Corrosion Resistance of Amorphous Fe_49.7Cr_17.7Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4 Coating: A New Criticality Control Material

An iron-based amorphous metal with good corrosion resistance and a high absorption cross section for thermal neutrons has been developed and is reported here. This amorphous alloy has the approximate formula Fe_49.7Cr_17.7Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4 and is known as SAM2X5. Chromium, molybdenum, and tungsten were added to provide corrosion resistance, while boron was added to promote glass formation and the absorption of thermal neutrons. Since this amorphous metal has a higher boron content than conventional borated stainless steels, it provides the nuclear engineer with design advantages for criticality control structures with enhanced safety. While melt-spun ribbons with limited practical applications were initially produced, large quantities (several tons) of gas-atomized powder have now been produced on an industrial scale, and applied as thermal-spray coatings on prototypical half-scale spent-nuclear-fuel containers and neutron-absorbing baskets. These prototypes and other SAM2X5 samples have undergone a variety of corrosion testing, including both salt-fog and long-term immersion testing. Modes and rates of corrosion have been determined in various relevant environments and are reported here. While these coatings have less corrosion resistance than melt-spun ribbons and optimized coatings produced in the laboratory, substantial corrosion resistance has been achieved.