Effect of Cold Work on Hydrogen Diffusion in Zr-2.5Nb Alloys at Reactor Temperatures

摘要

To investigate hydrogen diffusion in Zr-2.5%Nb,specimens in the form of rods were used in the followingconditions – (ⅰ) annealed (as the control specimen) and(ⅱ) cold worked (at different levels). A hydride layerdeposited at one end of the specimen or hydrideshomogenously distributed within one half of the specimenacted as the hydrogen source. Diffusion anneals at 270°C and 300 °C were performed. The diffusion coefficientswere determined by fitting Fick’s law to the measured thehydrogen concentration profiles determined using hotvacuum extraction mass spectrometry (HVEMS) assumingone-dimensional diffusion along the axial direction.The diffusion coefficients measured from theannealed specimens are consistent with literature. Somemeasurements on the annealed specimens were performedwith residual hydride layers. Preliminary analysissuggests that the differences in the observed diffusioncoefficients for specimens with and without residualhydride layers could be explained by the stress gradientscaused by the residual hydrides and the concentrationgradient predicted by Fick’s Law.The diffusion coefficients measured on the coldworked specimens increased significantly (～60%), andalmost linearly, with increasing cold work (0 to 14%) at270 °C; whereas, the increase was less prominent(< 20%) at 300 °C. Heterogeneous diffusion in thevicinity of dislocation structures is postulated as the causefor the increased diffusion with cold work; while possiblerecovery at 300 °C is hypothesized to be diminishing thiseffect of cold work or the role of heterogeneous diffusionis decreased at elevated temperatures.