Investigating the thermal stability of irradiation-induced damage in a zirconium alloy with novel in situ techniques

Abstract

Zr alloys exhibit irradiation-induced growth and hardening which is associated with the defects and dislocation loops that form during irradiation. In this study, state-of-the-art in-situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM) techniques were used to investigate the stability of dislocation loops in two proton-irradiated Zr-Fe binary alloys in real time. Complementary data from both techniques show rapid annealing of a-loops occurs between 300°C and 450°C. Line profile analysis was performed on the SXRD patterns using the convoluted multiple whole profile analysis tool, to calculate the change in a-loop line density as a function of post-irradiation heat treatment temperature and time. At temperatures below 300°C, no significant decrease in a-loop density was detected when held for one hour at temperature. From this SXRD experiment, we calculate the effective activation energy for the annealing process as 0.46 eV. On-axis in-situ STEM imaging was used to directly observe a-loop mobility during heating cycles and confirm that a-loops begin to glide in the trace of the basal plane at ~200°C in a thin foil specimen. Such a-loop gliding events, leading to annihilation at the foil's surfaces, became more frequent between 300-450°C.

Microscopic structure of a heavily irradiated material

“…How do the above simulations compare with experimental observations? At the beginning of this study, we noted that the intrinsic relaxation timescales of evolution of microstructure may be macroscopic even if the temperature is relatively high, and can vary from hours [40,41] to weeks [42] and even months [38]. If the dose-rate is sufficiently high such that the corresponding irradiation timescale is shorter than the relaxation time of the evolving microstructure, athermal stress driven processes will dominate the evolution.…”

“…The recovery of dislocation loops in aluminium at room temperature occurs on the timescale of 230 years [39]. No significant dynamics is observed in tungsten irradiated to 1.6 DPA on the timescale of an hour [40] at temperatures up to 800 • C. Irradiated zirconium [41] does not visibly evolve at temperatures below 300 • C. The microstructure of irradiated steels remains stationary on the timescale of a week [42] at T 330 • C. Treating defect and dislocation microstructure as a dynamic entity evolving by thermal activation is only necessary in the limit t τ . If the rateφ of generation of defects by irradiation is higher than τ −1 , then microstructural evolution is driven by factors other than thermal activation.…”

The effect of irradiation temperature on damage structures in proton-irradiated zirconium alloys

“…previously to study dislocation densities in neutron-and proton-irradiated zirconium alloys [18,[41][42][43] using the Krivoglaz-Wilkens model [44][45][46], for the strain contribution to peak profiles, ℎ :…”

Characterizing dislocation loops in irradiated polycrystalline Zr alloys by X-ray line profile analysis of powder diffraction patterns with satellites

“…Although X-ray LPA has proved to be an excellent and effective complementary tool to TEM in determining dislocation densities and arrangements, crystallite sizes, and planar defect densities in crystalline materials with very different structures (Warren, 1959;Wilkens, 1970;Borbé ly & Groma, 2001;Scardi & Leoni, 2002;, some genuine problems and apparent discrepancies arise in data for irradiated materials such as irradiated zirconium alloys (Griffiths et al, 1992(Griffiths et al, , 2002Griffiths, 2008;Balogh et al, 2012Balogh et al, , 2016Balogh et al, , 2018Harte et al, 2015;Seymour et al, 2017;Topping et al, 2018Topping et al, , 2019):…”