Regularities of Changes in Kearns Texture Coefficient at Cold Rolling of Zr-2.5%Nb Alloy

Abstract

-ray studies of the changes in characteristics of crystallographic texture with cold deformation of Zr‑2.5%Nb alloy plates by longitudinal and cross rolling up to 56% at the speed of 5…10 sec-1 were carried out. The original plates were made from longitudinal fragments and rings cut from Æ15.0´1.5 mm² tube, and were then annealed at 580 °C. Texture of the plates was studied by the method of inverse pole figures with calculation of the Kearns texture coefficient along the normal to the plate plane. Dependences of the texture coefficient on degrees of deformation of the plates are built. A discrepancy was found between texture coefficient values measured on different sides of the plates, which is associated with the straightening of the original tube fragments and invariance of “c”-axes distribution after subsequent annealing of the initial plates. By introducing corrections to the degree of deformation calculated from the parameters of the cross section of the original tube, such discrepancies were eliminated for the data on cross-rolling of the material. As a result, for both deformation schemes, two stages of changes in the texture coefficient with alloy deformation were revealed: the initial stage of its growth and the subsequent stage of minor changes. Both stages are mainly linear and have the boundary value of the texture coefficient equal to 0.65...0.68. To study the structural mechanisms of changes in the texture of the alloy, an original technique of comparative analysis of changes in the texture coefficient of the material and in the distribution of crystallographic orientations is applied. It is established that at the initial stage of changes in the texture coefficient with deformation in both schemes, the rotation of the crystallographic “c” axes of the material occurs abruptly, and it does at angles of more than 60°. This confirms the essential role of twinning in the texture changes of the alloy. In particular, we have shown that the initial stage is significantly dominated by the {102}á011ñ system of tensile twins. Connection of twinning with differences in texture changes at the longitudinal and cross rolling of the alloy is discussed.

Surface Purity Effect on Irregularities of Changes in Deformation Texture of Zr-2.5% Nb Alloy

“…According to preliminary studies, the texture of the tube turned out to be similar to the usual rolling texture of plates which rolling direction coincides with the tube axis [2]. A distinctive feature was its fan-like shape -the moderate character of its distribution along cross section of the tube.…”

“…According to the experience of work [2,4], the deformation degrees were corrected taking in account its inhomogeneity along the thickness of the plates. The correction was calculated based on the values of the thickness and diameter of the original tube -and was introduced as a deformation of the medium on the surface of the original plates similarly to rolling.…”

“…This work is a supplement to the cycle of X-ray studies of regularities of changes in the crystallographic texture during cold deformation of zirconium and its alloys [1][2][3]. A feature of such works is the implementation of X-ray studies of rolling textures from their moderate level and the use of the method of inverse pole figures (IPFs) with an increased accuracy of determining the quantitative texture characteristics.…”

“…Preliminary studies have established that this effect is initiated on the surface of deformed plates [4]. Comparison of the results of works [2][3][4] gives reason to assume that this is due to surface impurities. Such a circumstance can occur under usual conditions of materials machining.…”

“…The main subject of the research is the Kearns texture parameter (TP) [1,2,5]. Many characteristics of zirconium alloys and other metals with hcp lattice are associated with it.…”