Hydrogen Kinetics and Hydride Formation Effect on Zr-1Nb and Zr-1Nb-1Sn-0.1Fe Alloys for Nuclear Application

Abstract

The purpose of this study was to investigate the kinetics of hydrogen absorption and hydride formation and their effect on the mechanical properties in Zr-1Nb and Zr-1Nb-1Sn-0.1Fe alloys, which were thermomechanically processed and gaseously hydrided at 320ºC under 10 bar hydrogen pressure. X-ray diffraction (XRD) confirmed the formation of α-Zr matrix after final heat treatment. The alloys absorbed almost the same amount of hydrogen, although with different kinetics. Absorption began almost immediately in Zr-1Nb alloy whilst in Zr-1Nb-1Sn-0.1Fe hydrogen absorption started after 11 h besides a faster hydrogen kinetics. Results showed that tensile strengths for both alloys were nearly independent of absorbed hydrogen. Fractographic examinations indicated ductile fractures for unhydrided condition whereas quasi-cleavage features were observed for all hydrided specimens.

Hydrogen Effect on Zr-Nb-Mn Alloys for Nuclear Reactor Application

“…Zr-0.9Nb-0.1Mn required one more pass, compared with the other compositions, to reach the same total reduction planned for hot and cold rolled steps. This results are in accordance with Ribeiro et al 6 , which processed a Zr-0.8Nb-0.2Mn alloy by cold rolling and obtained a plate with no significant cracks and also can be comparable to Oliveira et al 11 that obtained the same surface results when processing Zr-1Nb and Zr-1Nb-1Sn-0.1Fe alloy through a similar deformation process. Figure 3 shows the diffraction pattern of Zr-0.9Nb-0.1Mn, Zr-0.8Nb-0.2Mn and Zr-0.6Nb-0.4Mn under different processing conditions.…”

“…Non-hydrides specimens presented secondary cracks, which may explain the low values of yield strength and resistance observed for alloys with higher niobium content. The presence of secondary cracks in commercial zirconium alloys under similar processing conditions was observed by Oliveira et al 11 . Zr-0.9Nb-0.1Mn presented long cracks, around 250 µm, perpendicular to the loading direction, while the compositions with higher manganese content had smaller, 10-20 µm, and less oriented cracks, Figure 8 For the hydrogenated alloys, ductile fracture features were prevalently accompanied by the presence of secondary cracks with a quasi-cleavage aspect, typical of hydride embrittlement.…”

“…The time and temperature of the heat treatment were defined based on Tian et al 2 , which indicated that a fully recrystallized microstructure could be achieved at 873 K after 84 minutes in a 30% deformed Zr-1Nb alloy. Additionally, Oliveira et al 11 obtained a partially recrystallized microstructure with fine precipitation by 2 h at 873 K annealing through a thermomechanical process similar to this work.…”

“…The XRD analyses indicate that all alloys have an α-Zr matrix. The β-phase precipitates could not be observed by XRD due to their low volume fraction 6,11 . TEM micrographs for the Zr-0.6Nb-0.4Mn alloy after heat treatment at 923 K for 2 h, Figure 4, show the presence of spherical and well-dispersed precipitates, with a mean radius of 1.8 nm in the zirconium matrix, confirming TC-Prisma simulation results, presented in Table 1.…”