[en] 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 295-1200K. 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

No abstract available

[en] Very regular twin structures can be formed in textured industrial Zr-2.5% Nb alloy by compression along a direction which does not - or only to a very limited extent - lie in basal planes of the crystallites. Single or co-operative twins arise in rolled rods or tubes through plastic deformation if this exceeds 2%. Those twins have the appearance of regular strips at an angle about 45⁰ to the rolling direction. Their length is determined by grain size or by dimensions of areas with stable crystallographic grain orientation. For sharper tube texture, the twin length exceeds that for rods. The thickness of the twins increases with the degree of deformation. The maximum twin thickness is limited by grain size, which is 4-7 μm for the material investigated. With increase in deformation, the form of the twins changes from strips to a lenticular shape and with further increase eventually to the shape of normal grains. This is the phenomenon of the transformation of twins into grains. The twin structure is stable and preserved after standard annealing. The above considerations for Zr-2.5% Nb may indeed be applicable to other α-Zr alloys. (orig.)

No abstract available

[en] Zr-2.5 wt% Nb pressure tubes in CANDU reactors are cold-drawn to achieve the desired mechanical strength and tube dimensions. As part of an assessment of possible alternative fabrication processes, a pressure tube was cold-worked by pilgering and its dimensional stability monitored during service in the U-1 loop in the NRU test reactor. Strain rates have been determined for the pilgered tube from measured diameter and length changes after 22,060 h of reactor operation. These rates were compared with those for a cold-drawn tube also tested in NRU, and with the calculated behaviour of current power reactor pressure tubes extrapolated to the NRU test conditions. The deformation rates of the pilgered tube were found to be only marginally inferior to those of cold-drawn tubes

[en] Delayed hydride cracking in zirconium alloys is caused by the repeated precipitation and cracking of brittle hydrides. The growth kinetic of the hydrides have been measured to evaluate the critical hydride length for crack initiation. Hydride growth leading to crack initiation follows an approximate (time)^1/3 law on the average; crack propagation proceeds in a stepwise fashion. The critical length of hydride for crack initiation increases with stress and temperature. The fracture criterion for crack initiation predicts the critical hydride length at a give stress level and temperature. The fracture initiation mechanism of the hydride confirms the temperature effects for heating and cooling cycles under services loads. (orig.)

[en] The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy

No abstract available

[en] Previously obtained ⁹⁵Nb interphase diffusion coefficients were re-evaluated taking into account more recent β-phase lattice diffusivity values obtained by other authors. The new Arrhenius plot is a straight line if the lowest temperature point is neglected and the diffusion parameters, according to the Fisher-Bondy model, are Q_i = (288±30) kJ/mol and D_0i = (0.89±0.4)x10⁴ m²/s, with δ = 5x10^-10 m. The enhanced interphase diffusivity value for low temperatures with respect to the straight line is ascribed to the lack of structural stability of the samples during the diffusion anneal. This would affect more the Nb diffusion, because Nb is the minor component of the alloy, than the Zr diffusion. (orig.)

[en] The Zr-2.5 wt percent Nb pressure tubes used in CANDU reactors are manufactured via hot extrusion, followed by cold-working. This manufacturing process causes the crystallographic structure of the alloy to be strongly textured and the grains to be elongated in the axial direction. The mechanical properties are consequently anisotropic. Uniaxial tensile and creep tests carried out between 20 and 700 degrees C on specimens oriented in both the axial and transverse directions showed that the anisotropic behaviour varied with temperature. The effects of texture, grain shape and two-phase structure on these changes in anisotropic behaviour are discussed