Microtexture analysis of Zr-2.5Nb pressure tubing

Extruded and cold-worked Zr-2.5 wt%Nb pressure tubes contain ex-phase grains that are mostly platelets (containing about 1 wt% Nh in solution) having aspect ratios of about 1:5-10:20-40 in the radial, transverse and longitudinal axes of the tube respectively. In many cases these platelet grains are oriented with their c-axes within about 20 degrees of the transverse direction. In addition to these platelet-like grains, that formed during the extrusion process, there are a significant proportion of other grains that existed prior to extrusion. These "prior-alpha" grains are subject to deformation during extrusion, and the extent of flattening is dependent on their crystallographic orientation relative to the deformation path in passing through the extrusion die. The net effect is that grains with c-axes oriented towards the radial direction are flattened less than those of other orientations and appear more equiaxed when viewed parallel with the longitudinal axis of the extruded tube. This relationship between grain morphology and orientation has been studied using Electron Back-scatter Diffraction Pattern (EBDP) analysis and the results show that for the deformed "prior-alpha" grains there are two distinct populations of grains: (a) one equiaxed in the radial-transverse plane having c-axes close to the radial direction; and (b) one flattened in the radial direction with c-axes close to the transverse direction. Subsequent cold-working of the as-extruded tube introduces dislocations into the grains and the dislocation structure is dependent on grain orientation.