Shape Change of Crystal Grain and Grain Boundary of Polycrystalline Ni-Zn Ferrite Under Compressive Deformation

Abstract

Polycrystalline Ni_0.5Zn_0.5Fe₂O₄ (density, 99%; average grain size, 60 microns) was deformed under the compressive load. The brittle-ductile transition temperature was about 1200°C under the loading rate of 11kg/cm²⋅min. In the compressive deformation at higher temperatures than 1400°C, straight slip lines, interpenetration of 60° and 120° slip systems as well as wavy slip lines, were observed. Grain boundary slip was not large enough to be observed by the off-set of the marker line even in the temperature range of ductile fracture. During the compressive deformation, grain boundary migrated to the perpendicular direction to the grain boundary plane and lost the flatness of the boundary. And also, corrugation and rumpling of grain boundary were observed during the deformation process. These seem to be the causes of the difficulty of grain boundary slip. In the vicinity of grain boundary, the deformation by dislocation movement was active as seen by corrugation and rumpling of grain boundary. However, the piled-up dislocations near the grain boundary and ensuing strain were not relaxed by a mechanism like polygonization in the temperature range of this research.