ON STRUCTURAL ASPECTS OF TEXTURE CHANGES DURING ROLLING OF Zr-2.5%Nb ALLOY

Using X-ray structural analysis, features of changes in characteristics of crystallographic texture during cold working of Zr-2.5%Nb alloy plates by longitudinal and cross rolling has been investigated. To make original plates, longitudinal fragments and rings of circle divide 15.0x1.5 mm(2) tube annealed at 580 degrees C were used. The plates were rolled at room temperature to the degrees in the range from 6 to 56% with 5.7% per pass and the rate of 5...10s(-1). Using the method of inverse pole figures with measuring by the Bragg-Brentano optical scheme, densities of reflections along normal to plane of the plates (pole densities) was determined. Based on this, distributions of orientations of c-axes of hcp lattice of the material have been analyzed. Local features of the distributions, which were attributed to signs of twinning effects in texture changes in the alloy, are revealed. At subsequent analysis, an effect of strain nonuniformity associated with prehistory of the plates was taken into account. It is established that the second stage of (moderate) changes in Kearns textural coefficient of the plates with the deformation degrees differs from the initial stage of accelerated changes by activation of compression twins. By the method of tilt scanning (of rocking curves) around the Bragg-Brentano position at registration of (0004) reflection intensities, changes in orientation distributions of c-axes in longitudinal and cross section of the plates for both parties were investigated. It is noted that the main textural changes in process of deformation of the plates occur in the crosssectional plane of the original tube and are most expressed on the cross-rolling plates. The doublet in the distributions of c-axes, characteristic for rolling texture of hcp metals of titanium subgroup, was noted just at the second stage of the texture changes in the material. Its directionality is mainly associated with the plane of cross-section of the original tube. A connection is revealed between features of the pole density distributions and expression degree of the textural doublet on the rocking curves. According to the results obtained and analysis of other publications, twinning nature of the textural doublet was confirmed and a schematic sequence of its formation was proposed with participation of compression twins of {11 (2) over bar2}<(1) over bar(1) over bar 23 > system and tensile twins of {10 (1) over bar2}<(1) over bar 011 > and {11 (2) over bar1}<(1) over bar(1) over bar 26 > systems.