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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

ww values

ww values of all MMCs were less than half that value. TOPC10IS had the highest wear of all MMCs. The Al2O3-reinforced MMCs (AOPC20IS and AGPC15IS) had similar ww of around 300 µm. MOPC20IS and FATOIS had lower values of 260 µm and 250 µm respectively. Width Width of wear of wear path path w ww (µm) / µm w 700 600 500 400 300 200 100 0 IS AOPC20IS AGPC15IS TOPC10IS MOPC20IS AODY30IS FATOIS Figure 4.82 Characteristic friction coefficient f50m and width of wear path ww after wear test of unreinforced and MMC materials. In contrast to AOPC20IS, AODY30IS showed no distinct wear path after the test. Only wear pits in the ceramic phase and some small local metallic regions about 25 µm wide, such as that on the left of Figure 4.83 b), were found. In the metal areas, no contact with the sliding cylinder was detected compared to the other MMCs. Therefore, the tribological pairing of AODY30IS with steel has to be assumed to between steel and pure alumina with the contact area interrupted by the circular metallic domains. 183 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 Friction Friction coefficient coefficient f f50m ( ) 50m

a) b) 2 50 2 50 µm µm 2 50 2 50 µm µm Figure 4.83 Structure of the wear path after tribological test run. a) AOPC20IS and b) AODY30IS. In FATOIS, a phase with a higher density accumulated along the edge of the wear path as indicated by the light area in Figure 4.84 a) which EDS analysis showed to be an iron and chromium-rich phase shown in Figure 4.84 b). As a chromium-containing 100Cr6 bearing steel was used for the cylinder, the light phase was transferred from this to the MMC surface. Figure 4.83 shows the wear paths of the AOPC20IS and AODY30IS alumina-reinforced composites. The structure of AOPC20IS had deep grooves which could not be resolved with the optical microscope. The groove wear was parallel to the sliding direction of the counterpart cylinder as indicated in Figure 4.83. A light grey phase enclosed a darker fibre-shaped phase outside the wear path of Figure 4.84 b). The grey phase was the titania particles and the darker enclosed phase the alumina fibres. In Figure 4.84 b) an accumulation of worn steel is visible which enclosed a fragmented alumina fibre (circled). This had a larger diameter than the other fibres visible in the image and which had a nominal diameter of 3 µm. Furthermore, the small aspect ratio of less than 3 indicated that it was a fibre shot, a by-product of fibre fabrication. The accumulation of the steel debris in the vicinity of the shot has to be attributed to its increased abrasive effect compared to the normal fibres. 184

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