The influence of carbon as a dopant on grain growth and its effect on the wear resistance of polycrystalline alumina was evaluated. Carbon was introduced into alumina by sintering in a carbon-rich environment (graphite furnace under flowing He), and/or by residual carbon from organic binders used during the green body consolidation process. Samples were sintered at 1600°C for 2 hours, and doping alumina with carbon resulted in a reduced grain size after sintering, correlated to solute-drag, or graphite particle-drag for higher concentrations of carbon (~3 wt.%). STEM/EDS was used to analyze the carbon doped samples and showed carbon adsorption to the grain surface near pores for low carbon concentrations (below solubility limit). Graphitic inclusions in pores, confirmed by EELS, were found in the sample with higher carbon concentration.
The material response to abrasive wear was evaluated by measuring the time to section samples of a defined area using a diamond wafering saw. Sintering alumina with carbon resulted in a significant increase in wear resistance. During the wear of alumina, a so called "tribo-film" is formed, believed to be a layer of wear debris, which was analyzed by TEM and EDS. The tribo-film is ~200 nm thick and contains besides Al, O and Mg (from the alumina powder) and minor amounts of Ca and F, most likely contaminants from the cooling water used during the cutting process.