Effects of P Content on Morphology of Nanocrystals Induced by FIB Irradiation in Ni-P Amorphous Alloy
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0960-N09-08
Effects of P Content on Morphology of Nanocrystals Induced by FIB Irradiation in Ni-P Amorphous Alloy Koji Sato, Chiemi Ishiyama, Masato Sone, and Yakichi Higo Precision and Intelligence Laboratory, Tokyo Institute of Technology, Nagatuta 4259 R2-18, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT We studied the effects of phosphorus (P) on Ni nanocrystalline morphology formed by focused ion beam (FIB) irradiation for Ni-P amorphous alloy thin films. The P content in the amorphous alloy was varied from 8 to 12 wt.%. The nanocrystals induced by the FIB irradiation for Ni-11.8, 8.9, 7.9 wt.％P amorphous alloy had an f.c.c. structure and showed unique crystallographic orientation relationships to the geometry of the focused ion beam, that is, {111}f.c.c. parallel to the irradiated plane and f.c.c. parallel to the projected ion beam direction, respectively. The Ni nanocrystals precipitated like aggregates with decreasing of the P content. These results represent that the P content does not affect crystallographic orientation relationships, while influences the precipitation distribution of Ni nanocrystals generated by the FIB irradiation.
INTRODUCTION Over the past decade, there have been many reports concerning on the fabrication method of nano-sized crystals. Nanocrystalline materials have been employed for wide scientific areas because of their excellent functional properties, for example, physical, chemical, and mechanical properties as a consequence of their high density of interfaces, compared with conventional coarse-grained materials [1,2]. Nanocrystalline materials, therefore, provide attractive potential for a variety of technological applications. Irradiation of high-energy particles such as ion, electron and neutron has been one of the attractive methods to control the structure of materials with the sizes of the order of nanometers. Recent studies reported several kinds of structural changes under such high-energy particle irradiation; precipitation of implanted ions [3], formation of dislocation loops [4], phase transformation from crystalline to amorphous structure [5], and vice versa [6]. Specifically, amorphous alloys are in a thermally nonequilibrium state. Therefore, phase transformation from amorphous into crystalline structure can be expected by ion beam irradiation. However, the details of this mechanism have not been clarified yet. In previous works, we have reported the formation of crystallographically oriented Ni nanocrystals, with the size of 5 ~ 10 nm, as a result of the focused ion beam (FIB) irradiation for a Ni-11.5wt.%P amorphous alloy, which was annealed at 473 K for 0.5 hour prior to the irradiation [7,8]. The Ni nanocrystals had orientation relationships to the geometry of the focused ion beam, that was, {111}f.c.c. parallel to the irradiated plane and f.c.c. parallel to the projected ion beam direction. Ni-11.5wt.%P amorphous alloy pre-annealed at 473 K for 250 hours showed a fluctuation of P concentration in the range of 6-to 10 wt.%. After the pre-annealing, the size of N
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