Formation of Nano-Sized Crystals During Plastic Deformation in Amorphous Alloys
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Formation of Nano-Sized Crystals During Plastic Deformation in Amorphous Alloys
A. Ogura, M. Sato, R. Tarumi, M. Shimojo, K. Takashima and Y. Higo Precision and Intelligence Laboratory, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan [email protected]
ABSTRACT Microstructural change in deformation bands was observed in a Ni-P amorphous alloy using transmission electron microscopy (TEM). Bending strain was applied to a micro-sized cantilever beam specimen. A TEM specimen was prepared from the micro-sized specimen with keeping the information on the relationship between the deformed direction and the specimen orientation. TEM observation in deformation bands revealed that plastic deformation induces the precipitation of nanocrystalline Ni particles. An orientation relationship between deformation direction and crystal orientation was obtained, that is, a (111) plane of all crystalline particles are parallel to the side surface of the specimen. KEYWORDS: nano structure, amorphous alloy, plastic deformation, crystallization, TEM observation
INTRODUCTION Micromachines and micro electro mechanical system (MEMS) devices are expected to be applied more widely in many fields in the near future. The devices are used not limited in biomedical fields, but in automobiles, home appliances, computers and telecommunication fields. Application examples include accelerometers, pressure sensors, flow detectors, disc drives, and so on. The size of some components used in these devices is considered to be in the order of microns. The mechanical properties of such materials may be different from those of bulk materials due to the size effects such as the effects of crystal grain size. Amorphous alloys are potential candidate materials for future micromachines and MEMS because of their isotropic mechanical properties, high strength and uniform structure [1]. In addition, amorphous alloys can be formed on substrates by sputtering and depositing techniques. Then, surface integrated micromachines can be constructed on the substrate material. However, the elongation of amorphous alloys is low accompanied with localized deformation at room temperature [2]. Strengthening methods for such micro-sized components are considered to be indispensable using nano-structural control techniques. The materials which contain nano-sized crystals in amorphous matrix may have improved deformation behavior. Such nanocrystalline amorphous alloys can be produced by two different methods. One method is a heat treatment on amorphous alloys (thermal crystallization). A partially crystalline material with crystal sizes ranging from 2 to 15nm was obtained by annealing a Ni based amorphous alloy for 2 months at a temperature well below the crystallization temperature [3]. The other is a plastic deformation process (mechanical crystallization). It has been reported that Fe and B1.10.1
Al based amorphous alloys, which have been deformed by high-energy ball milling, have nano-sized crystals in amorphous matrices [4-6]. In t
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