The effect of anisotropy on the mechanical behavior of Zircaloy-2

Abstract

The influence of ciystallographic anisotropy on the mechanical properties of Zircaloy-2 was investigated as a function of stress state and plastic strain at 273 and 623 K. Zircaloy-2 plates were tested in the cold worked, stress relieved condition. Crystallographic textures were quantitatively characterized by the Kearns texture number, f, and plotted on direct and inverse pole figures. Uniaxial tension, compression, and plane strain compression tests were performed on 1.27 cm thick plates of Zircaloy-2 having two markedly differential initial Crystallographic textures. The test data was used to construct monotonic yield loci as a function of texture and plastic strain. The complex shapes of the different yield loci indicate a strong anisotropic mechanical behavior in the low plastic strain range at room temperature. The uniaxial flow stresses were found to be a unique function of the texture number, f. The mechanical behavior of Zircaloy-2 is a strong function of the controlling deformation mechanisms and of the texture derived constraint. These deformation mechanisms include prism slip, 〈c + a〉 slip and twinning. Plastic deformation was found to cause significant texture rotation after as little as 1.5% plastic strain. The severest texture rotation occurs with {101̄2} twinning which gives an 85° rotation of the c axis. Measurements of the transverse plastic strain ratio R as a function of plastic strain were correlated with the texture number, f, and flow stress measurements. A marked strength differential effect was observed when the stress axis is parallel to a direction of high basal pole density.