Slip patterns made by sphere indentations on single crystal MnZn ferrite

Abstract

Crystals of MnZn ferrite are deformed by indentation with a loaded sphere. On all planes studied, (100), (111) and (110) the deformation consists of slip lines, above a certain threshold of stress. At higher loads new lines appear, apparently coupled to the first ones. At still higher loads cracks are found as well. The slip patterns are discussed for {100}, {111} and {110} slip systems with a Burgers vector along <110>. The analysis is supported by calculations of the resolved shear stress (RSS) on the basis of the elastic equations for a halfspace loaded by a sphere. The source of dislocations is located where the RSS is largest. From there slip propagates into the sample and to the surface. The predicted position and orientation of the lines on the surface agree with experiment. Depending on the plane of indentation, slip starts on {100} or {111}, then continues on the other systems. The observed cross-slip requires an extension of the RSS model used here.