Mechanical properties of bulk metallic glasses and composites
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S. Pauly IFW Dresden, Institut für Komplexe Materialien, Postfach 270116, D-01171 Dresden, Germany; and FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, D-64287 Darmstadt, Germany
C. Duhamel FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, D-64287 Darmstadt, Germany; and IFW Dresden, Institut für Komplexe Materialien, Postfach 270116, D-01171 Dresden, Germany (Received 17 August 2006; accepted 23 October 2006)
The development of bulk metallic glasses and composites for improving the mechanical properties has occurred with the discovery of many ductile metallic glasses and glass matrix composites with second phase dispersions with different length scales. This article reviews the processing, microstructure development, and resulting mechanical properties of Zr-, Ti-, Cu-, Mg-, Fe-, and Ni-based glassy alloys and also considers the superiority of composite materials containing different phases for enhancing the strength, ductility, and toughness, even leading to a “work-hardening-like” behavior. The morphology, shape, and length scale of the second phase dispersions are crucial for the delocalization of shear bands. The article concludes with some comments regarding future directions of the investigations of spatially inhomogeneous metallic glasses.
I. INTRODUCTION
The first amorphous metal was prepared in 1934 using an evaporation method.1 Later on, the synthesis of amorphous alloys was also reported by electrodeposition in 19502–4 and by splat quenching of Au–Si alloys in the 1960s.5 After that, (bulk) glass formation in Pd-based,6–8 Al-based,9 Mg-based,10 and Zr-based11,12 alloys was reported. Even though the mechanical strength of metallic glasses was found in the 1970s and 1980s13–15 to be superior to that of microcrystalline alloys, at this time the small specimen size restricted conventional mechanical characterization. This was realized only after the production of bulk Zr-based metallic glasses (BMGs).11,12 The major advantage of metallic glasses is their high elastic strain (∼2%), which is much higher than that of common crystalline metallic alloys (1 mm).9,11 BMG composites can also be prepared by these procedures, i.e., through (i) mechanical alloying and consolidation,35 (ii) solidification,11,12 or (iii) partial devitrification of amorphous precursors by either thermal treatment36–38 or severe plastic deformation/high pressure torsion.39,40 The various processing routes and the evolution of BMG composites with different length scales of second phases are schematically described in Fig. 1.
groups: ex situ and in situ formed composites. The microstructural features of these composites can exhibit different features and length scales of second-phase constituents, as exemplified in Fig. 1. The ex situ composites are formed in two ways. The first is mechanical alloying of powders or atomization41,42 containing a glassy phase and reinforcing second-phase particles, for example, by mixing immiscible
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