Nitride formation in iron after nitrogen implantation in a nickel top layer
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Nitride formation in iron after nitrogen implantation in a nickel top layer D. K. Iniaa) Department of Atomic and Interface Physics, Debye Institute, Utrecht University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
F. D. Tichelaar National Center for HREM, Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands
W. M. Arnoldbik and A. M. Vredenberg Department of Atomic and Interface Physics, Debye Institute, Utrecht University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
D. O. Boerma Department of Atomic and Interface Physics, Debye Institute, Utrecht University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands and Department of Nuclear Solid State Physics, Materials Science Center, Groningen University, Nijenborgh 4, 9747 AG Groningen, The Netherlands (Received 25 March 1997; accepted 31 July 1997)
Nitrogen was introduced in an iron layer underneath a top layer of nickel. This was done by ion implantation of N into the Ni layer at a temperature of 200 ±C. During implantation and subsequent anneals at 250 and 300 ±C, N diffuses from the Ni layer into the Fe layer because of a larger affinity of Fe for N than of Ni for N. The concentration depth profiles of N in the NiyFe bilayers, as recorded with the nuclear reaction analysis technique, show at the highest implantation dose a peak below the NiyFe interface. From structural analysis techniques (x-ray diffraction and cross-sectional transmission electron microscopy) it was observed that this peak is due to the presence of an e–Fe32x N layer below the NiyFe interface. It is thus shown that e –nitride can be formed in Fe at such low temperatures in the absence of radiation damage.
I. INTRODUCTION
Ion implantation of nitrogen in iron and steels is a widely applied technique to obtain improvement of material properties such as hardness and wear and corrosion resistance. To understand the phenomena that play a role during implantation, such as diffusion of nitrogen and nitride formation, many implantation studies have been performed over the last two decades (for a review see, e.g., Ref. 1). Major advantages of ion implantation over other methods of surface treatment are the control of the implanted nitrogen dose and the low process temperature. Since iron nitrides are metastable, this low process temperature is important for the synthesis of iron nitrides (e.g., in low-alloyed steels). In a thermochemical nitriding treatment, where the iron workpiece is heated in, for instance, a NH3yH2 atmosphere, process temperatures of 500–600 ±C are used. At these temperatures the formed iron-nitride layer (consisting of g′–Fe4 N and e –Fe3–x N) can be porous due to the decomposition of the nitrides into Fe and N2 gas, which is thermodya)
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J. Mater. Res., Vol. 13, No. 2, Feb 1998
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namically favorable.2 At lower temperatures used in ion implantation this d
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