Surface Integrity of NiTi Alloy by Femtosecond Laser Shock Peening

Aerospace engines made of the NiTi alloy exhibit fatigue damage after a period of service, significantly impacting the reliability of aircraft engines. To address this issue, femtosecond laser surface strengthening treatment is applied to the NiTi alloy. The surface structure and mechanical properties of the laser‐treated NiTi alloy are observed using the white light interference, the Vickers microhardness tester, the X‐ray diffractometer, and the metallographic optical microscope. The results indicate that with the increase of the laser fluence, the surface roughness and microhardness initially increases and then decreases, and the regular ripple structure on the surface gradually disappears. The residual stress increases with the increase of the laser fluence, and it gradually decreases along the depth direction inside the material. The samples after laser shock processing, the X‐ray diffraction peaks exhibit varying degrees of broadening, attributed to the grain refinement and the increased microstress. Under the low‐energy laser‐induced shock waves and interaction with the NiTi alloy surface, plastic deformation and grain refinement occur in the surface layer of the specimen. Under the high‐energy laser irradiation, the laser shock wave becomes more intense, the grain grow abnormally after refinement and deformation.