Double-layer-coated stainless steel plates resistant to pitting damage

A serious problem encountered when a liquid-Hg target is used for MW-class pulsed spallation neutron source is pitting damage caused to vessel walls. This pitting damage is due to the impact of cavitation-bubble collapse immediately after intense proton beams are made incident on the target. Pitting damage is thought to be as important as or more important than radiation damage in determining the life time of the target. In the present study, an effectiveness of an SS/Au-double-layer-coated SS plate in reducing pitting damage is investigated. An FEM-analysis reveals that the Au layer absorbs the impact from the surface plate and significantly reduced the stress on the SS substrate. SS/Au/SS specimens are fabricated by using the diffusion bonding method, and the development of pitting damage is investigated by using the MIMTM; the specimens were subjected to 560 W impacts, which produced nearly the same morphology of pitting damage in the MIMTM as that observed in proton-beam tests conducted using MW-class proton beams, for 104-106 cycles. The specimens are then analyzed by EDX for determining the thickness of the diffusion layer and by laser microscopy for detecting micro-cracks and the extent of pitting damage.