Combinatorial Searching for Noble Metal-based Thin Film Amorphous Alloys for Glass Lens Mold
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Combinatorial Searching for Noble Metal-based Thin Film Amorphous Alloys for Glass Lens Mold Junpei Sakurai1, Seiichi Hata2, Ryusuke Yamauchi1, Hiroyuki Tachikawa1, and Akira Shimokohbe1 1 Precision and intelligence Laboratory, Tokyo Institute of Technology, R2-37, 4259 Nagatsuta, Midoriku, Yokohama, 226-8503, Japan 2 Frontier Collaborative Research Center, Tokyo Institute of Technology, S2-8, 4259 Nagatsuta, Midoriku, Yokohama, 226-8503, Japan ABSTRACT This paper presents the properties of Pt-based thin film amorphous alloys developed for a glass lens mold. To search for the amorphous alloys, Pt-Zr-Ni and Pt-Hf-Ni thin film libraries were fabricated using combinatorial arc plasma deposition (CAPD). The composition ranges of the amorphous region in each library were 50 to 60 at.% Pt, 0 to 20 at.% Ni, and balance being Zr or Hf. To evaluate the thermal and mechanical properties of these amorphous alloys, Pt51Zr39Ni10 and Pt52Hf36Ni12 samples, as typical amorphous samples, were prepared by sputtering. The Pt51Zr39Ni10 sample showed a crystallization temperature, Tx, of 939 K and a fracture stress, σf, of 1.44 GPa. The Pt52Hf36Ni12 sample showed a Tx of 978 K and a σf of 0.3 GPa. The Pt51Zr39Ni10 and Pt52Hf36Ni12 samples did not achieve the target Tx (973K) and σf (1.0 GPa). In order to achieve the target properties, Zr was displaced with Hf to increase the Tx of PtZr-Ni and four Pt51HfxZr37-xNi12 samples were prepared. The Pt51Hf20Zr17Ni12 sample had a Tx of 992 K and a σf of 0.87 GPa, and almost achieved the target properties. The machinability of the Pt51Hf20Zr17Ni12 sample was also evaluated. Though this sample could be cut using a diamond tool, it did not show sufficient machinability. In order to improve the accuracy of the glass mold shape, the machinability of the Pt-based thin film amorphous alloys require further modification.
INTRODUCTION Recently, functional optical glass lenses, such as a pick-up lens with a diffraction grating and a high precision lens, have been under development. In order to realize these glass lenses, molds with a precise structure such as a diffraction grating are needed. Conventional glass lenses are produced using molds made of hard materials, such as WC, and these molds are cut using diamond tools. However, these materials are too hard for high-precision work such as a diffraction grating, and it is very difficult to form molds for functional optical glass lenses using these materials. Hence, functional optical lenses have not been developed thus far. In this paper, we attempted to search for Pt-Zr and Pt-Hf based amorphous alloys as new materials for glass lens molds. Generally, since Pt and Pt-based alloys have good oxidation resistance, they are expected to be suitable for glass lens molds that can be used under high temperatures. However, in order to use these amorphous alloys for glass lens molds, they need to have a high crystallization temperature, Tx, which is higher than the molding temperature. Figure 1 shows the phase diagram of the Pt-Zr binary system [1].
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