| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士班 === 99 === With the superior properties of high strength, high elastic strain limit, relatively low Young’s modulus, excellent corrosion resistance and wear resistance, Zr-based bulk metallic glasses (BMGs) showed a promising potential in the biomedical applications and have attracted much attention in recent years. However, most of the Zr-based BMGs contained the element Ni, which is usually blamed for the occurrence of allergy and is possibly carcinogenic to the human body. It seriously limited the biocompatible applications of Zr-based BMGs.
In recent years, it indicated that the adding of Nb is believed to be efficient to improve the plasticity and the corrosion resistance of Zr-based BMGs. Meanwhile, it is also believed that the addition of Pd is effective to enhance the thermal properties of Zr-based BMGs. Therefore, the Zr53Cu30Ni9Al8 BMG with high glass forming ability (GFA) is selected as the base alloy in this research. Pure elements Pd and Nb are used in place of Ni in the base alloy. The tests of the thermal properties and the mechanical properties, and the microstructure observation of the Ni-free Zr-based BMGs with the adding of Pd and Nb are followed.
It revealed that GFA andΔTx of the Zr53Cu30Nb4.5Pd4.5Al8 alloy is better than that of the based alloy. The result of mechanical properties tests shows that the yield strength of Zr53Cu30NbxPd9-xAl8 BMGs significantly increaseed in the range of 1700 MPa to 1900 MPa. Moreover, a remarkable compression plastic strain (11.2%) of Zr53Cu30Nb4.5Pd4.5Al8 BMG rod with 2mm in diameter was observed. In addition, TEM observation revealed that a nanocrystalline phase co-existing in the amorphous matrix of the as-cast Zr53Cu30Nb4.5Pd4.5Al8 alloy. The nano-crystalline phase (with size of about 5-20 nm) embedded uniformly in the amorphous matrix of the Zr53Cu30Nb4.5Pd4.5Al8 alloy and it was identified to be the tetragonal structured NbPd3 phase. The homogeneous dispersed nano-crystalline phase resulted in the formation of multiple shear bands. It decreased the propagation of shear bands and so as to significantly improve their plasticity.
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