Study on Micro-Forming Workability of Thermoplastic Mg-Based Bulk Metallic Glasses

• Main Authors: Tsung-Tien Wu, 吳宗典
• Other Authors: Cheng-Tang Pan
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/85511804780022160861

博士 === 國立中山大學 === 機械與機電工程學系研究所 === 98 === Advancements in technologies such as microelectromechanical systems (MEMS), display devices, biomedical products have created an increasing requirement for miniature components on the scale of micrometers to nanometers. Currently, a commonly used fabrication for miniaturization is LIGA (Lithographie, Galvanoformung, and Abformung). It is a reliably manufacturing method for high-aspect-ratio microstructures with a precision of less than one micrometer. The use of electroplating within LIGA techniques, however, limits the range of materials that can be used. But the main disadvantage of LIGA is its cost: high-energy X-rays generated by synchrotron equipment. The homogeneous and isotropic characteristics of amorphous bulk metallic glasses (BMGs) due to the absence of crystallites, grain boundaries and dislocations lead to the scale of the metallic-glass structures can be miniaturized down to the atomic scale, which presents very high strength, hardness, elastic strain limit and corrosion resistance. In addition, the excellent workability and surface printability in the supercooled liquid state (the region defined from the glass transition temperature (Tg) to the crystallization temperature (Tx) of BMG) has been considered to be one of the most attractive properties of BMGs. The lighter Mg-based metallic glasses exhibit their superior glass forming ability (GFA). Consequently, the using of Mg-based BMGs can gain the goals of light devices and simplify manufacturing process. In this study, therefore, besides the study of LIGA process, a new process utilize the thermoplastic properties of BMGs is presented. First, UV (ultraviolet) -LIGA, a more economical process than LIGA, is used to fabricate the master mold with nickle-cobalt (Ni-Co) alloy. Then, this mold is applied to hot emboss on Mg58Cu31Y11 amorphous alloy to form a secondary mold. The hot embossing temperature is set at 423 K (150 oC) according to the Tg of the BMG around 413 K (140 oC). This embossing process shows that the thermoplastic forming ability of the BMG material is better than Polymethylmethacrylate (PMMA) which requires high hot embossing pressure. BMG is not only a good material for hot embossing process to fabricate microstructure directly, but also a fast-forming material for mold (or die) fabrication. On the other hand, other replicated-able moulds are presented to demonstrate the multifunctional ability of BMGs. First, a mold of oxygen free copper (OFC) with a very low hardness of 1.606 GPa, which is a popular material for machining due to its good machinability, is used to hot emboss on Mg58Cu31Y11 BMG with a higher hardness of 3.445 GPa. Second, micro triangular-pyramidal array (MTPA) on a tungsten (W) steel mold is transferred on Mg58Cu31Y11 BMG using this modified multi-step hot-embossing method to reduce the pattern size. In addition, scratch test with the Nano Indenter® XP system is used to study the mechanical behavior of the Mg58Cu31Y11 BMG for the application such as surface printability.