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Abstract
To combat liquid metal corrosion from lead–bismuth eutectic coolant in the fuel cladding and coolant piping of generation IV fast fission reactors, a composite that employs a Fe–Cr–Si steel layer weld clad on a structural layer of alloy T91 (Fe–9Cr–1Mo) is being developed. Diffusion of Si away from the cladding during service can compromise corrosion resistance, whereas carbon redistribution will affect mechanical properties and phase stability. Diffusion of silicon and carbon in a manufactured sample of the composite has been investigated both experimentally and by modelling. The diffusion coefficient for silicon in the T91/Fe–12Cr–2Si system was found to be 1·36 × 10−12 cm2 s−1 at 650°C, implying that concentration in the clad layer should not drop below 1·25%Si at a distance of 51 μm from the interface after 50 years' service at 650°C. The rapid carbon diffusion observed should be helpful during processing and operation. The two layers will have similar properties once carbon diffuses into the cladding, reducing the probability of mechanical property mismatch based errors during processing. The increased hardness of the carbon enriched clad layer will result in higher strength during operation, reducing the likelihood of damage or abrasion.