Ｍｎ‐Ｚｎフェライト単結晶の塑性変形

Abstract

Plastic deformation of Mn-Zn ferrite single crystal was investigated by constant stress and constant strain rate tests. The crystal samples were compressed along[001], [110]and[111]axes at temperatures between 1000°and 1400°C. The samples deformed along[001]axis were quenched and their etched surface was observed. Rows of etch pits on (110) plane were thought to represent slip dislocations.In the constant strain rate tests, yield drop was observed at relatively low temperatures, accompanied by a drastic increase of etch pit density just after the upper yield point.At a constant strain rate (1.9×10-4sec-1), {110} slip was thought to cause yielding for[001]compression at the temperatures tested (1000°to 1450°C). For[110]and[111]compressions, it appeared that different slip systems caused yielding depending on temperature. It was indicated that {111} planes were slip planes at yielding in the higher temperature region. However, yielding in the lower temperature region was caused by slips on {110} planes for[110]compression, and by slips on {100} planes for [111]compression.The activation volume for flow under[001]compression ranged from 20b3 at lower stresses to 5b3 at higher stresses. The activation energy at lower temperatures (≤1200°C) was 60 to 80kcal/mol and was extrapolated to 135kcal/mol at τ=0. The rate-controlling mechanism at lower temperatures was thought to be thermally activated overcoming of Peierls-Nabarro stress rather than dislocation climb (diffusion). The low activation energy (10 to 30kcal/mol) was obtained at higher temperatures. It was suggested that interpenetration on intersecting slip planes, diffusion and cross slip occured.