REGULARITIES OF CHANGES IN KEARNS TEXTURE COEFFICIENT AT COLD ROLLING OF Zr-2.5%Nb ALLOY

X-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 empty set15.0x1.5 mm(2) tube, and were then annealed at 580 degrees 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 degrees. 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 {10 (1) over bar2}<<(1)over bar>011> system of tensile twins. Connection of twinning with differences in texture changes at the longitudinal and cross rolling of the alloy is discussed.