Defects formed within hardness indenter interaction zone in Al 2 O 3 –ZrO 2 composite

Summary The Al 2 O 3 −10 wt% ZrO 2 composites were subjected to hardness tests using a Vickers diamond indenter up to 98.1 N. The microstructure observation using a transmission electron microscopy technique helped to identify up to four zones differing in defect level and character. The densest dislocation tangles, twins accumulation and frequent presence of three slip systems were found in regions that were in contact with the sides of the diamond pyramid. The second zone, characterized by two, or at least one, active slip systems, started at the bottom of the indentation mark and extended up to a distance comparable with the depth of indentation. In the third zone, with a thickness comparable to that above, only some α‐Al 2 O 3 crystallites showed the presence of dislocations, whereas other crystallites were defect free. In the last zone the alumina crystals were left unaffected but the ZrO 2 crystallites showed twinning characteristic of strain‐induced transformation.