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Formation of Niobium Carbides in High-Dose Carbon-Ion-Implanted and Annealed Niobium
Published online by Cambridge University Press: 25 February 2011
Abstract
Polycrystalline niobium was implanted with 200-keV C+ ions to a total fluence of 7 × 1017 carbon ions per cm2 (C/cm2). Auger electron spectroscopy (AES) analysis showed that the carbon concentration varied from 5 to 50 at.% within a depth of about 4000 Å. Glancing-angle x-ray diffraction analysis (XRDA) and transmission electron microscopy (TEM) analysis indicated that no Nb2C phase was formed and that a buried fee NbC layer was formed in the region where carbon content exceeds about 40 at.%. The absence of Nb2C was attributed to its narrow range of solubility for carbon and the low diffusivity of carbon atoms. The possibility of the NbC precipitation by nucleation and growth or by a diffusionless martensitic transformation is discussed. When the implanted samples were annealed at 1273 K for 1 h, an orthorhombic Nb2C phase formed as spherical precipitates and the implanted carbon redistributed.
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