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Another major improvement resulting from the surface modification of the ceramic disks by ion beam mixing was the reduction in wear of the pin disk combinations to the extent that in many cases, the amount of wear could not be measured either by weight change or by surface profilometry. For combinations 1 through 4 involving the Ti-Ni modification, and combinations 7 and 8 involving the Ni modification, thé wear track on the disks was barely discernible by eye or in the electron microscope. The morphology of the wear process will be discussed in the following section.

Surface Analysis

Pins from pin-disk combinations 1 through 6 showed a wear mark which appeared to be a layer of material which had transferred from the disk to the pin surface during sliding contact. AES analysis showed that this was indeed the case, the transfer layer containing nickel (and possibly titanium) transferred from the TiNi modified disks [22], and Co transferred from the Co modified disks. Pins run against the Ni modified combinations 7 and 8, as well as those run against Cr modified disks (not shown in Table 1), show no such transfer layer, instead evidencing a large amount of delamination-type wear as described by Suh [26].

Wear of the modified surfaces did indeed occur to varying degrees. Previous study of the Ti-Ni modified disks indicated that the modified layer showed evidence of del amination wear [21,26], with the disks having higher coefficients of friction (combinations 2 and 3) showing larger amounts of wear than those with the lower coefficients of friction. Elemental Auger maps of these wear surfaces showed that delamination occurred along the modified layer-substrate interface. Auger depth profile analysis of the modified layers indicated that poor mixing of the modified layer with the substrate may have been a cause for the delamination of the layer, see Fig. 2a. However, subsequent mixing and oxidation of the modified layer at the high temperatures expected at the contact surfaces during testing apparently Ted to the improved friction and wear behavior observed in the simulated diesel environment, especially for the modified Si3N4 disks, see Fig. 2b.

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