Tribology of Amorphous Alloys Formed With Ion Beams
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TRIBOLOGY OF AMORPHOUS ALLOYS FORMED WITH ION BEAMS D. M. FOLLSTAEDT, J. A. KNAPP AND L. E. POPE Sandia National Laboratories, Albuquerque, NM 87185-5800 ABSTRACT The changes in friction and wear properties (i.e., tribology) of steels due to thin surface alloys formed by ion beams are surveyed, and considered in light of their microstructures. Amorphous alloys containing both Ti and C are found to give superior performance in comparison to alloys with N, B, C, P or Ti. All the amorphous layers reduce friction, but the duration of benefits and wear resistance at high loads vary with composition. By examining similar amorphous alloys with Ti alone or C alone, the critical roles played by each in resisting wear are demonstrated. Amorphous alloys with Ti and C appear to be quite hard. INTRODUCTION Ion implantation has been developed during the last two decades as a method to modify the near-surface region (.' 1 m) of metals to alter their chemical [1] and mechanical [2] surfacerelated properties. Despite the thinness of the implanted layer, significant benefits are readily achieved. The treatment can reduce friction coefficients and wear rates of an unlubricated sliding wear couple when the proper elements are implanted into one member [3]. An example of the significant reductions obtainable is shown in Fig. 1 with 304 stainless steel (SS), where the friction coefficient is reduced by implantation from 0.7 to 0.3, and the wear depth from 1 pm to 0.2 pum. The electron micrographs show that these reductions are accompanied by a change from an adhesive wear mode, in which material is torn out of the wear track, to an abrasive wear mode for which only sliding grooves are seen. Improvements in mechanical properties have been obtained for a number of metals [2], but here we examine work done on steels and some supporting results from Ni and Co alloys. The unlubricated sliding friction and wear results for several implanted species and other ion-beam alloying methods will be surveyed to identify the most promising treatments, and used with characterizations of microstructure to elucidate important aspects of the tribology of implanted steels. This will lead us to focus on amorphous surface alloys, especially those produced by implanting Ti and C together.
a) FRICTION IT
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0 I.z w 0.4 UL IAi. LL U.i
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b) WEAR SURFACE
WEAR CYCLES
Figure 1.
and a) Friction traces for 440C pin 2 with 12 g load on 304 disks, unimplanted 2 implanted with 2 x 1017 Ti/cm , 180-90 keV, plus 2 x 1017 C/cm , 50 keV. b) Scanning electron micrographs of the corresponding wear tracks.
Mat. Res. Soc. Symp. Proc. Vol. 128. c 1989 Materials Research Society
390
General Features of Ion-Implanted Metals Ion implantation has several advantages over other surface treatments, as well as some disadvantages. A major advantage is that any element can be introduced into any material, often to high concentrations (10's of atomic percent), independently of usual thermodynamic alloying constraints; thus m
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