Damage of multilayered surface by micro-jet impact of liquid metal

Abstract
MW-class spallation neutron sources are being developed in the world. High intensive and energy protons are injected into heavy liquid metals; mercury, lead or lead bismuth, to induce the spallation reaction that produces neutrons. At the moment the proton beams are injected, thermal shock is occurred in the liquid metal and cases pressure waves that excite rapidly the solid container wall. As a result, cavitation bubbles are formed along the interface between the liquid metal and the solid wall. The micro-jet collides against the solid wall at the bubble collapse and damages on the surface. The stainless steel with the multi-layered surface consisting of stainless steel and gold films with 100 μm in thickness was newly developed to mitigate the damage by liquid-metal micro-jet impact. The damage and dynamic response were compared between homogeneous and multi-layered surfaces experimentally and numerically. The stress waves propagation was evaluated along the interface between layers. The dynamic deformation of multi-layered surface is dependent on the thickness of layers and the stress propagation might be dispersed by the interface of multi-layered surface. It can be said that the multi-layered surface improvement is effective to reduce the localized impact deformation.