Surface-Chemistry-Driven Tribological Fundamentals of Diamond and SiC for Extreme Environment MEMS Applications
Final rept. 1 Aug-31 Dec 2000
RAYTHEON CO EL SEGUNDO CA
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Environmental SEM tribometry of the pressureless-sintered Hexoloy alpha-SiC ceramics was continued in 0.2 and 3.4 Torr partial pressures of oxygen Po2 at room temperature RT to 95O deg C, coupled with after-test SEM photomicrography and AESXPS surface analyses of the wear scars and the adjacent unused surfaces. The results show some correlation in the somewhat improved friction behavior of both the previously tested CERCOM SiC-B in partial pressures of oxygen compared to vacuum, especially when the slower tribo-oxidation kinetics and the surface-oxide-induced reduction in grain pull-out of the boroncarbon-pressed Hexoloy are taken into account. Even in the presence of the thickest lubricating film formed at the 3.4 Torr PO2, the COF still did not become reduced below -0.2 and the MAX.COF below 0.3. These values are an order-of-magnitude higher than those of the polished PCD. The same observation was made with the SiC-beta previously. The wear rate of Hexoloy is only slightly albeit consistently less in oxygen than that of the SiC-beta, with both in the 10-15m3N x m range an order-of-magnitude greater than PCD. Considering the overall tribological behavior of both alpha-SiC materials, neither is able to serve better than PCD in MEMS moving mechanical assembly applications intended for extreme environments.
- Electrical and Electronic Equipment
- Lubricants and Hydraulic Fluids