Development of local microstructure and crystallographic texture in extruded Zr-2.5Nb tubes

We report the bulk and local crystallographic texture determined by neutron diffraction in Zr-2.5Nb tubes extruded in the alpha + beta and the beta-phase fields. Bulk textures and through-wall variations were determined using neutron diffraction. We correlate these with microstructures determined by transmission electron microscopy. With a preheat temperature of 925 K where the material is similar to 90% alpha-phase, the basal plane are distributed between radial (R) and transverse (T) directions with a small bias towards the T direction. End-to-end, and through-wall variation depends upon the prior microstructure of the billet and the balance between adiabatic heating and chilling. With a preheat temperature of 1090 K, where the material is similar to 60% alpha , the basal plane normals are predominantly transverse, more so on the internal diameter, because of the extrusion geometry. With a preheat temperature of 975 degrees C, there is a strong axial component of texture at the front end of the tube, associated with the beta- to alpha-phase transformation. This component is more pronounced at the core because of chilling of the billet. At the back end of the extrusion the texture is very similar to that produced after preheating at 815 degrees C indicating that the back of the billet was substantially transformed by the time that it entered the die. (c) 2006 Elsevier B.V. All rights reserved.