Sliding of alumina (87%) pins against a hardened steel disk over a range of pressures (3.3-30.0 MPa) and speeds (0.1-12.0 ms-') has been studied. Four different regions (Rl, R2, R3, and R4) of friction as a function of speed have been identified. R l and R3 exhibit single-valued friction while in R2 and R4 the friction exhibits dual behavior. The speed range over which these regions prevail is sensitive to the pressure. R1 and R2 are low-speed and low-temperature regions, and in both, metal transfer and formation and compaction of y-Fe,O, occur. R3 and R4 are associated with high speeds and high interface temperatures. Formation of FeO, FeAI,O,, and FeAIO, has been observed. The implications of the tribochemical interactions on friction and wear characteristics are discussed.
Wear studies on a glass-ceramic dental restorative material were performed under two types of lubrication conditions with distilled water. In one set of experiments, the contact interface was continuously flushed with fresh water to remove the wear debris. In a second set of experiments, the water was not replaced during the testing period. Flushing resulted in a lower friction coefficient and more than twice the wear volume compared with the nonflushing condition. Examination of the worn surfaces in SEM confirmed the presence of an interfacial layer at the sliding interface for the nonflushing experiments. These results suggest that the specific conditions at the sliding interfaces and particularly the nature of interfacial layers must be considered when evaluating the tribological performance of ceramics and especially when the wear data from different studies are compared.
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