Optical and electron microscopy of niobium crystals deformed below room temperature

Pure niobium crystals have been deformed at 77 and 158 K at a strain rate 8 × 10−1 s−1. For crystals with a wide range of Orientations the deformation took place mainly by slip on the anomalous (011) plane. The nature and extent of the slip lines were studied by optical microscopy using Nomarski interference contrast. Thin foils were prepared from many crystals, with sections being taken parallel to a number of planes, and examined in a transmission electron microscope. The dislocation structures observed are described in some detail. A model for anomalous (011) slip is proposed which explains many of its characteristics.