Layer dissolution in accumulative roll bonded bulk Zr/Nb multilayers under heavy-ion irradiation

The heavy-ion irradiation behavior of bulk zirconium-niobium multilayered composites was investigated up to large doses. Multilayers with an average individual layer thicknesses ranging between 15 and 80 nm were synthesized by accumulative roll bonding technique. The irradiation was performed with a defocused 7 MeV Zr2+ ion beam at 500 degrees C. The maximum dose achieved was similar to 145 dpa at the depth of similar to 1.5 mu m from the irradiated surface. Sub-surface microstructural damage and the chemical redistribution were characterized by transmission electron microscopy and energy dispersive spectroscopy, respectively. Irrespective of the layer thicknesses, the irradiation condition caused layer instability and the extent of damage varied with the dose levels. Doses lesser than similar to 60 dpa caused layer fragmentation and greater than similar to 60 dpa resulted in layer dissolution. The chemical mixing of layers occur to a depth of -1 mu m, consuming multiple bi-layer periods. Despite the elevated irradiation temperature (500 degrees C) and a slightly positive heat of mixing (+6 kJ/mol), no phase separation was observed and single-phase was retained in the mixed region. The results demonstrate that chemical mixing was facilitated by the liquid phase miscibility of Zr and Nb, which propelled the interdiffusion within the thermal spikes towards mixing. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The heavy-ion irradiation behavior of bulk zirconium-niobium multilayered composites was investigated up to large doses, revealing layer instability and damage variation with dose levels. Despite the elevated irradiation temperature and slight positive heat of mixing, no phase separation was observed, demonstrating the chemical mixing facilitated by liquid phase miscibility of Zr and Nb.