Pitting damage morphology of surface modified material. Damage suppression by surface hardening treatment

A Mercury target for spallation neutron source will be installed in MLF (Material and Life-science Facility) in J-PARC (Japan Proton Acceleration Research Complex). The mercury target will be suffered from pitting damage by cavitation erosion. The cavitation will be caused through the pressure wave propagation that induced by thermal expansion of the mercury due to proton beam injection. Surface modification to the vessel wall contact with mercury, such as coatings, surface hardening etc., could exhibit prospective potential to suppress the pitting damage. Hence, cavitation erosion tests on surface modified materials in mercury were performed using electro-Magnetic IMpact Testing Machine (MIMTM) to evaluate the resistance against pitting damage. As a result, it was confirmed that crack and separation occurred on coating layer, because of shear stress due to the mechanical properties change in the interface between the coating and substrate layer. (author)