Processing Steels for Tribological Applications by Titanium Implantation
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PROCESSING STEELS FOR TRIBOLOGICAL APPLICATIONS BY TITANIUM IMPLANTATION
I.L. SINGER,* AND R.A. JEFFRIES"* *Naval Research Laboratory, Code 6170, Chemistry Division Washington, DC 20375; **Geo-Centers, Inc., 4710 Auth Place Suitland, MD 20746
ABSTRACT Titanium implantation into steels has been shown to produce superior tribological surfaces. The fluence required to produce a wear resistant surface increases from 2 to 7 5x0O1 Ti/cm2 as the energy increases from 50 to 200 keV/ion. On curved surfaces (e.g., bearings, cutting tools, etc.) higher fluences are necessary due to effects of implantation at angles off normal incidence (i.e. the combined effects of higher sputtering rates, decreased range, and changes in the carburization process associated with duty cycles). Significant improvements in friction and wear have also been observed for surfaces which have been abraded by 600 and 120 grit SiC prior to implantation. Optimal benefits of Ti-implantation are associated with the formation of a modestly thick (>20nm) fully carburized layer.
INTRODUCTION One of the most important tasks of surface processing technology will be to improve the tribological performance of load-bearing steels. Steel components such as balls, rollers, races and gears usually have sufficient bulk hardness to support the load but lack the needed " strength'' at the surface to avoid adhesive, abrasive or fatigue failure. One of the most successful candidates for reducing friction and wear of bearing steels is Ti implantation [1-4]. Investigations of Tiimplantation in the most common of all bearing steels, AISI 52100 steel (Fe-1.5Cr-lC by wt.%), have found reduced friction under dry and poorly lubricated sliding [1,2], increased abrasion resistance [5] and increased scuffing resistance [2,3]. However, the benefits are obtained only when implantation is performed to high fluence, where an amorphous Fe-Ti-C layer forms in the surface [2] of this layer. Recent investigations [69] of what we call the implant-assisted vacuum carburization process have established a chemical basis for producing this superior tribological surface in 52100 steel by Ti-implantation. The intent of this study was to establish the processing parameters that optimize the tribological benefits of Ti-implantation. The processing parameters investigated were fluence, energy and angle of ion implantation. Dry sliding friction and wear measurements were performed on polished and abraded 52100 steel disks. Auger sputter profiling was used to give a chemical basis for the observed tribological behavior.
EXPERIMENTAL Friction measurements were carried out in air (-50% RH) at room temperatures at a sliding velocity of 0.1 mm/s. The sliders were 1.27 cm diameter AISI 52100 steel balls (R = 60) which were in contact with c
Mat. Res. Soc. Symp. Proc. Vol. 27 (1984) oElsevier Science Publishing Co.,
Inc.
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The applied force was steel disks C.95 cm in diameter and 0.32 cm thick. The first passes were 5 mm in 9.8N, giving a Hertzian stress of 0.85GPa. length; subsequent passes ove
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