Texture analysis of zirconium samples deformed by uniaxial tension using neutron and X-ray diffraction

Seven zirconium samples were studied by neutron and X-ray diffraction after deformation on uniaxial tensile machine INSTRON 5882 from strain 5% to strain 30% (strain step was 5%). Preferred orientation parameters were determined by using pole figures and inverse pole figures. The X-ray measurements were performed at theta/theta X'Pert PRO diffractometer with Cr X-ray tube. Observed data were processed by software packages GSAS and X'Pert Texture. Our results can be summarized as follows: (i) Samples prefer orientation of planes (100) and (110) perpendicular to rolling direction. (ii) The position of the basal poles is tilted by 30° from the normal direction toward the transverse direction. (iii) Samples prefer orientation of planes (102) and (103) perpendicular to normal direction. (iv) Level of resulting texture increases with deformation. The obtained results are characteristic for zirconium.


Introduction
The textured material usually exhibits anisotropic mechanical, physical and chemical properties. Preferred orientation occurs in both powder samples (shape texture) and compact samples (caused by mechanical or heat treatment of material) [1]. Looking on diffraction methods to measure textures mainly three different radiations are in use. These are X-rays produced by conventional X-ray tube or synchrotron, electrons and thermal neutrons. Basic differences in analytical use of these radiations follow from their different interaction with matter [2]. This article deals with the use of neutron an X-ray diffraction in texture analysis of alpha zirconium. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. Therefore, zirconium and its alloys are used in the nuclear industry as fuel rod cladding, especially in water reactors. In the alpha zirconium slip takes place usually on the 101 0 first order prism planes along the 〈121 0〉 direction. Slip can occur also on the 0002 basal plane in the same direction. In regions of high stress concentration, the {10-11} slip is observed. Activation of slip with 〈 〉 component was noticed on first and second-order pyramidal planes 101 1 and 112 1 in 〈 〉 direction [3]. Most common twinning modes at room temperature are 101 2 〈1 011〉 tensile twins and 112 2 〈1 1 23〉 compressive twins [3].

Samples
The alpha zirconium plate was forged and hot rolled to the thickness 3.3 mm. Then it was annealed at 664 °C and the tensile specimens were made from the plate. Fig. 1 shows the shape, dimensions and sample coordinate system (ND means Normal Direction, RD is Rolling Direction and TD is Transverse Direction). Tab. 1 shows the amount of the admixtures in the samples.

Deformation experiments
The samples were deformed on uniaxial tensile machine INSTRON 5882 from strain 5% to strain 30% (strain step was 5%) at room temperature. The structure of the initial (nondeformed by uniaxial tension) sample observed by using light microscope Zeiss Axio Imager ZM1 is in Fig. 2. The grain size is about 20 μm.  The samples were mounted in reflection geometry with its normal parallel to the direction of interest -usually RD, TD, or ND -and the reflected intensities were measured depending on Bragg angle. The resulting peak intensities were normalized to the intensities of a standard sample with random texture by using Mueller formula [4]: where , is measured intensity of hkl reflection for directions = TD, ND and RD, , is intensity of hkl reflection for non-textured sample, is number of reflections measured.
The X-ray texture measurements were performed at theta/theta X'Pert PRO diffractometer with Cr X-ray tube. Full pole figures for planes 101 0 , 0002 , 101 1 and 112 0 were calculated from incomplete pole figures using orientation distribution function (ODF). Observed data were processed by software package X'Pert Texture, PANalytical.

Results
The intensity ratios , calculated (for q=ND, RD and TD) by using Mueller formula from neutronographic data are in Tab. 2. Pole figures measured by X-ray diffraction for planes 101 0 , 0002 , 101 1 and 112 0 for samples deformed at 5%, 15% and 30% are given in Fig. 3.

Discussion
The position of basal poles is tilted from the normal direction toward the transverse direction by 20° for 5% deformation and by 45° for 30% deformation samples (Fig. 3). This rotation indicates twinning. Similar results can be seen from calculated intensity ratios in Tab

Conclusions
From the results reported above it can be seen that samples prefer orientation of planes 101 0 and 112 0 perpendicular to the rolling direction. The results show that, even at low deformations, twinning causes the basal poles orient from the normal direction toward the transverse direction. The split of basal poles toward the transverse direction can be explained by pyramidal slip with a Burgers vector on 112 1 and 101 1 planes [5]. Furthermore, samples prefer orientation of planes 101 2 and 101 3 perpendicular to the normal direction. Texture become stronger with increasing the level of deformation (Tab. 2). The obtained results are characteristic for zirconium [5,6].