Untersuchungen im Anfangsbereich der Verformungskurve von Eisen-Einkristallen

Abstract

The stress-strain curves of iron single crystals at room temperature and at −78°C (strain rate$\dot s$=5·5.10⁻⁵ sec⁻¹) are characterized by a dynamical yield point followed by a strong work-hardening. The plastic deformation starts by the movement ofa/2〈111〉 dislocations from several places of the specimen. Macroscopically, the dislocations move approximately along the planes with maximum resolved shear stress. Slip bands are formed by multiplication of the moving dislocations. They broaden and fill the whole specimen at a strain smaller than 0·1% or 0·2% for the deformation at room temperature and −78°C respectively. The corresponding dislocation densities are <4.10⁶ cm⁻² and ≃2.10⁷ cm⁻² respectively. At these strains a strong work-hardening begins. The mosaic structure causes an increase of the yield stress and of the difference between the upper and lower yield stress. Differences between iron and iron-3% Si alloy single crystals at the beginning of the plastic deformation have only a quantitative character and can be explained by the fact that the lattice friction stress in iron is approximately 15 times smaller than in iron-3% Si alloy.