STUDIES OF DEFORMATION IN NIOBIUM BY X-RAY TOPOGRAPHIC METHODS.

We have studied plastic deformation in niobium crystals by a variety of x-ray topographic techniques including: Lang topography, double crystal topography and synchrotron white beam topography. The limitations of these direct methods, which rely on the resolution of individual dislocation segments, are illustrated by our results. An indirect topographic method, contour mapping, is described for use with specimens which cannot be profitably studied with the direct techniques. The positions of equi-inclination contours (analogues to TEM bend contours) are recorded as a function of specimen rotation, allowing measurement of the components of the strain tensor as a function of position on the specimen. The use of monochromatic radiation and of synchrotron white radiation are described and results obtained with contour mapping are summarized.