Electronmicroscopical Study of the Formation of Iron Carbide Phases After High-fluence Carbon Ion Implantation into Iron
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Electronmicroscopical study of the formation of iron carbide phases after high-fluence carbon ion implantation into iron at low temperatures C. Hammerl,a) A. K¨oniger, and B. Rauschenbach Institut f¨ur Physik, Universit¨at Augsburg, D-86135 Augsburg, Germany (Received 5 August 1997; accepted 27 October 1997)
Carbon ions were implanted with energies between 50 and 150 keV into thin iron layers at temperatures of 210 ±C and 270 ±C. Formation of iron carbide phases was studied as a function of fluence, which was varied from 1.2 3 1017 C1 -ionsycm2 up to 1.4 3 1018 C1 -ionsycm2 . The sequence of phase transformation during subsequent annealing to temperatures of up to 450 ±C was also investigated. Detailed analysis of structure and morphology was done by cross-sectional transmission electron microscopy and electron diffraction experiments. The existence of metastable iron carbide phases, u-Fe3 C, x-Fe5 C2 , h-Fe2 C, and also the amorphous phase Fe(C), after high-fluence carbon ion implantation and the transformation of the formed metastable phases by subsequent annealing into the u-Fe3 C phase are demonstrated.
I. INTRODUCTION
Chemical and tribological properties of pure metals and alloys are known to be clearly modified by high-fluence ion implantation (see, e.g., Refs. 1 and 2). Although strong progress has been gained in the understanding of the experimental factors responsible for the observed improvements of the material properties, the phase formation during implantation and the transformation of implantation-induced phases are not yet well understood. In particular, it has been demonstrated that the nitrogen ion implantation in iron leads to different metastable phases.3–5 In contrast, only a few studies are known which deal with the formation of iron carbides by highfluence carbon ion implantation, although iron and steels after carbon ion implantation also have interesting mechanical and chemical properties.6,7 The iron/carbon system is characterized by the well-known iron-cementite (u-Fe3 C, cementite), metastable crystalline iron carbide phases (e.g., x-Fe5 C2 or H¨agg-carbide, e-Fe2 C12x , and solid solutions (austenite, martensite),8 where the exact phase identification in the FeyC system is difficult because of the structural similarity of the carbide phases.9 Previous papers have shown the formation of different stable and metastable crystalline iron carbide phases at room temperature or even higher temperatures.10–14 Also, hints for amorphization of iron by carbon ion implantation at room temperature could be found.11 Recently, the formation of iron carbide phases after carbon ion implantation in iron at 270 ±C was studied a)
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2614
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 9, Sep 1998
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by x-ray diffraction15 and in situ measurements of the electrical resistivity.16 In this paper we demonstrate the existence and the morphology of metast
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