In Situ Ultrahigh Vacuum Friction Measurement and Wear Track Analysis of Ion Implanted 304 Stainless Steel
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IN SITU ULTRAHIGH VACUUM FRICTION MEASUREMENT AND WEAR TRACK ANALYSIS OF ION IMPLANTED 304 STAINLESS STEEL* LARRY E. POPE, DAVID M. FOLLSTAEDT, JAMES A. KNAPP AND J. Sandia National Laboratories, Albuquerque, NM 87185.
CHARLES BARBOUR
ABSTRACT The dual ion implantation of Ti and C into 304 stainless steel has been found to reduce friction and wear in ultrahigh vacuum (UHV). The implantation treatment producing this result, 4.6 x 1017 Ti/cm2 (180 keV) followed by 2.0 x 1017 C/cm2 (50 keV), produced TiC precipitates dispersed in an amorphous surface layer. Friction and wear track compositions were measured in situ with a scanning Auger microprobe without removing the pin from the track. This treatment decreased the friction coefficient from 1.2 to 0.6-0.8 and the wear track width from 342 pm to 225 pm after 1000 cycles. Relative to unimplanted 304, wear tracks formed in UHV and air on implanted '304 had more N and less C. Oxygen and the metallic elements were similar in concentration, except for the presence of implanted Ti. Friction coefficients measured in air were less than those in UHV; track composition suggests that oxides or adsorbed moisture helped lower the friction in air.
INTRODUCTION Ion implantation is being examined at many laboratories as a method to improve the surface mechanical properties of metallurgical components. The implantation of Ti and C reduces both the friction coefficient and the wear of steels; these results have been obtained by at least three groups using different tests on a range of steels [1-3]. This treatment has been evaluated in at least two application areas; one involving 440C ball bearings for cryogenic pumps used in liquid fuels for the space shuttle main engine [41 and the second involving a 15-5 PH discriminator wheel (5]. Encouraging results were obtained for both cases. High fluence implantation of Ti and C into 304 and Nitronic 60 (austenitic) SS and into 440C and 15-5 PH (martensitic) SS produces an amorphous layer [6]. For 304 SS implanted with Ti and C (304(Ti,C)), it was shown previously that the amorphous film was present in wear tracks when reduced friction and wear was measured; the sliding action did not crystallize the amorphous material [7]. In addition, it was shown that heating 304(Ti,C) to crystallize the amorphous layer produces a dispersion of TiC particles in a mixed fcc and bcc matrix [8]. With crystallization there was a concomitant loss of the 35% reduction in friction produced by the implantation, but the beneficial wear reduction was still obtained. To obtain a more basic understanding of the mechanism by which friction and wear are reduced, we have done new testing in an in situ tribometer. We implanted 304 SS with Ti and C and have completed in situ pin-on-plate experiments to characterize its friction and wear response in air. The tribometer allowed us to extend such measurements to UHV environments. The same experiments were done on unimplanted 304 SS to allow a direct comparison 2 of results. Since the implantation of 5 x 1017 Ti/cm (180 keV)
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