Laser shock processing (LSP) is a novel surface engineering technique that utilizes a nanosecond pulse laser to generate plasma-driven shock waves, which can induce high compressive residual stresses extending to a depth of more than 1 mm from the surface. It has been widely applied to metallic components in aircrafts to improve the fatigue resistance. However, the fundamental mechanisms underlying the effects of LSP on the different materials and their performance remain poorly understood. This manuscript reviews the novel research studies by our team to use experimental approaches to understand the microstructural evolution in metal and ceramic materials during the LSP process, and elucidate the mechanisms that enable LSP to improve mechanical and irradiation properties. In austenitic steels, we discovered that the LSP-induced microstructures could improve the resistance to irradiation damage. The mechanisms are related to the defect sinks generated by LSP such as dislocations and twin boundaries. Compared to metals, LSP has not been widely applied to ceramics and its mechanisms on ceramics are less understood. LSP of alumina ceramics can induce localized plastic deformation near the surface and along grain boundaries. As a result, the mechanical properties of ceramic materials such as fracture toughness can be improved.
Laser shock peening using low-energy nanosecond (ns) fiber lasers was investigated in this study to realize high-speed micro-scale laser shock peening on selected positions without causing surface damage. Due to the employment of a fiber laser with high-frequency and prominent environmental adaptability, the laser peening system is able to work with a much higher speed compared to traditional peening systems using Nd:YAG lasers and is promising for in-situ applications in harsh environments. Detailed surface morphology investigations both on sacrificial coatings and Al alloy surfaces after the fiber laser peening revealed the effects of focal position, pulse duration, peak power density, and impact times. Micro-dent arrays were also obtained with different spot-to-spot distances. Obvious micro-hardness improvement was observed inside the laser-peening-induced microdents after the fiber laser shock peening.