Dislocations in Indented Magnesium Oxide Crystals

Abstract

Dislocation rosette patterns produced by spherical and pyramidal indentors on the cleaved surfaces of magnesium oxide crystals were studied in detail. The three‐dimensional arrangement of dislocation loops as deduced from the two‐dimensional etching patterns is discussed. Cracks formed on {110}₉₀ planes around pyramidal indentations are believed to be due to the interaction of dislocations on {110}₄₅ planes. The temperature dependence of hardness was found to be related to the widening of dislocation bands, rather than to the distance of travel of leading dislocations. Some observations were also made on the pinning of dislocations and recovery at elevated temperatures, and on the interaction of dislocations with grown‐in subboundaries.