| dc.description.abstract | Owing to the unique and excellent properties of bulk metallic glass (BMG), it has become hot-spot and attracted lots of countries to develop it actively in recent year. However, the disadvantage of metallic glass is lack of ductility, which limits the range of application. Therefore, many studies use the concept of composite materials, by using the in-situ or ex-situ approach to generate the second phase in metallic glass matrix to restrict the shear band propagation and so as to improve the plasticity of BMGC.
In this research, we use four different processes, tilt-casting, suction-casting, injection-casting, and directly quenching to make the different size (2~4mm) of Zr48Cu47.5Al4Co0.5 and Zr47.5Cu47.5Al5 BMGC rods. Using the four different processes to observe the distribution of holes and in-situ ZrCu B2 phase. The size and distribution of B2 phase and porosity were examined by optical microscopy as well as scanning electron microscopy. Then the mechanical properties of these BMGC rods were obtained by uniaxial compression test. In addition, the Reynolds number of each process was also estimated to figure out the formation of B2 second phase, and relate to its mechanical performance.
After uniaxial compression testing, the 2mm diameter BMGC rods made from each casting process have the better plasticity than the other diameter samples. Among all the 2mm-diameter samples, the tilt casting 2mm-diameter Zr48Cu47.5Al4Co0.5 sample present the best mechanical performance, it can reach 16% plastic deformation. Through the calculation of Reynolds number, tilt-casting has lower value of Reynolds number and the fluid flow mode close to the laminar flow. Therefore, this more stable melt flow makes the formation of ZrCu B2 phase to form a larger size and more homogeneous distribution in the amorphous matrix.
In this research also use ultrasonic testing to discuss the mechanical properties of metallic glass composite rods, such as Poisson’s ratio, shear modulus and bulk modulus etc. Among the rods by tilt casting have much better mechanical performances because of much lower defects in the rods.
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