Microstructures and properties of the tungsten wire/particle reinforced Zr 57 Nb 5 Al 10 Cu 15.4 Ni 12.6 metallic glass
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Microstructures and properties of the tungsten wire/particle reinforced Zr57Nb5Al10Cu15.4Ni12.6 metallic glass composites Haein Choi-Yim, Jan Schroers, and William L. Johnson W.M. Keck Laboratory of Engineering Materials, Mail Code 138-78, California Institute of Technology, Pasadena, California 91125, USA ABSTRACT Tungsten wire or particle reinforced metallic glass matrix composites are produced by infiltrating liquid Zr57Nb5Al10Cu15.4Ni12.6 (Vit106) into tungsten reinforcements at 1150 K and at 1425 K. X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy are carried out to characterize the composite. The matrix of the composite processed at 1150 K is mostly amorphous, with some embedded crystals. During processing, tungsten dissolves in the glass-forming melt and upon quenching precipitates over a relatively narrow zone near the interface between the tungsten and matrix. In the composites processed at 1425 K, tungsten dissolves in the melt and diffuses through the liquid medium, and then reprecipitates upon quenching. The faster kinetics at this high temperature results uniform distribution of the crystals throughout the matrix. Mechanical properties of the differently processed composites containing wires and particles are compared and discussed. The composites exhibit a plasticity of up to 16 % without sacrificing the high strength to failure that is comparable to monolithic Vit 106. INTRODUCTION The limited plasticity of monolithic bulk metallic glasses (BMG’s) has triggered research on metallic glass matrix composites. To improve the toughness two different approaches have been followed. One is to introduce foreign particles into the matrix. It was found that a variety of reinforcement materials such as SiC, WC, Ta, or W can be introduced into the metallic glass matrix without inducing crystallization [1-6]. The size of these particles ranges from 3 µm to 100 µm. One crucial contribution to improve the ductility is the formation of a strong interface between reinforcement material and BMG [7]. To guarantee a strong interface another approach has been followed where the composite forms in-situ. This is done by partially crystallizing the sample upon cooling [8] or upon subsequent heating [9]. The size of these reinforcement crystals varies between several nm to 20 µm. Volume fraction of the reinforcement crystals can be controlled by varying composition, processing time, and temperature, though not as directly as in the case of direct addition of particles to the glass forming melt. The Zr57Nb5Al10Cu15.4Ni12.6 glass-forming alloy is one of the best glass forming Zr-based alloys that does not contain Be [10]. In addition, it is very robust against heterogeneous nucleation at surfaces or interfaces. The thermal stability of this alloy with respect to crystallization is not compromised by adding crystalline particles into its molten state [11]. The plastic deformation range under compression of the glass was improved by 300% when WC, W, or Ta particles with only 5 to 10%
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