Characterization of hydrides precipitated in the á-Zr matrix of zirconium alloys: effects of stress, microstructure and neutron irradiation on hydride dislocation structure, texture, and terminal solid solubility.

P. VIZCAINO; A.V. FLORES; VICENTE ALVAREZ, M.A.; SANTISTEBAN, J.R.; A. TOLLEY; A.CONDO; ALMER, JONATHAN

Manchester

Simposio; 19th International Symposium of Zirconium on the nuclear Industry; 2019

ASTM

Synchrotron X-ray diffraction, TEM and HRTEM experiments were performed onsamples from Zr-2.5Nb pressure tubes and Zircaloy-4 tubing in order to define hydrideprecipitation temperatures, hydride texture, matrix hydride orientation relationship anddislocation densities. For Zr-2.5Nb, studies included in-situ constant stress testsperformed on dog bone specimens cycled between room temperature and 400°C, wherehydrides were completely dissolved and re-precipiated. For Zircaloy-4, analysisincluded ex-service Zircaloy-4 irradiated to~1022neutrons/cm2. Careful interpretationand analysis of azimuthal variations around the Debye-Scherrer rings allowed a cleardescription of both texture and dislocation densities of ä-hydride precipitates. The mainfindings are:- In Zr-2.5Nb pressure tubes the terminal solid solubility for hydride dissolution (TSSD)and precipitation (TSSP) temperatures depend on the orientation of the parent á-ZrPage 2 of 38https://mc04.manuscriptcentral.com/astm-stpSTP: Selected Technical Papers123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Review Only2grain. Hydrides both precipitate and dissolve at slightly lower temperatures (~5°C and~15°C, respectively), in grains having their c-axis parallel to the tube hoop direction,than those with their c-axis ~20° off from the hoop direction.- Application of a stress along the tube hoop direction during precipitation increasesTSSP temperatures and favors hydride precipitation on grains with c-axes stretched bythe load. For grains with c-axis parallel to the applied load, TSSP temperaturesincreases at a rate of (0.08 ± 0.02)°C/MPa, nearly two orders of magnitude higher thanprevious estimates.- Precipitates of ä-hydride are heavily dislocated, yet displaying large variations (1.6-10x 1014 m-2) depending on the microstructure and H content of the parent material.