Effects of Heavy-Ion Irradiation on Microstructure of V-4Cr-4Ti Alloy at Moderate Temperatures

Abstract

AbstractV-4 wt.% Cr-4 wt.% Ti alloy is a promising candidate material for first-wall and structural applications in magnetic fusion reactors. In the past, fast neutron sources were used to evaluate postirradiation properties of fusion candidate materials. The recent shutdowns of the Fast Flux Test Facility (FFTF) and the Experimental Breeder Reactor (EBR-II) left U.S. researchers without local experimental facilities for such tests. Under such circumstances, ease of experimental control, availability, and relatively low cost make heavy-ion irradiation an attractive alternative, provided its limitations are appreciated. We selected 3-MeV V+ and 4.5-MeV Ni++ ions to investigate the effects of irradiation on the microstructure of V-4Cr-4Ti alloy in the temperature range of 200 – 420°C. The main interest is in the evaluation of this alloy's dimensional stability and susceptibility to irradiation embrittlement. In this paper, we report results of ion irradiation experiments and compare them with available data on fast-neutron irradiation. From transmission electron microscopy (TEM) analysis of ion-irradiated specimens, we found that the dominant feature of the postirradiation microstructure was a high density of dislocation loops and pointdefect clusters. Density and defect size depended on irradiation dose and temperature. Precipitates and voids/bubbles were not observed, even in specimens that were simultaneously injected with He and exposed to heavy-ion irradiation. Increased transport of point defects to internal interfaces was observed, as manifested by defect denuded zones along grain boundaries, Defect denuded zones along grain boundaries could lead to segregation of impurities and solutes and formation of precipitates on grain boundaries.