Comparative Study of the Deformation Behaviour of Zr-2.5 wt% Nb and Excel Pressure Tube Alloys

Author： Salinas-Rodriguez A. Akben M. G. Jonas J. J. Ibrahim E. F.

ISSN： 0008-4433

Source： Canadian Metallurgical Quarterly, Vol.24, Iss.3, 1985-07, pp. : 259-272

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Abstract

Cylindrical specimens machined from Zr-2.5 wt % Nb and Excel alloy pressure tubes were tested at constant true strain rates of 10⁻⁴ and 10⁻¹s⁻¹ in compression over the temperature range 295–1200 K. The specimens were machined to have their axes parallel to the principal directions of anisotropy of the tube, namely, the circumferential, radial and axial directions. The flow curves for both materials were found to depend on the direction of testing as well as on the temperature and strain rate. The direction dependence of the flow stress is interpreted in terms of the crystallographic texture of the pressure tubes. In both materials, the circumferential samples display the highest and the axial ones the lowest flow stresses. This behaviour is consistent with the experimental distribution of basal plane normals which lie principally along the circumferential direction. The flow behaviour of the specimens with axes parallel to the radial and circumferential directions is similar, displaying a high and approximately constant work hardening rate until fracture occurs at low temperatures or flow softening is observed at higher temperatures. However, in the specimens with axes parallel to the axial direction, after an initially decreasing work hardening rate, a regime of almost zero work hardening is observed up to strains of about 0.08. After that, there is a point of inflection and the work hardening rate increases until fracture. This behaviour is attributed to the rotation of the basal poles towards the orientation for 〈c + a〉 slip, and therefore, to a progressively increasing hardening rate.