Research Progress of Laser Shock Peening Technology in Nuclear Power Equipment

Nuclear power is an effective method of generating electricity to address energy shortages and environmental degradation. However, nuclear power safety has been a lifeline for the development of nuclear energy. Materials in nuclear power fields remain in extreme environments and operate under complex stress states. Surface-strengthening technology is currently an important means of enhancing the life of nuclear power equipment materials. Among them, surface deformation strengthening technology is consideredone of the most ideal strengthening methods owing to its advantages of not introducing new materials and the high bonding strength of the membrane base. The most widely used surface deformation strengthening technologies with high maturity include shot peening, rolling, and laser shock peening. Laser shock peening has the advantages of a precise and controllable process, a small effect on the metal surface roughness, no pollution, and a deeper impact layer. To reduce the limitations of its applications, laser shock peening has been developed without coating and femtosecond laser shock peening by simplifying the process. In comparison, the impact layer obtained by conventional laser shock peening was deeper, but the surface roughness was the highest. Laser shock peening withoutcoating has a relatively small effect on the surface roughness of the metal but produces thermal effects, forming holes and cracks. Femtosecond laser shock peening has the smallest effect on the surface roughness but has the shallowest impact layer. Warm laser shock peening, cryogenic laser shock, and electric pulse-assisted laser shock peening have been developed to improve this strengthening effect. Through this review, it was deduced that auxiliary means to enhance the strengthening effect are mainly used in traditional laser shock peening. There has been no targeted research on improving the effect of laser shock peening without coating or femtosecond laser shock peening. The mechanism of laser shock peening is mainly related to the stacking fault energy of the material. The low stacking fault energy metal grain refinement mechanism is dominated by deformation twinning. The high stacking fault energy metal grain refinement mechanism was dominated by the dislocation slip. Currently, the application of nuclear power fields is primarily for basic research on nuclear power materials. Two different strengthening mechanisms are used to improve the mechanical properties of materials commonly used in nuclear power generation. One is the enhancement of the material hardness caused by grain refinement. The other is not grain refinement but a large number of dislocations owing to the material hardness enhancement. The improvement in the wear and corrosion resistance of materials commonly used in nuclear power generation is mainly due to grain refinement and the generation of large residual compressive stresses on the material surface. Through this review, it was deduced that the current research mainly focuses on the in-depth theoretical study of materials and less on the application of practical components. The effects of different processes of laser shock peening on the material performance improvement mechanism are not clear enough, and still need to be coupled with experiments and simulations to verify and reveal the strengthening mechanism. This paper mainly reviews research progress in the field of nuclear power and provides an outlook on the future development direction of laser shock peening in the field of nuclear power to provide a solid theoretical foundation for the laser shock peening with the aim of improving the application of laser shock peening in the field of nuclear power.