Formation of 3-Dimensionally Orientated Nano-sized Crystals in an Amorphous Alloy under Ion Beam Irradiation
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Formation of 3-Dimensionally Orientated Nano-sized Crystals in an Amorphous Alloy under Ion Beam Irradiation Takuya Kamikawa, Ryuichi Tarumi, Kazuki Takashima and Yakichi Higo Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan ABSTRACT We have succeeded to form three-dimensionally orientated nano-sized crystals in a Ni-P amorphous alloy under focused ion beam (FIB) irradiation. The FIB micro-fabrication was performed on an electroless deposited Ni-P amorphous alloy and thin films with a thickness of 100 nm were prepared. Transmission electron microscopy (TEM) observation for irradiated areas revealed the formation of crystallographically orientated nano-sized crystals (NCs) in the irradiated region. The grain size of NCs was less than 10 nm in diameter. Electron diffraction analysis showed that the formed NCs have a face-centered-cubic (f.c.c.) structure and the following orientation relationships among the specimen, the NCs and the FIB direction: irradiated plane // {111}f.c.c. and ion beam direction // f.c.c.. INTRODUCTION Nano-sized crystals (NCs) have been expected to be more widely applied to many industrial fields. Over the past decade, many studies have been achieved to form NCs, since NCs have a potential to improve mechanical or magnetic properties of materials [1, 2]. To date, several methods, deposition on substrates, recrystallization following severe plastic deformation, precipitation of a secondary phase, and crystallization from a amorphous state, have been proposed to form NCs. It is, however, difficult to obtain crystallographically orientated NCs while controlling their size less than 10 nm diameter. Ion beam irradiation is one of the attractive methods to control the structure of materials in the order of nanometers. Several kinds of structural changes, precipitation of implanted ions [3], formation of dislocation loops [4], phase transformation from crystalline to amorphous structure [5], and vice versa [6], have been reported under ion beam irradiation. Amorphous alloys are in a nonequilibrium thermal state so that a phase transformation from amorphous into crystalline structure can be expected under ion beam irradiation, but the details have not been identified. In this study, we have investigated the structural changes of a Ni-P amorphous alloy
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under focused ion beam (FIB) irradiation by using transmission electron microscopy (TEM). EXPERIMENTAL DETAILS In this investigation, a Ni-11.5 wt% P amorphous alloy prepared by electroless deposition on an Al-Mg alloy substrate was employed (Fig. 1 (a)). The thickness of the amorphous alloy layer was 12 Lm. The amorphous layer was separated from the Al-Mg alloy substrate using a NaOH aqueous solution (Fig. 1 (b)). Specimens were then heat treated at 473 K for 30 minutes. The amorphous layer was mechanically cut into a circular disk with a diameter of 3 mm (Fig. 1 (c)). Electrical polishing was performed in a HCl-CHCOOH (9:1) mixed solution at 273 K to reduce
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