The Formation of Metal Carbide Layers by Elevated-Temperature Ion Implantation of Fe-Based Alloys
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THE FORMATION OF METAL CARBIDE LAYERS BY ELEVATED-TEMPERATURE IMPLANTATION OF Fe-BASED ALLOYS J.A. SPRAGUE AND I.L. SINGER Naval Research Laboratory, Washington,
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DC 20375-5000
ABSTRACT 0
An Fe-i % C alloy 7 has been 2 implanted at approximately 600 C with V to ions/cm and with Nb to a fluence of 3 x 1017 a fluence of 5 x 101 ions/cm2. For both implantations, Auger analysis showed that a nominally Below this stoichiometric metal carbide layer formed beneath the surface. layer, which was depleted of Fe, the metal carbide concentration decreased TEM gradually, giving a continually graded interface with the bulk. which analysis showed a continuous layer of fine-grained VC or NbC, with the orientation relation Baker-Nutting displayed a preferred underlying a-Fe matrix.
INTRODUCTION Ion implantation is a well-established technique for the modification This processing is of surfaces of metals, semiconductors, and ceramics. most often carried out at or below room temperature, for the purpose of A good example of stabilizing non-equilibrium phases and microstructures. this type of processing is the implantation of steels with elements such as Such implantation, when Ti, Cr, Ta, and Nb, which readily form carbides. performed in conventional high vacuums, results in the formation of a vacuum-carburized layer, which has low coefficient of friction and good Investigations of these vacuum-carburized layers have wear resistance [1]. shown that they are amorphous mixtures of Fe from the substrate alloy, the [1,2], and carbon from the residual implanted carbon-active element The concentration depth atmosphere of the implantation chamber [3]. profiles of the implanted elements in these layers are those predicted for ion implantation modified by sputtering [4,5], with carbon concentrations that are a maximum at the specimen surface and decay to bulk values within the implanted layer. When the implantation was carried out with Ti ions at elevated temperatures (600 - 800 C), significant improvements were again seen in the friction and wear properties of a bearing steel, but the metallurgical changes were very different from those produced by room temperature TEM investigations found a crystalline TiC layer with a implantation [6]. Auger analysis preferred orientation with respect to the underlying alloy. indicated that the C concentration followed the profile of the implanted Ti at a ratio of approximately 1:1. The TiC layer was covered by a layer rich SIMS analysis showed that the source of the C in the layer was the in Fe. it contained greater than 0.2 wt.% C, and was the substrate alloy, if for lower-carbon chamber of the implantation residual atmosphere substrates. Elevated-temperature implantation processes for forming graded carbon layers in metal surfaces have practical ramifications as well [6,7]. The current experiments were undertaken to investigate further the The formation of carbide layers by elevated-temperature ion implantation. elements chosen, V and Nb, both are known to form MC carbides, but their phase diagr
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