In-situ annealing of self-ion irradiation damage in tungsten

PDF / 46,533,018 Bytes
6 Pages / 612 x 792 pts (letter) Page_size
37 Downloads / 225 Views

In-situ annealing of self-ion irradiation damage in tungsten Xiaoou. Yi1, Michael L. Jenkins2, Steve G. Roberts1 and Marquis A. Kirk3 1 Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, U.K. 2 Trinity College, University of Oxford, Broad Street, Oxford, OX1 3BH, U.K. 3 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A. ABSTRACT In our earlier work [1] microstructural evolution in tungsten under self-ion irradiation was investigated as a function of temperature and dose by in-situ 150 keV W+ ion irradiations on the IVEM-Tandem facility at Argonne National Laboratory (ANL). The present work focuses on the thermal stability of this damage. Thin foils of tungsten were irradiated at room temperature (R.T.) to fluences up to 1018 W+m-2 (~ 1.0 dpa) and were then annealed in-situ for up to 120 min at temperatures between 300 and 800°C. We found that: (1) loops with Burgers vectors ½ and coexist during annealing; (2) is not a stable loop configuration above 300°C and the fraction of such loops decreased with increasing temperature and/or time; (3) changes in loop populations during annealing were very sensitive to temperature, but less sensitive to time. The majority of changes occurred within 15 min, and were associated with the loss of small (1-2 nm) dislocation loops. The origin of these trends is discussed by considering defect mobility and the energetics of defect configurations predicted by previous DFT calculations [2]. INTRODUCTION Tungsten is a prime candidate for building divertor components in fusion reactors. During service, this component would be subject to fast neutron displacement damage at temperatures between ~ 500°C -1200°C, depending on location. Six annealing stages of radiation-induced damage in neutron irradiated tungsten have been identified based on the recovery of electrical conductivity during heat treatments [3-6]. Each corresponds to the migration of one or a few defect species. The stages relevant to fusion power applications are: stage III (130 - 450°C), stage IV (450 - 650°C), stage V (650 - 1000°C) and stage VI (1000 1500°C). Stages III, IV and V have been closely investigated and are in accordance with the migration of monovacancies (III), bivacancies and impurity complexes (IV), and vacancy clusters (V) respectively. Self interstitials become mobile as low as -170°C, corresponding to stage I [7]. It is the purpose of this paper to correlate the annealing stages of tungsten with quantitative investigations of the annealed damage microstructures and provide plausible explanations for the evolving trends observed. EXPERIMENT AND RESULTS Pure tungsten (> 99.996 wt %, ~ 100 μm sheet, Plansee Group) was heat treated in vacuum at 1400°C for 20 hours to remove dislocations introduced by processing. Discs of diameter 3 mm were punched and then electropolished to electron transparency using a twin-jet apparatus. A total of five R.T. irradiations with 150 keV W+ ions were performed on the IVEMTandem at ANL to a fluence of 1018 W+m-2 (~ 1.0 dpa)