History of Laser Peening Without Coating (LPwC): From Invention to Future Developments

Laser peening without coating (LPwC) was invented in Japan in the 1990s. After confirming the effect of reducing the stress corrosion cracking (SCC) susceptibility of sensitized materials, LPwC has been applied to operating nuclear power reactors as a countermeasure against SCC of in-core components. Meanwhile, fiber-delivery technology for high-power laser pulses has been developed to expand the applicability of LPwC. In parallel, the effect of LPwC to improve fatigue properties has been investigated and then applied to the inside of the connecting pinholes at the root of nuclear steam turbine blades. In the last decade, various technological developments have been made to further expand the applications, such as dry LPwC, which does not use water as a confinement medium, and handheld LPwC, which uses a finger-sized microchip laser mounted directly on a robot. The author reviews the activities in LPwC over the past 30 years, focusing on the underlying physics, inventions, applications, and future developments.