Incorporation of gadolinium and boron into Zirconium alloy: Surface alloying of immiscible materials using an intense pulsed ion beam

摘要

We investigate the potential for incorporation by surface alloying of two elements, gadolinium (Gd) and boron (B), into Zr-alloy substrates, by the application of an intense ion beam pulse to a conventionally pre-applied Gd or B thin film coating to the substrate. The beam is produced by the Repetitive High Energy Pulsed Power-1 (RHEPP-1) ion beam facility at Sandia National Laboratories. Surface alloying is desirable in this case for two reasons: (1) conventional alloying is not possible because both Gd and B have negligible solubility in Zr at room temperature, and (2) a conventionally applied coating without surface alloying may be expected to delaminate in the harsh end-environment where the elements are used (e.g. fission reactors). While surface alloying has been a topic of investigation both by the present and prior researchers, the goal of the present work is the detailed study incorporating heat flow simulations and a full complement of materials analysis tools to characterize surface alloying of Zr-alloy substrates with Gd and B. Use of code simulations is essential for predicting appropriate film thickness and ion beam treatment fluences, which are specific to a given film-substrate system. Characterization after ion beam surface treatments confirmed successful alloying of both Gd and B by significant extension of their solid solubility in Zr-alloy substrates. While Gd surface alloying of Zr-alloys resulted in unacceptable oxidation in thermal and environmental conditions mimicking a nuclear reactor environment, B surface alloying resulted in acceptable corrosion resistance comparable to the as-received Zr-alloys.