Enhancement of Surface Properties of Metal Materials by Underwater Laser Processing

抄録

The authors have developed underwater laser processing, namely welding and peening, to enhance surface properties of metallic components. The process developed could significantly reduce radiation dose to workers in nuclear facilities due to the shielding effect of water from radiation as well as due to remote operation attainable by laser technologies. Laser welding or cladding makes corrosion-resistant layers on the surface of components underwater, which reduces stress corrosion cracking (SCC) susceptibility. Various metallurgical and mechanical tests were performed to prove that the laser cladding made sound layers even if the surface had been degraded. Laser peening imparts compressive residual stress in near-surface layers by irradiating intense laser pulses without any surface preparation. High pressure plasma generated through ablative interaction underwater impinges on the surface and induces plastic strain to make compressive residual stress. Both processes are used to enhance surface properties, such as resistance to SCC, fatigue or wear of various metal materials.