A Ni-10.8Cr nanocomposite (by wt.%), consisting of nanocrystalline Ni matrix (mean grain size: 60 nm) and dispersed Cr nanoparticles (mean particle size: 42 nm), has been synthesized by nanocomposite electrodeposition. The unique structure causes the nanocomposite to form a double-layered nitrided zone during plasma nitridation Lit 560 degrees C for 10 h. The outer layer (similar to 50 pro thick) precipitates nanometer-sized CrN (< 100 nm), which increased in size but decreased in number with increasing nitridation depth (following Bohm-Kahlweit's mode). The inner layer (similar to 5 pin thick) exhibits larger-coarsened nitride precipitates (100-200 nm) which almost link together. The greatly enhanced nitriding kinetics in the nanocomposite compared to a compositionally similar but microstructurally different Ni-10Cr alloy (mean grain size: 30 km) is mainly associated with the fact that the numerous grain boundaries dramatically increase the nitrogen permeability, according to the treatment using a classical Wagner's approach. The nanohardness profile in relation to the microstructure of the nitrided zone in the nanocomposite has also been investigated. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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chinese acad sci, state key lab corros & protect, inst met res, shenyang 110016, peoples r china.;peng, x (reprint author), chinese acad sci, state key lab corros & protect, inst met res, 62 wencui rd, shenyang 110016, peoples r china;xpeng@imr.ac.cn
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