Unlubricated pin‐on‐disk wear tests of Si 3 N 4 against tool steel and gray cast iron were performed at 5 N of normal load, 0.5 m/s of sliding speed, and environmental temperature in the range 22°‐600°C. The friction coefficient of Si 3 N 4 sliding against tool steel and gray cast iron had maximum values of 0.88‐0.98 for tests at 100°C. The friction coefficient of Si 3 N 4 sliding against gray cast iron couples had minimum values of 0.48‐0.57 at 400°C. Because of the increased third‐body protection, the wear coefficient of the Si 3 N 4 pins of the Si 3 N 4 /gray cast iron couples decreased by 1 order of magnitude from 1.6 10 ‐5 mm 3 /(Nm) at room temperature to 1.3 10 ‐6 mm 3 /(Nm) at 600°C. Fe 2 O 3 and Fe 3 O 4 resulting from tribooxidation of the metallic disks were the main constituents of the wear debris and adherent tribolayers. Activation energy values (6.3‐13.7 kJ/mol) were comparable to those of oxidation wear of steel (7.3‐11.8 kJ/mol) but were much lower than the activation energy for oxidation of iron alloys in static conditions. Calculations of the activation energy of the oxidation wear corroborate the morphological observations of a sacrificial action of the metallic surface protecting the ceramic material.
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Gomes et al. (1999) studied this question.