Evaluation of Mo-based Amorphous Alloy Thin Films Exhibiting High Crystallization Temperature

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0894-LL03-07.1

Evaluation of Mo-based Amorphous Alloy Thin Films Exhibiting High Crystallization Temperature Junpei Sakurai1, Seiichi Hata2, Ryusuke Yamauchi1 and Akira Shimokohbe1 1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama, Japan. 2 Frontier Collaborative Research Center, Tokyo Institute of Technology ABSTRACT This paper presents the characteristics of Mo-based (Mo-Zr based) amorphous alloys exhibiting a high crystallization temperature. In order to investigate the alloy composition showing an amorphous state in the Mo-Zr-X (X=Si and Al) alloy system, thin film libraries were prepared at first by combinatorial arc plasma deposition (CAPD). The composition region corresponding to the amorphous state was identified in the libraries with X-ray diffraction. On the basis of the alloy composition and phase distribution of the thin film libraries, additional amorphous Mo-Zr-Si and Mo-Zr-Al thin films were prepared by a carousel sputtering system. The crystallization temperature Tc of the amorphous Mo50Zr(50-x)Six thin films exceeded 1073 K. However, the Mo-Zr-Si thin films were so brittle that they could not be subjected to tensile testing. In the Mo-Zr-Al thin films, Tc of the Mo-rich MoxZr(90-x)Al10 and MoxZr(76-x)Al24 thin films exceeded 973 K. Although the toughness of Mo-based amorphous alloy thin films could be improved slightly by adding Al, the amorphous Mo-Zr-Al thin films were also brittle. INTRODUCTION Recently, the Blu-ray Disc (BD) application has expanded rapidly. BD enables largecapacity storage by using a blue-violet laser for writing/reading. The pick-up lens for BD requires high heat resistance and multi-wavelength capability (interchangeable with CD/DVD by using a red laser). At present, optical plastic and glass lenses are employed for many CD/DVD products. However, plastic lenses are not suitable for BD because they cannot withstand the heat. Therefore, the development of an ultra-high-precision optical glass lens for BD is needed. The optical glass lenses for CD/DVD products are mainly produced by injection molding using hard material molds. But hard materials, such as tungsten carbide, are too hard to be ultra-high-precision-worked, such as by diffraction grating. Thus, we took notice of the amorphous alloys that are widely used for injection molding of plastic lenses. An amorphous alloy, such as electro-less plated Ni-P alloy, shows superior machinability and can be ultra-highprecision-worked. However, since Ni-P alloy reacts to glass melting, it is not suitable for glass molding. Thus, amorphous alloys are expected to be used as molds of optical glass lenses. Materials for glass molding need to be stable at high temperatures (around 873 K). Therefore, amorphous alloys exhibiting a high crystallization temperature (over 973 K) need to be developed. In order to increase the crystallization temperature of amorphous alloys, their melting point needs to rise. Mo-Zr alloys are expected to exhibit a high crystallization temperature [1]. Mor