Effects of DC and AC Magnetic Fields on Grain Growth in Electrodeposited Nanocrystalline Nickel
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Effects of DC and AC Magnetic Fields on Grain Growth in Electrodeposited Nanocrystalline Nickel T. Matsuzaki1 T. Yamada1, K. Jyuami1, S. Tsurekawa1, T. Watanabe1 and G. Palumbo2 1
Laboratory of Materials Design and Interface Engineering, Department of Nanomechanics, Graduate school of Engineering, Tohoku University, Aramaki aza Aoba 01, Aoba-ku, Sendai, 980-8579, Japan 2 Integran Technologies Inc. 1 Meridean Road, Toronto, Ont., Canada, M9W 4Z6 ABSTRACT The effects of DC and AC magnetic fields on grain growth in electrodeposited nanocrystalline nickel were studied. Magnetic annealing was conducted at 573K in the ferromagnetic temperature region and at 693K in the paramagnetic temperature region. Both DC and AC magnetic annealing could enhance the grain growth and produced a homogeneous grain structure at 573K. On the other hand, AC magnetic annealing shortened the incubation time for the late stage abnormal grain growth at 693K in the paramagnetic temperature region, while DC magnetic field could not affect the incubation time. INTRODUCTION Nanocrystalline material is simply defined as such polycrystalline material which has nanometer scale grain size and extremely high density of grain boundaries even half of the total volume of the material. It has been shown that nanocrystalline materials have quite unique bulk properties different from those of conventional polycrystalline materials [1, 2]. From the view point of grain boundary engineering [3], nanocrystalline materials have known potential of materials design and development because they have an extremely high density of grain boundary volume to be designed and controlled to produce a new desirable function and high performance. In particular, grain boundary microstructure characterized by the grain boundary character distribution, may govern bulk properties in nanocrystalline materials because the fraction of grain boundary volume becomes more than 50% for the grain size less than 10nm [4]. On the other hand, nanocrystalline materials are often prone to severe heterogeneity in microstructure due to abnormal grain growth, which degrades their attractive properties and produce a scatter of performance of unique properties. For practical use, enhancement of thermal stability of the microstructure is strongly required for nanocrystalline materials. Regarding abnormal grain growth in nanocrystalline materials, interesting studies have been conducted so far [5, 6], but much still remains to be solved on the thermal stability of the materials. A magnetic field can affect many metallurgical phenomena such as recrystallization [7, 8], grain growth [9] and phase transformation [10, 11]. One of the authors (T.W.) reported that the abnormal grain growth in Fe-Co alloy could be suppressed by application of a DC magnetic field [12]. Recently, we reported that DC magnetic annealing enhanced grain growth at the early stage of annealing and produced a homogenous grain structure in electrodeposited nanocrystalline nickel [13]. The purpose of this work is to study and
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