Structure, Annealing Characteristics and Mechanical Properties of Mg 60 Cu 30-y Y 10 Si y Bulk Amorphous Alloys
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CC11.14.1
Structure, Annealing Characteristics and Mechanical Properties of Mg60Cu30-yY10Siy Bulk Amorphous Alloys U. Wolff, B. Yang1, N. Pryds and J.A.Wert Materials Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark 1 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
ABSTRACT
The effect of different Si contents on the glass forming ability (GFA) and the amorphous-tocrystalline transformation has been investigated for the Mg-Cu-Y-Si system. Four Mg60Cu30-yY10Siy (y = 1-5 at.%) alloys were prepared using a relatively simple technique of rapid cooling of the melt in a copper mould. Crystallization was induced by heat treatment of the alloys and the samples were then characterized concerning their microstructure and thermal stability by X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) at a constant heating rate. Partial substitution of Cu by Si leads to a transition of the as-cast structure at a constant cooling rate from amorphous to crystalline with increasing Si content. Furthermore, the glass transition temperature (Tg) of the Mg-Cu-Y-Si alloy is lower compared to the Mg-Cu-Y system. The mechanical properties of the bulk Mg-Cu-Y-Si alloys have been investigated and found to vary with the Si content.
INTRODUCTION
Among a large number of amorphous alloys, those based on Mg have attracted attention due to a high strength-to-weight ratio. Recently, based on the Mg-Cu-Y ternary system, quaternary Mg-Cu-Ag-Y [1], Mg-Cu-Zn-Y [2], Mg-Cu-Y-Al [3-5] and Mg-Cu-Y-Li [6,7] alloys have been developed. Apparently, increasing the multicomponent interaction in alloys is an important route to develop new easy glass forming materials [8,9]. The overall aim of the present work is to study a new Mg-based alloy system, which exhibits both high strength-to-weight ratio and a low glass transition temperature. In the present work, the element Cu in the Mg60Cu30Y10 alloy is partially substituted with Si to form a quaternary Mg60Cu30-yY10Siy (y = 1.0, 1.8, 2.5 and 5.0 at.%) alloy. Si was selected as a candidate element for the following reasons: (1) a large difference in atomic size between Si and the constituent elements. The Goldschmidt atomic radius of Si is 1.17 Å, which is significantly less than 1.60, 1.28 and 1.80 Å for Mg, Cu and Y, respectively [10]; (2) large mixing enthalpies between Si-Mg and Si-Y. According to Inoue et al. [8], larger atomic size ratios and a larger negative enthalphy of mixing between the constituent elements together with the difficulty of redistribution of these elements for crystallization are important for the increase in GFA and the appearance of a wide supercooled liquid interval.
CC11.14.2
We have studied the effect of Si as a substituting element for Cu on the GFA of Mg60Cu30-yY10Siy alloys. The GFA is increased at y = 1.0 at% compared to the Si free alloy and also the hardness of these alloys is enhanced. Along with the microstr
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