The effect of the counterface on the wear resistance of certain alloys at room temperature and 750degC

Wood, Philip David (1997) The effect of the counterface on the wear resistance of certain alloys at room temperature and 750degC. Doctoral thesis, University of Northumbria.

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Abstract

The overall aim of this research was to investigate the room temperature and high temperature wear of a group of alloys, Ma956, PM2000, PM2000SD, TiAI, Nimonic 90 and Nimonic 80A (cast and HIPped), selected to portray candidate engine valve materials, when in contact with different counterfaces (Incoloy 800, Stellite 6 and Si3N4). The counterfaces were chosen to represent seat insert materials. Wear testing was conducted on a specially constructed reciprocating wear rig designed to simulate valve seat/seat insert wear. The test conditions included: 7N load, rotation speed of 12.5m/min, 3 reciprocation cycles per minute and temperatures of 21°C and 750°C. Testing was carried out in a laboratory air environment for 4 hours.
The counterface was seen to have a major effect on the wear resistance of the alloys. The process of wear at room temperature was associated with the transfer of counterface material to the alloy surface. The degree of such transfer was dependant on the hardness of the counterface. No glaze formation occurred at room temperature.
At 750°C, the type of counterface influenced the formation of oxidised wear resistant plateaux ('glazes'). Glaze formation resulted in low friction and low weight losses. Preoxidation improved the wear resistance of the ODS alloys worn against Incoloy 800 at 750°C by forming a wear-protective oxide film on the surface of the alloy, though it did not encourage the formation of glazes. Temperature, however, did have a major influence on glaze formation on Ma956 when worn against Stellite 6. The mechanism of glaze formation involved transfer of material, oxidation, mixing, fracture, agglomeration and compaction.

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