Observations on the role of the steel disc counterface during the sliding of various structural ceramics

Abstract

Sliding wear characteristics and mechanisms of structural ceramics, namely A1 20 3, zirconia-toughened alumina, tetragonal zirconia polycrystals (TZP) and Si 3N 4 against a steel counterface are influenced by mechanical and tribochemical interactions, specific to the combinations studied. The present paper studies the role of the disc in the sliding wear process of the above ceramics. Experiments were conducted at a pressure of 15.5 MPa between 0.1 and 12.0 m s −1 with ceramic pins sliding against an EN-24 steel disc. Except in the case of TZP, the disc morphology is sensitive to variations in speed rather than to the pin material. The disc track is (i) mildly abraded at low speeds (about 0.1–0.75 m s −1), (ii) severely abraded at intermediate speeds (about 1.0–3.0 m s −1), (iii) covered with black patches at high speeds (about 4.0–6.0 m s −1) and (iv) completely black at very high speeds (about 7.0–12.0 m s −1). In the case of TZP, although black patches appear, transfer of TZP onto the disc surface and high wear of TZP occurs at 4.0 m s −1. The order of the wear of the disc estimated from profilometric measurements is the same for all the ceramics. Except for Si 3N 4, the onset of wear of the ceramics is associated with the appearance of deep ‘V’ grooves on either side of the profile of the disc track. This can be explained on the basis of the thermal and hardness variations. Although other interaction products specific to the ceramic pin are present, the formation of iron oxides dominates the wear of the disc.