” structures. I. INTRODUCTION

Mg-based bulk metallic glasses (BMGs), compared to the conventional Mg-based crystalline alloys, show much higher strength up to over 900 MPa, for which they received special attention. Similar to some of the other BMGs, the lack of enough plasticity for Mg-based BMGs is a challenge for their potential engineering application. To improve the plasticity for Mg-based BMGs, in situ or ex situ bulk metallic glass composites (BMGCs) were designed. The particulates, such as TiB2,1 Nb,2 Ti,3 and Mo,4 were introduced into the Mg-based BMGs, which all favored enhanced plasticity for the corresponding composites. In situ Mg-based BMG composites with Fe5 or Ti6 dispersions with improved plasticity were also fabricated. However, in these composites, the glassy matrix contains a relatively low content of 65 at.% Mg element, which resulted in a much higher density (above 3.5 g/cm3)7 than the density for the Mg-based crystalline a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0438 J. Mater. Res., Vol. 24, No. 12, Dec 2009

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alloys (below 2.0 g/cm3), and consequently harmed the advantage in lightweight for the Mg-based alloys. In contrast, Hui et al.8 reported an in situ Mg81Cu9.3Y4.7Zn5 BMGC with a relatively higher content of Mg (i.e., lower density), which si