Study on the mechanical properties and microstructure of Zr-2.5wt%Nb pressure tube material

Abstract

In order to study the mechanical properties and the anisotropy of a Zr-2.5 wt%Nb pressure tube material, tensile tests along the principal tube directions, which are axial, transverse and radial, were performed at room temperature using a pressure tube. The effect of tube length was evaluated, by using samples from the tube's back-end, middle, and front-end. Strong anisotropy among the principal directions was found, and increased strengths were obtained with increased distance from the front-end location. Microstructure analysis by X-ray diffraction, electron backscatter diffraction, and scanning electron microscopy indicated that increasing defect density along the tube was the main reason for the increasing strength. Although texture mainly determined the anisotropy of the tensile strengths, the ratio between the axial and radial strengths could be considerably altered by hydride plates. Depending on how the hydride plate was placed with regard to the deformation direction, the yield strength and strain hardening ability were reduced differently by the hydride. The deterioration effect of the hydrides did not show linear dependency on the hydrogen contents due to other microstructure variations. We had a brief discussion about which parameters might result in the non-linear change found in the deterioration along the tube.